Psoriasis

Clinical Snapshot

Psoriasis is a chronic, immune-mediated skin disease driven by dysregulated interleukin-23/interleukin-17 (IL-23/IL-17) axis signalling, producing markedly increased epidermal cell turnover.^[1] Plaque psoriasis (also called psoriasis vulgaris) is the most common subtype and the focus of this chapter, presenting as inflamed, thickened, well-demarcated plaques with overlying silvery scale, classically on the scalp, extensor elbows and knees, sacral area, and nails. Erythrodermic, guttate, and generalized pustular psoriasis are distinct, less common subtypes with their own presentations and, for the latter two, dermatologic-emergency potential (see Red Flags & Refer) — they are not covered in depth here. Psoriasis is a systemic disease, not just a skin disease: up to one-third of patients develop psoriatic arthritis, and cardiovascular disease, metabolic syndrome, dyslipidemia, diabetes, hypertension, inflammatory bowel disease, and depression/anxiety all occur more often alongside it, which is why comorbidity screening is a standing part of every visit, not an afterthought.^[1] Correct diagnosis matters before any treatment decision is made — several common conditions mimic psoriasis at each affected site, and the wrong diagnosis leads to the wrong treatment (see the differential tables in Assessment & Diagnosis).

Recognize the Condition

Core lesion morphology

Classic plaque psoriasis presents as well-demarcated, inflamed plaques with overlying silvery-white scale. Plaques appear pink-to-red in lightly pigmented skin and purple, dark brown, or grey in darkly pigmented skin, where the erythema and scale can both be far less obvious — a real cause of diagnostic delay if the exam is anchored to the classic light-skin description. Postinflammatory pigmentary change can persist for months after plaques have cleared, particularly in darkly pigmented skin, and should not be mistaken for active disease. The Koebner phenomenon — new psoriatic plaques forming at sites of skin trauma (scratches, surgical scars, sunburn, tattoos) — is characteristic and is a practical reason to counsel patients to minimize skin trauma.

Presentation by body region

Scalp

Thick, adherent scale, often extending slightly beyond the hairline onto the forehead, ears, or nape. Seborrheic dermatitis is the main mimic (see below); when the two overlap or cannot be distinguished, the descriptive term "sebopsoriasis" is used and management follows the scalp-psoriasis approach.

Face

Uncommon relative to other sites; when present, it is often an extension of scalp disease onto the upper forehead. Sharply demarcated plaques with silvery scale, in contrast to the mimics below.

Trunk and extremities

The classic distribution: extensor elbows and forearms, extensor knees and shins, lower back, and the gluteal fold. Well-demarcated, inflamed plaques with overlying scale.

Fold (intertriginous) areas

Axillae, groin, inframammary folds, and gluteal cleft. Scale is often minimal or absent at these moist, occluded sites, which is a frequent source of diagnostic confusion — the plaque instead appears as a well-demarcated, bright pink-to-red (lightly pigmented skin) or purple/dark-brown/grey (darkly pigmented skin) patch.

Palms and soles

Well-demarcated scaling and hyperkeratosis, often bilateral and symmetric, on weight-bearing areas of the soles and across the palms. One of the more difficult sites to treat given skin thickness and mechanical stress; minimize trauma to these areas to avoid Koebnerization.

Nails

Pitting of the nail plate, onycholysis (lifting of the nail plate), subungual hyperkeratosis, nail plate crumbling, and splinter hemorrhages. Nail involvement is often more numerous and symmetric than in a fungal nail infection, and psoriasis is usually present at other skin sites too — nail clipping/fungal culture can help distinguish the two when it is unclear, and the two can coexist.

Up to one-third of patients with psoriasis develop psoriatic arthritis, which can affect peripheral joints, the axial spine, entheses (tendon/ligament insertion points), and produce dactylitis ("sausage digit") — new joint symptoms in a patient with psoriasis should always be actively asked about (see Assessment & Diagnosis and Red Flags & Refer).^[2]

Risk Factors

Family history of psoriasis — almost half of patients report an affected relative; genetic predisposition plays a major role.
Smoking — associated with increased psoriasis severity; ask about smoking status in every patient and offer cessation support.
Excessive alcohol consumption — associated with increased severity, and relevant to treatment selection given the hepatotoxicity of methotrexate and acitretin.
Obesity — associated with increased disease severity and with reduced response to some systemic therapies; weight management is a genuine adjunct to disease control, not just general health advice.
Physical trauma to the skin (Koebner phenomenon) — scratches, sunburn, tattoos, and surgical scars can trigger new plaques at the trauma site.
Certain medications can trigger or worsen psoriasis, including lithium, beta-blockers, antimalarials, interferon, and, on withdrawal, systemic corticosteroids — ask about new or changed medications when a patient's psoriasis unexpectedly worsens.
Streptococcal pharyngitis is a recognized trigger specifically for guttate psoriasis (not covered in depth in this chapter).
Psychological stress is commonly reported by patients as a trigger for flares, though the evidence base for this association is less rigorous than for the factors above.

Red Flags & Refer

Most psoriasis is not an emergency, but a small number of presentations and treatment-related complications need urgent escalation.

Erythrodermic psoriasis — diffuse erythema and scaling involving most of the body surface area, with risk of fluid/electrolyte imbalance, impaired thermoregulation, high-output cardiac failure, and sepsis. This is a dermatologic emergency requiring same-day assessment, often hospitalization.
Generalized pustular psoriasis (von Zumbusch pattern) — widespread sterile pustules on erythematous skin, often with fever and systemic illness. Also a dermatologic emergency requiring urgent assessment, often hospitalization.
Abrupt withdrawal of systemic corticosteroids, or of a potent topical corticosteroid used for psoriasis, can itself precipitate a rebound flare or trigger generalized pustular psoriasis — this is a prescribing-related red flag pharmacists are well positioned to catch and prevent by counselling against abrupt discontinuation.
Signs of a significant infection in a patient on an immunosuppressive or biologic agent (methotrexate, cyclosporine, apremilast, deucravacitinib, or any biologic) — fever, spreading redness, or systemic illness warrants prompt medical assessment and, generally, holding the immunosuppressive therapy until the infection is addressed.
New joint pain, swelling, stiffness (especially morning stiffness lasting more than 30 minutes), or a swollen "sausage" digit (dactylitis) in a patient with psoriasis — suggests psoriatic arthritis and warrants prompt evaluation, since delayed treatment is associated with irreversible joint damage.^[2]
Rapid or progressive worsening despite an adequate trial of topical therapy, or psoriasis affecting more than 10% of body surface area, a cosmetically or functionally sensitive site (face, genitals, palms/soles), or causing significant quality-of-life impact — these patients need referral for consideration of phototherapy or systemic therapy rather than escalating topical potency indefinitely.

Assessment & Diagnosis

Face: differentiating psoriasis from its mimics

Parameter	Psoriasis	Seborrheic dermatitis	Discoid lupus erythematosus	Tinea faciei
Scale	Sharply demarcated, silvery scale	Greasy, yellowish scale	Adherent, "carpet-tack" scale with scarring	Little or no scale except at the margin
Distribution	Sharply demarcated plaques, often an extension of scalp disease onto the forehead	Eyebrows and perinasal area typically involved	Photo-exposed areas; scarring is a distinguishing feature	Central clearing with an active, scaly margin
Confirmatory test	Clinical; psoriasis at other sites supports the diagnosis	Clinical	Skin biopsy if diagnosis is uncertain	KOH scraping or fungal culture positive

Hands and feet: differentiating psoriasis from its mimics

Parameter	Plaque psoriasis	Tinea	Eczema
Lesion	Well-demarcated scaling, hyperkeratosis	Scaling may have an annular (ring) shape with central clearing; rarely vesicles	Poorly defined scaling, fissures, vesicles, crusting
Toe-web changes	Maceration between all toes	Interdigital maceration and scaling, particularly between the 4th and 5th toes	Maceration between all toes
Site	Weight-bearing areas of the soles; bilateral, symmetric	Instep area; asymmetric	Weight-bearing area; symmetric
Nail changes	Pitting, yellow discoloration, onycholysis	Asymmetric changes with subungual hyperkeratosis and onycholysis suggestive of a fungal nail infection	Nonspecific nail changes
Other clues	Psoriasis present at other body sites	Tinea cruris often coexists; KOH scraping or fungal culture confirms	Eczema at other sites; personal or family history of atopy (asthma, allergic rhinitis)

Fold (intertriginous) areas: differentiating psoriasis from its mimics

Parameter	Psoriasis	Tinea	Eczema	Candidiasis
Appearance	Well-demarcated, bright pink/red (lightly pigmented skin) or purple/dark-brown/grey (darkly pigmented skin); scale is often minimal or absent at this site	Scaling concentrated at the advancing edge	Very itchy, excoriated, crusty	Bright red (lightly pigmented skin) or minor colour change/hyperpigmentation (darkly pigmented skin), with satellite papules and pustules beyond the main patch
KOH test	Negative	Positive	Negative	Positive
Other clues	Psoriasis present at other body sites	Maceration concentrated between the 4th and 5th toes	Eczema at other sites	Predominates specifically in fold areas; may complicate psoriasis at the same site (see Choose Initial Treatment)

Trunk and extremities: differentiating psoriasis from its mimics

Parameter	Psoriasis	Pityriasis (tinea) versicolor	Pityriasis rosea	Atopic dermatitis	Tinea corporis
Key features	Well-demarcated, inflamed plaques with overlying silvery scale on extensor surfaces	Multiple macules coalescing into patches on the upper torso; colour ranges from reddish-brown to pink to paler than background skin; fine scale apparent when scratched	A single "herald" patch followed by an eruption of oval pink (lightly pigmented skin) or grey/brown/black (darkly pigmented skin) plaques with a fine collarette of central scale, mostly on the trunk	Very itchy, often crusty, lichenified, and excoriated; personal or family history of atopy	Scaly, inflamed lesions with an active peripheral margin and central clearing
Confirmatory test	Clinical; psoriasis at other typical sites supports the diagnosis	KOH scraping shows short hyphae and spores ("spaghetti and meatballs")	Clinical; self-limited course	Clinical; personal/family atopy history	KOH scraping or fungal culture positive

History

Onset, duration, and pattern of skin lesions; personal or family history of psoriasis or psoriatic arthritis.
Joint symptoms — pain, swelling, stiffness (especially morning stiffness over 30 minutes), a swollen digit, or heel pain — at every visit, using a structured screen (see PEST below) rather than only asking generally.
Triggers: recent infection (especially streptococcal pharyngitis for guttate psoriasis), new medications (lithium, beta-blockers, antimalarials, interferon), skin trauma, and psychosocial stress.
Impact on quality of life, sleep, work/school, and mental health — depression and anxiety are more common in psoriasis and should be actively screened for, not assumed absent.
Cardiovascular risk factors and other comorbidities (obesity, diabetes, hypertension, dyslipidemia, inflammatory bowel disease) — screen for these directly, particularly in moderate-to-severe disease, and refer for management as needed.^[1]

Examination and severity assessment

Examine the scalp, nails, and typical extensor/flexural sites even if the patient's chief complaint is a single area, since involvement elsewhere supports the diagnosis and informs severity. Estimate body surface area (BSA) involvement using the patient's own palm (including fingers) as a rough guide to 1% BSA. A widely used practical classification: mild disease is under 3% BSA, moderate disease is 3-10% BSA, and severe disease is over 10% BSA — though involvement of a special site (face, scalp, palms/soles, genitals, nails) or a significant quality-of-life impact can make even a lower-BSA case a candidate for systemic therapy regardless of the percentage (see Choose Initial Treatment).^[3] Formal severity indices (PASI — Psoriasis Area and Severity Index; BSA percentage) are clinician-assessed composite ratings used mainly in dermatology practice and clinical trials to track treatment response over time, rather than a simple point-sum screening score — they are not reproduced here as a self-scoring tool.

Screening for psoriatic arthritis: the Psoriasis Epidemiology Screening Tool (PEST)

Ask every psoriasis patient without an existing psoriatic arthritis diagnosis about joint symptoms at least annually, using a structured tool rather than relying on the patient to volunteer joint complaints — many patients do not connect joint pain with their skin disease. The PEST questionnaire is a simple 5-question, 1-point-each screening tool.^[4]

Question (1 point each if "yes")
Have you ever had a swollen joint (or joints)?
Has a doctor ever told you that you have arthritis?
Do your nails have holes or pits?
Have you had pain in your heel?
Have you had a finger or toe that was completely swollen and painful for no obvious reason?

A total score of 3 or more (out of 5) is a positive screen and warrants referral to rheumatology for further assessment — a positive PEST does not by itself confirm psoriatic arthritis, since it can also flag other inflammatory arthritides or fibromyalgia, but it identifies patients who need specialist evaluation rather than reassurance.^[4]

When testing is not needed

Classic plaque psoriasis at typical sites is a clinical diagnosis — skin biopsy is not routinely needed and should be reserved for atypical presentations or when a mimic (see the tables above) cannot be excluded clinically. A KOH scraping or fungal culture is worthwhile whenever tinea is a realistic possibility (fold areas, palms/soles, face), since treating tinea as psoriasis with a topical corticosteroid can worsen a fungal infection.

Treatment Targets

Achieve clear or almost-clear skin and durable, long-term disease control — not just partial improvement.
Relieve itch, pain, and physical discomfort from active plaques.
Improve health-related quality of life, including the psychosocial and occupational impact of visible skin disease.
Select therapy that also controls joint disease whenever psoriatic arthritis is present, rather than treating skin and joints as separate problems.
Minimize treatment-related adverse effects, matching therapy intensity to disease severity and to the individual patient's risk profile and preferences.
Screen for and manage the comorbidities associated with psoriasis (cardiovascular risk factors, metabolic syndrome, depression/anxiety, inflammatory bowel disease), particularly in moderate-to-severe disease.
Promptly identify and refer patients with severe, treatment-resistant, or emergency-pattern psoriasis (erythrodermic, generalized pustular) to a dermatologist.

Choose Initial Treatment

The 4 treatment tracks, by severity

Topical therapy

First-line for mild-to-limited disease — under about 3% BSA, without special-site involvement that is inadequately controlled, and without a significant quality-of-life impact. The foundation of therapy even for many patients also receiving phototherapy or a systemic agent.

Phototherapy

For localized-to-widespread plaque psoriasis inadequately controlled with topical therapy alone, when accessible — narrow-band UVB (NB-UVB) is the established, most commonly used modality. Requires dermatology-supervised administration and a substantial time commitment (typically 3 to 5 sessions weekly).

Conventional systemic therapy

Methotrexate, acitretin, cyclosporine, apremilast, or deucravacitinib for moderate-to-severe disease — BSA over 10%, or any BSA with a special site inadequately controlled by topical therapy, or significant quality-of-life impact — when phototherapy is inaccessible, impractical, or has failed, or when disease severity or psoriatic arthritis makes a biologic-level agent more appropriate but is not yet accessible or desired.

Biologic therapy

TNF-alpha, IL-17, IL-23, or IL-12/23 inhibitors for moderate-to-severe disease meeting the same threshold as conventional systemic therapy, and preferentially considered over conventional nonbiologic agents given superior average efficacy and, for most classes, a more favourable routine-monitoring burden — cost and access are the main practical barriers.^[5]

Direct treatment rule

Localized, mild-to-moderate disease (under about 3% BSA, non-special site) start a moderate-to-high-potency topical corticosteroid, or a topical corticosteroid combined with a vitamin D analogue (calcipotriol/betamethasone), applied once or twice daily for 4 to 8 weeks.^[6]

Scalp psoriasis start a moderate-to-ultra-high-potency topical corticosteroid (lotion, solution, gel, or foam vehicle for ease of application) once daily for 4 to 8 weeks; add a vitamin D analogue if response is inadequate, and use a keratolytic shampoo (coal tar and/or salicylic acid) just before the corticosteroid if scale is significant.^[6]

Face or fold (intertriginous) psoriasis start low-potency hydrocortisone twice daily, since these are the thinnest-skinned, most atrophy-prone sites — reserve a stronger topical corticosteroid for short-term flares only (2 to 4 weeks). Topical roflumilast, tacrolimus, or pimecrolimus are steroid-sparing options for longer-term or maintenance use at these sites, particularly given the atrophy risk of repeated corticosteroid courses.^[6] Topical vitamin D analogues are also a reasonable option at this site, with a favourable long-term safety profile for maintenance use.^[7]

Palm and sole (palmoplantar) psoriasis start an ultra-high-potency topical corticosteroid, often needed given the thickness and treatment-resistance of skin at this site; add a vitamin D analogue, coal tar, salicylic acid, or tazarotene if response is inadequate.^[6]

Topical therapy inadequate after 1 to 2 months, or disease that is over 10% BSA, involves a special site not controlled by topical therapy, or has a significant quality-of-life impact refer for phototherapy (if accessible) or start a systemic agent — these patients are candidates for systemic therapy regardless of the precise BSA percentage.^[3]

Choosing among systemic options a biologic agent is generally preferable to a conventional nonbiologic systemic agent on efficacy and monitoring-burden grounds where accessible; methotrexate remains a reasonable, cost-effective first systemic choice when a biologic is not accessible, not desired, or not yet indicated.^[5]

Psoriatic arthritis is present choose an agent with established efficacy for both skin and joint disease rather than treating them separately — a TNF-alpha inhibitor or an IL-17 inhibitor is first-line across all 6 psoriatic arthritis domains (peripheral arthritis, axial disease, enthesitis, dactylitis, skin, and nail disease); an IL-23 inhibitor is a reasonable option for peripheral arthritis, enthesitis, dactylitis, skin, and nail disease but has weaker evidence specifically for axial spine involvement.^[2]

Before starting any biologic, or apremilast/deucravacitinib/cyclosporine in a patient with risk factors for latent infection complete tuberculosis screening (TST or IGRA, with chest x-ray if positive), hepatitis B and C screening, and confirm vaccinations are up to date — do not start immunosuppressive or biologic therapy before this is done (see Monitoring & Follow-Up).^[5]

Do not escalate topical corticosteroid potency indefinitely, or continue an ultra-high-potency agent long-term on the face or in skin folds, or as maintenance therapy anywhere — step down to a lower potency, a non-steroid topical, or systemic therapy once control is achieved or if a higher-potency trial has failed.

Non-Pharmacologic Treatment

Regular use of a nonirritating, fragrance-free moisturizer hydrates plaques and reduces itching and scaling; thicker vehicles (ointments and creams) are more effective than lotions at hydrating skin and providing a barrier against irritants. Apply the medicated topical product first, then the moisturizer.
Wash the scalp at least 2 to 3 times weekly with a nonirritating, fragrance-free shampoo to help moisturize and remove scale debris; applying shampoo to dry hair and scalp before adding water can improve removal of oil-based medicated scalp preparations.
Minimize skin trauma (scratching, aggressive manicures/pedicures, tight or occlusive clothing) to reduce Koebnerization; keep nails trimmed short.
In fold areas specifically, minimize friction and occlusion, wear loose-fitting clothing, and use moisture-wicking fabrics to reduce irritation, maceration, and Koebnerization.
Support smoking cessation and moderation of alcohol intake — both are associated with increased disease severity.
Encourage a healthy weight — obesity is associated with increased severity and reduced treatment response.
Address the substantial nonadherence problem with topical therapy directly: ask about cost, inconvenience, time burden, and cosmetic acceptability of the specific vehicle prescribed, and adjust the regimen (e.g., switching a cream to an ointment for better efficacy on thick plaques, or to a lotion/foam for easier application to hair-bearing areas) rather than assuming nonadherence reflects poor motivation.
Phototherapy: narrow-band UVB (NB-UVB) is the established, most commonly used phototherapy modality for psoriasis inadequately controlled by topical therapy, given its convenience (no photosensitizing agent needed) and favourable safety profile relative to PUVA (psoralen plus UVA), which carries an increased long-term skin-malignancy risk. Administered under dermatology supervision, typically 3 to 5 sessions weekly; can be combined with topical agents. Requires a substantial ongoing time commitment, which is the main practical barrier to its use.^[8]

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Hydrocortisone Preferred	1st line for face and skin folds	Apply once or twice daily for up to about 4 weeks	Mild irritation, dryness	Preferred initial strength for thin-skinned, atrophy-prone sites; step down or stop once controlled.
Betamethasone (moderate-to-high potency) Preferred	1st line for trunk, extremities, and palmoplantar disease	Apply once or twice daily for 4-8 weeks	Skin thinning, striae, telangiectasia with prolonged use	Do not use long-term on the face or in skin folds; step down once controlled.
Clobetasol propionate (ultra-high potency) Special situation	Scalp or palmoplantar psoriasis inadequately controlled by lower potency	Apply once or twice daily; do not exceed 50 g/week; brief courses only	Skin atrophy, striae, HPA-axis suppression with prolonged or extensive use	Not for the face, groin, or axillae; never a maintenance agent.
Calcipotriol Alternative	Adjunct or alternative to a topical corticosteroid, trunk/extremities	Apply twice daily	Local skin irritation	Combine with, or alternate with, a topical corticosteroid; not for the face or folds.
Calcipotriol / betamethasone Preferred	Combination topical, often more effective than either component alone	Apply once daily (on the scalp: at bedtime, wash out in the morning)	Local skin irritation	A reasonable initial choice when corticosteroid monotherapy alone has been inadequate; not for the face or folds.
Tazarotene Alternative	Adjunct for palmoplantar or nail psoriasis, or trunk/extremities	Apply once daily, generally in the evening	Local irritation, photosensitivity	Often combined with a topical corticosteroid to offset irritation; avoid in pregnancy.
Roflumilast Alternative	Steroid-sparing option, including face and fold areas	Apply once daily	Application-site burning/stinging; diarrhea, headache (uncommon)	No corticosteroid-type atrophy risk — a useful long-term option at sensitive sites.
Tacrolimus (topical) Special situation	Off-label steroid-sparing option for face and fold psoriasis	Apply twice daily	Application-site burning, stinging	Health Canada-approved for atopic dermatitis, not psoriasis — an established but off-label use at atrophy-prone sites.
Methotrexate Preferred	1st conventional systemic option; effective for skin and joints	7.5-25 mg PO, SC, or IM once weekly, with folic acid	Bone marrow suppression, hepatotoxicity, GI effects, pulmonary toxicity	Contraindicated in pregnancy and active liver disease; a weekly, not daily, dose — confirm the patient understands this.
Acitretin Special situation	Nonimmunosuppressive option, particularly for palmoplantar or pustular/erythrodermic variants	10-75 mg PO once daily	Mucocutaneous dryness, hyperlipidemia, hepatotoxicity, teratogenicity	Effective contraception required 1 month before, throughout, and for 3 years after stopping in anyone who could become pregnant.
Cyclosporine Special situation	Rapid-acting option for acute, severe flares	2.5-5 mg/kg/day PO	Hypertension, nephrotoxicity, hyperlipidemia	Not recommended continuously beyond about 1 year given cumulative nephrotoxicity; monitor blood pressure and renal function closely.
Apremilast Alternative	Oral option with a favourable routine-safety profile	Titrate over 5 days to 30 mg PO twice daily	Diarrhea, nausea, headache, weight loss	No routine bloodwork monitoring required — a reasonable choice for medically complex patients wanting to avoid injections.
Deucravacitinib Alternative	Oral TYK2 inhibitor, more effective than apremilast in head-to-head trials	6 mg PO once daily	Upper respiratory infection, herpes simplex reactivation, acneiform rash, folliculitis	Avoid in severe hepatic impairment or active infection; long-term real-world experience is still accumulating.
Adalimumab (TNF-alpha inhibitor) Preferred	1st-line biologic; effective for skin, joints, and most psoriatic arthritis domains	80 mg SC, then 40 mg SC every 2 weeks starting 1 week after the initial dose	Injection-site reactions, infection risk, rare demyelinating events	Relative contraindications: multiple sclerosis/other demyelinating disease, significant heart failure.
Secukinumab (IL-17 inhibitor) Preferred	1st-line biologic; among the most effective classes for skin clearance	300 mg SC weekly for 5 doses, then 300 mg SC monthly	Nasopharyngitis, upper respiratory infection, mucocutaneous candidiasis	Avoid, or use with caution, in active or strongly suspected inflammatory bowel disease — this class can trigger or worsen IBD.
Guselkumab (IL-23 inhibitor) Preferred	Biologic option with an infrequent, every-8-week maintenance schedule	100 mg SC at weeks 0 and 4, then every 8 weeks	Injection-site reactions, upper respiratory infection	Strong skin and peripheral-joint efficacy; weaker evidence specifically for the axial-spine domain of psoriatic arthritis than TNF-alpha or IL-17 inhibitors.
Ustekinumab (IL-12/23 inhibitor) Alternative	Biologic option with a quarterly maintenance schedule	45 mg SC at weeks 0 and 4, then every 12 weeks (90 mg if over 100 kg)	Nasopharyngitis, upper respiratory infection, headache	Longest real-world safety track record of the biologic classes; generally less effective on average than IL-17/IL-23 inhibitors for skin clearance.

Biologics by class: current comparative evidence and selection factors

TNF-alpha inhibitors

Adalimumab, certolizumab pegol, etanercept, infliximab. The longest track record among the biologic classes, with the most reassuring pregnancy data. Effective across all psoriatic arthritis domains, including axial disease. Relative contraindications: multiple sclerosis or other demyelinating disease, and significant heart failure.

IL-17 inhibitors

Bimekizumab, brodalumab, ixekizumab, secukinumab. Among the most effective classes for skin clearance in current network meta-analyses, and effective across all psoriatic arthritis domains including axial disease.^[9] Relative contraindication: active or strongly suspected inflammatory bowel disease, which this class can trigger or worsen — an IL-23 or TNF-alpha inhibitor is generally preferred when IBD is a concern. Mucocutaneous candidiasis is a class-associated adverse effect. Brodalumab carries a specific warning regarding suicidal ideation and behaviour and requires the prescriber and pharmacist to follow the enrolment/monitoring process specified in its Canadian product monograph.

IL-23 inhibitors

Guselkumab, risankizumab, tildrakizumab. Strong skin-clearance efficacy with an infrequent (every 8-to-12-week) maintenance schedule, an advantage for adherence. Effective for peripheral arthritis, enthesitis, dactylitis, and nail disease, but with weaker evidence specifically for the axial-spine domain of psoriatic arthritis than TNF-alpha or IL-17 inhibitors — a TNF-alpha or IL-17 inhibitor is generally preferred when axial disease is present.^[2] Guselkumab and risankizumab also have inflammatory bowel disease indications, making this class a reasonable choice when concomitant IBD is a concern.

IL-12/23 inhibitor

Ustekinumab. The longest real-world safety experience among current biologics, and a quarterly maintenance schedule. Generally less effective on average for skin clearance than the IL-17 and IL-23 inhibitor classes in current comparative evidence, though it remains a reasonable option, including when IBD is a concern.^[9]

Special Populations

Pregnancy

Psoriasis itself often improves during pregnancy, though a minority of patients worsen, and the disease course cannot be predicted in advance. For patients with mild disease, many clinicians favour stopping nonessential therapy during pregnancy; for moderate-to-severe or unstable disease, or when psoriatic arthritis is present, stopping treatment altogether is often not practical, and topical therapy is preferred whenever it can achieve control.^[1]

Topical corticosteroids remain a core option throughout pregnancy — low- and moderate-potency agents are preferred over higher-potency agents where adequate.
Topical vitamin D analogues (calcipotriol, calcitriol) have not been formally established as safe in pregnancy, but systemic absorption of topical calcipotriol is low and clinically significant effects are considered unlikely.
Topical tazarotene is not recommended in pregnancy given its retinoid class.
Coal tar and anthralin have measurable systemic absorption; no adverse fetal effects have been consistently reported, but avoid extensive use given limited safety data.
NB-UVB phototherapy is considered the safest option for widespread psoriasis in pregnancy that is not controlled by topical therapy alone.^[8]
Methotrexate and acitretin are contraindicated in pregnancy — both are teratogenic (see Pre-Pregnancy Planning below).
Cyclosporine is not associated with adverse outcomes in the transplant-patient literature; reserve for severe disease in pregnancy, at the minimal effective dose.
Apremilast and deucravacitinib have limited human pregnancy data, and risk is difficult to assess — avoid unless no adequate alternative exists.
TNF-alpha inhibitors have the most reassuring pregnancy safety data among the biologics; certolizumab pegol has minimal to no placental transfer in the third trimester and is generally preferred when a biologic is needed close to delivery, while adalimumab, etanercept, and infliximab do cross the placenta (increasingly in the third trimester), with a theoretical concern for neonatal immunosuppression — discuss live-vaccine timing for the infant with the treating team when one of these was used in pregnancy.^[5]
IL-17, IL-23, and IL-12/23 inhibitors have limited pregnancy data, and risk is difficult to assess — weigh the benefit of disease control carefully against this uncertainty with the patient.

Pre-pregnancy planning

Methotrexate must be stopped at least 3 months before attempting conception, by both the person who will carry the pregnancy and their partner if also taking methotrexate — though limited evidence suggests paternal low-dose methotrexate exposure near conception has not been associated with adverse pregnancy or fetal outcomes.
Acitretin requires effective contraception starting 1 month before treatment, continuing throughout treatment, and for at least 3 years after stopping, in anyone who could become pregnant — avoid alcohol during treatment and for a similar interval afterward, since alcohol promotes conversion of acitretin to etretinate, a longer-acting teratogen that can persist in the body for years. No waiting period is required before conception in a person who takes acitretin and produces sperm.

Breastfeeding

Avoid direct contact between an infant's skin or mouth and any body area treated with a topical product.
Avoid coal tar given infant absorption risk via skin-to-skin or skin-to-mouth contact.
Topical corticosteroids carry low risk to a breastfeeding infant except with extensive use of the most potent agents.
Topical calcineurin inhibitors (tacrolimus, pimecrolimus) have minimal systemic absorption and can be used.
Methotrexate and acitretin are avoided while breastfeeding given their inherent toxicity, despite low transfer into breast milk.
Cyclosporine transfers into breast milk in small amounts; use is generally avoided while breastfeeding.
Apremilast and deucravacitinib transfer into breast milk is unknown; use is not recommended while nursing.
Certolizumab pegol shows minimal to no transfer into breast milk and is considered acceptable while breastfeeding by most experts. Other biologics are large molecules with low expected transfer, but caution is advised, especially with a newborn or preterm infant, until more data accumulate.

Pediatrics

This chapter focuses on adult plaque psoriasis. Topical therapy remains first-line in children, generally using lower-potency corticosteroids and shorter courses given a higher skin-surface-to-body-mass ratio and greater systemic absorption risk. Several biologics carry a Health Canada-approved pediatric indication for moderate-to-severe plaque psoriasis (including etanercept, ustekinumab, secukinumab, and ixekizumab, subject to age-specific approval) — a child or adolescent who is a candidate for phototherapy or a systemic/biologic agent should be managed together with a pediatric dermatologist rather than dosed by extrapolation from adult regimens.

Renal and hepatic impairment

Methotrexate is contraindicated in significant renal impairment and active liver disease, and requires more frequent monitoring in mild-moderate impairment.
Cyclosporine is nephrotoxic — avoid in pre-existing significant renal impairment and monitor renal function closely during use.
Acitretin requires monitoring of liver enzymes given hepatotoxicity risk; use with caution in hepatic impairment.
Apremilast requires a reduced dose (10 mg once daily) in severe renal impairment (creatinine clearance under 30 mL/min).
Deucravacitinib should be avoided in severe hepatic impairment; active infection is also a reason to avoid starting it.
Most biologics are not renally or hepatically dose-adjusted, but active infection and organ function should be reconfirmed before every dose.

Monitoring & Follow-Up

Response assessment

Reassess topical therapy for adequate response after 4 to 8 weeks; question the diagnosis, rather than simply escalating potency again, if there has been no meaningful improvement within 1 to 2 months of an optimally applied regimen.^[6] For systemic and biologic agents, assess response at the interval standard for that agent — most biologics show a meaningful response by 12 to 16 weeks, and a lack of any response by that point should prompt a switch rather than an extended trial.

Baseline and ongoing labs by drug class

Methotrexate: baseline CBC, liver enzymes, renal function, and hepatitis B/C serology; repeat CBC and liver enzymes periodically (commonly every 2 to 4 weeks initially, then every 8 to 12 weeks once stable) for the duration of therapy.
Acitretin: baseline and periodic fasting lipid profile, liver enzymes, and renal function.
Cyclosporine: baseline and regular blood pressure and renal function — do not let serum creatinine rise more than about 30% above baseline without dose reduction or discontinuation; monitor lipids periodically. Not recommended for continuous use beyond about 1 year given cumulative nephrotoxicity risk; intermittent courses are preferred.^[3]
Apremilast: no routine bloodwork monitoring is required.
Deucravacitinib: no routine bloodwork monitoring is specifically mandated, though standard infection vigilance applies.
Biologics (all classes): baseline tuberculosis screening (TST or IGRA, with chest x-ray if positive), hepatitis B and C serology, and confirmation that vaccinations are current before starting; ongoing vigilance for infection at every visit rather than routine repeat bloodwork for most agents.^[5]

Vaccination

Confirm vaccinations are up to date before starting an immunosuppressive or biologic agent wherever possible. Inactivated vaccines (including recombinant zoster vaccine) can be given safely during immunosuppressive or biologic therapy, though the immune response may be somewhat reduced. Avoid live-attenuated vaccines (MMR, varicella, live zoster, yellow fever, live oral typhoid, live intranasal influenza) during methotrexate, cyclosporine, apremilast, deucravacitinib, or biologic therapy.^[10]

Psoriatic arthritis screening

Screen every psoriasis patient without a known psoriatic arthritis diagnosis at least annually using the PEST questionnaire (see Assessment & Diagnosis) — refer to rheumatology for a score of 3 or more, or for any new, persistent joint symptoms regardless of score.^[2]

Comorbidity screening

Screen for cardiovascular risk factors, metabolic syndrome, diabetes, and depression/anxiety, particularly in moderate-to-severe disease — consider earlier and more frequent screening in this group given the higher comorbidity burden.^[1]

Treatment Failure / Next Step

Confirm adherence and correct application technique before assuming a topical agent has failed — ask specifically about frequency, amount used, and vehicle acceptability, since poor adherence is a well-documented, common, and reversible cause of apparent topical failure.
Reconfirm the diagnosis — reconsider the differential-diagnosis tables in Assessment & Diagnosis if response is genuinely inadequate despite confirmed adherence to an appropriate regimen.
Increase topical corticosteroid potency, or add/switch to a second topical class (vitamin D analogue, tazarotene, coal tar, or roflumilast) if response remains inadequate after 4 to 8 weeks of an appropriately potent agent.
If topical therapy at maximal reasonable intensity is still inadequate, or the disease has crossed the systemic-therapy threshold (over 10% BSA, an inadequately controlled special site, or significant quality-of-life impact), refer for phototherapy if accessible, or start a conventional systemic agent or biologic.
If a conventional nonbiologic systemic agent (methotrexate, acitretin, cyclosporine, apremilast, deucravacitinib) is inadequate at an appropriate dose and duration, move to a biologic.
If a first biologic is inadequate after an appropriate trial (commonly 12 to 16 weeks), switch to a biologic with a different mechanism of action rather than cycling within the same class, particularly after failure of a TNF-alpha inhibitor.^[9]
At any point, actively ask about new joint symptoms — inadequate skin response combined with new joint complaints may mean the current agent, however good for skin, is not adequately controlling the joint domain, and a switch to an agent with established efficacy across both domains (TNF-alpha or IL-17 inhibitor) should be considered.^[2]
Refer to dermatology for any patient with recalcitrant disease despite an adequate systemic or biologic trial, disease at a cosmetically or functionally sensitive site not responding to standard measures, or a presentation raising concern for erythrodermic or generalized pustular psoriasis.

Common Errors to Avoid

Stopping a long course of a potent topical corticosteroid, or systemic corticosteroid therapy for another condition, abruptly in a patient with psoriasis — can precipitate a rebound flare or generalized pustular psoriasis.
Using an ultra-high- or high-potency topical corticosteroid long-term on the face or in skin folds — these sites are the most prone to atrophic change, and a lower-potency agent or a non-steroid topical (roflumilast, tacrolimus, pimecrolimus) should be used for anything beyond a short flare.
Never screening for psoriatic arthritis, or only asking generally about joint pain instead of using a structured tool — many patients do not spontaneously report joint symptoms or connect them to their skin disease.
Starting a biologic, or apremilast/deucravacitinib/cyclosporine in a patient with infection risk factors, without completing tuberculosis and hepatitis B/C screening first.
Giving a live vaccine to a patient on methotrexate, cyclosporine, apremilast, deucravacitinib, or a biologic, instead of confirming vaccination status before starting therapy.
Treating fold-area or facial psoriasis as if it were trunk/extremity psoriasis — these sites need lower topical corticosteroid potency and different adjuncts (see Choose Initial Treatment) given their higher atrophy risk.
Missing tinea or candidiasis at a fold or palmoplantar site and treating it as psoriasis with a topical corticosteroid, which can worsen an untreated fungal infection — confirm with a KOH scraping or fungal culture when there is any doubt.
Choosing a TNF-alpha inhibitor in a patient with multiple sclerosis, another demyelinating disease, or significant heart failure — both are relative contraindications for this class.
Choosing an IL-17 inhibitor in a patient with active or a strong history of inflammatory bowel disease — this class can trigger new-onset or worsen existing IBD; an IL-23 inhibitor or TNF-alpha inhibitor is generally preferred in this situation.
Exceeding the weekly maximum dose of an ultra-high-potency topical corticosteroid (commonly 50 g/week in adults), or continuing it well beyond the 4-to-8-week window it was intended for.
Forgetting comorbidity screening (cardiovascular risk factors, metabolic syndrome, depression/anxiety) in a patient with moderate-to-severe disease — psoriasis is a systemic disease, not just a skin disease.
Assuming a topical calcineurin inhibitor (tacrolimus, pimecrolimus) is on-label for psoriasis — it is Health Canada-approved for atopic dermatitis, and its use in psoriasis (most often at the face and folds) is an established but off-label practice; counsel and document accordingly.

Clinical Decision Algorithm

Algorithm A — overall assessment and severity triage

Confirmed or suspected plaque psoriasis

Assess for erythrodermic or generalized pustular features, signs of infection on immunosuppressive therapy, and new joint symptoms (see Red Flags & Refer)

Red flags present

Manage as a dermatologic emergency or urgent referral — do not proceed with routine stepwise topical therapy

No red flags

Estimate BSA and site involvement; screen for psoriatic arthritis with PEST

Localized, under about 3% BSA, non-special site

Proceed to Algorithm B — topical therapy pathway

Over 10% BSA, an inadequately controlled special site, significant quality-of-life impact, or psoriatic arthritis present

Proceed to Algorithm C — phototherapy, conventional-systemic, and biologic pathway

Algorithm B — topical therapy pathway, by body site

Localized, mild-to-moderate plaque psoriasis

Scalp

Moderate-to-ultra-high-potency topical corticosteroid once daily for 4-8 weeks, +/- a vitamin D analogue

Maintenance: taper to 2-3 times weekly, or switch to a non-steroid topical

Face or skin folds

Hydrocortisone (low potency) twice daily, or roflumilast/tacrolimus/pimecrolimus for longer-term use

Avoid ultra-high-potency corticosteroids long-term at this site

Trunk or extremities

Moderate-to-ultra-high-potency topical corticosteroid, +/- calcipotriol/betamethasone

Step down to a lower potency once controlled

Palms, soles, or nails

Ultra-high-potency topical corticosteroid, +/- a vitamin D analogue, tazarotene, coal tar, or salicylic acid

One of the most treatment-resistant sites — lower threshold for phototherapy or systemic referral

Inadequate response after 1 to 2 months at any site: proceed to Algorithm C

Algorithm C — phototherapy, conventional-systemic, and biologic pathway

Systemic-therapy threshold met: over 10% BSA, an inadequately controlled special site, significant quality-of-life impact, or psoriatic arthritis present

Phototherapy accessible, and no urgent need for a systemic agent

Narrow-band UVB phototherapy, 3 to 5 sessions weekly under dermatology supervision^[8]

Phototherapy inaccessible, impractical, or inadequate

Complete tuberculosis and hepatitis B/C screening; confirm vaccinations are current

No psoriatic arthritis, biologic accessible

Start a biologic (TNF-alpha, IL-17, or IL-23 inhibitor, selected by comorbidity profile) — see Pharmacologic Treatment Options

Psoriatic arthritis present

Start a TNF-alpha or IL-17 inhibitor (1st line across all 6 psoriatic arthritis domains); an IL-23 inhibitor is an option if axial disease is not a concern^[2]

Biologic not accessible or not desired

Start methotrexate (1st conventional systemic choice), or acitretin, cyclosporine, apremilast, or deucravacitinib, matched to patient comorbidities

Inadequate response after 12 to 16 weeks (biologic) or an appropriate conventional-agent trial: switch to a different mechanism of action rather than repeating the same class — see Treatment Failure / Next Step

Drug Tables

How to use this table: doses are adult doses and require patient-specific confirmation, including renal/hepatic adjustment. Select any drug name to open its complete Pharmasist Drug Database page.

Phototherapy (non-drug)

Narrow-band UVB (NB-UVB) is the established, most commonly used phototherapy modality for psoriasis inadequately controlled by topical therapy — preferred over psoralen-plus-UVA (PUVA) given greater convenience and a more favourable long-term safety profile; PUVA carries an increased skin-malignancy risk with cumulative use. Administered under dermatology supervision, typically 3 to 5 sessions weekly, and can be combined with topical agents such as coal tar, anthralin, a vitamin D analogue, a topical corticosteroid, or tazarotene. Length of remission is longest with phototherapy among available options, though it is not a cure.

Topical corticosteroids, by potency

The mainstay of therapy for localized disease. Use the lowest potency that controls the site being treated; step down or stop once control is achieved rather than continuing indefinitely.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Hydrocortisone (low potency)	Face / folds: Apply once or twice daily for up to about 4 weeks	Mild irritation, dryness, folliculitis; lower atrophy risk than higher potencies	Concurrent use of other corticosteroid-containing products adds to total exposure	Preferred initial strength for the face and skin folds, where atrophy risk is highest.
Betamethasone (moderate-to-high potency)	Trunk / extremities: Apply once or twice daily for 4-8 weeks Palms / soles: Apply once or twice daily; a higher potency within this range or a stronger agent is often needed given skin thickness	Skin thinning, striae, telangiectasia, acneiform eruptions with prolonged use	Concurrent use of other corticosteroid-containing products adds to total exposure	1st-line potency range for trunk, extremities, and palmoplantar disease.
Mometasone (high potency)	Face / scalp / axillae: Apply once daily; maximum 5 days Body: Apply once daily; maximum 3 weeks	Burning, stinging, dryness; HPA-axis suppression with extensive/prolonged use	Concurrent use of other corticosteroid-containing products adds to total exposure	Lotion vehicle is well suited to the scalp.
Clobetasol propionate (ultra-high potency)	Scalp / palms / soles: Apply once or twice daily; do not exceed 50 g/week; brief courses only	Skin atrophy, striae, HPA-axis suppression, rare rebound pustular flare on withdrawal	Concurrent use of other corticosteroid-containing products adds to total exposure	Reserve for scalp or palmoplantar disease inadequately controlled by a lower potency; not for the face, groin, or axillae; never a maintenance agent.

Vitamin D analogues

A nonsteroidal option for the trunk and extremities; not for the face or folds.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Calcipotriol	Body: Apply twice daily	Local skin irritation	None significant at topical doses	Often alternated with, or combined with, a topical corticosteroid for better tolerability.
Calcitriol	Body: Apply twice daily	Local skin irritation	None significant at topical doses	An alternative vitamin D analogue; labelled for mild-to-moderate disease involving up to about 35% BSA.

Vitamin D analogue / corticosteroid combination

Drug	Dosage	Adverse effects	Drug interactions	Comments
Calcipotriol / betamethasone	Body: Apply once daily Scalp: Apply once daily at bedtime; wash out in the morning	Local skin irritation	Concurrent use of other corticosteroid-containing products adds to total exposure	Often more effective than either component alone; a reasonable initial choice for trunk/extremity disease inadequately controlled by a corticosteroid alone. Manufacturer-labelled treatment duration ranges from 4-8 weeks depending on the product, though longer courses are used in practice under supervision.

Topical retinoid, and retinoid/corticosteroid combination

Drug	Dosage	Adverse effects	Drug interactions	Comments
Tazarotene	Body / palms / soles / nails: Apply once daily, generally in the evening	Local irritation, photosensitivity	None significant at topical doses	Often combined with a topical corticosteroid to offset irritation; contraindicated in pregnancy. Under occlusion for about 12 weeks has been used specifically for nail psoriasis.
Halobetasol propionate / tazarotene	Body: Apply once daily	Corticosteroid: burning, itching, skin atrophy, striae. Retinoid: skin irritation	Concurrent use of other corticosteroid-containing products adds to total exposure	Indicated for the body; contraindicated on the face and in skin folds.

Topical phosphodiesterase-4 (PDE4) inhibitor

Drug	Dosage	Adverse effects	Drug interactions	Comments
Roflumilast	Body / face / folds: Apply once daily	Application-site burning/stinging (uncommon); diarrhea, nausea, headache	None significant at topical doses	No corticosteroid-type atrophy risk — indicated for plaque psoriasis including fold areas, and a useful longer-term option at atrophy-prone sites.

Topical calcineurin inhibitors

Health Canada-approved for atopic dermatitis; use in psoriasis is an established but off-label practice, particularly at the face and folds given no atrophy risk with extended use.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Tacrolimus	Face / folds: Apply twice daily	Application-site burning, stinging	None significant at topical doses	No risk of cutaneous atrophy — useful for longer-term maintenance at thin-skinned sites.
Pimecrolimus	Face / folds: Apply twice daily	Application-site burning, stinging	None significant at topical doses	Alternative topical calcineurin inhibitor with the same off-label rationale as tacrolimus.

Keratolytic agents, and corticosteroid/keratolytic combination

Adjuncts that remove scale and improve penetration of a co-applied corticosteroid or vitamin D analogue — not stand-alone treatments for the inflammatory component of psoriasis.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Salicylic acid	Cream / lotion / gel: Apply once or twice daily Shampoo: Apply once or twice weekly	Local irritation, scaling; salicylate toxicity with prolonged use over large areas, especially in children	Theoretical additive salicylate exposure with high-dose oral salicylate use over large treated areas	Flattens thick, scaly plaques and treats palmoplantar hyperkeratosis; limit surface area and duration, particularly in children.
Betamethasone dipropionate / salicylic acid	Body: Apply once or twice daily	Corticosteroid: burning, itching, skin atrophy, striae. Keratolytic: erythema, local irritation	Concurrent use of other corticosteroid-containing products adds to total exposure	Combines keratolytic scale removal with corticosteroid anti-inflammatory effect in one product.

Tars and anthracene derivatives

Older, effective, inexpensive options whose use has declined mainly due to odour, staining, and the resulting adherence problems with the chronic treatment psoriasis needs.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Coal tar	Shampoo: Apply to wet scalp/hair, leave on as directed, then rinse, 2-3 times weekly Ointment / lotion / gel: Apply once daily	Skin irritation, folliculitis, photosensitivity; malodour and staining of skin/hair/fabric	Additive photosensitivity with other photosensitizing medications and with phototherapy	Not for use in skin folds; can be combined with UVB phototherapy under dermatology supervision.
Anthralin	Body plaques: Apply once daily for the prescribed short-contact duration, then wash off completely	Irritation of surrounding normal skin; purple-brown staining of skin, hair, and fabric; transient staining of treated plaques	None significant	Modern short-contact regimens (apply for a limited period, then wash off) reduce irritation compared with older, longer-contact use. Not for the face, folds, or genital area.

Intralesional corticosteroid

Drug	Dosage	Adverse effects	Drug interactions	Comments
Triamcinolone	Localized plaques / nail bed: Injected by the treating clinician per lesion, spaced several weeks apart	Injection-site pain, local skin atrophy at the injection site	None significant	Used occasionally for localized, treatment-resistant plaques, and for nail-bed psoriasis; procedural pain often limits repeated use.

Adjunct topical antifungals (secondary candidiasis in fold areas)

Not psoriasis treatments themselves — added when a macerated or malodorous fold-area plaque suggests secondary candidal infection.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Clotrimazole	Fold areas: Apply twice daily	Local irritation	None significant	Combined with a low-potency topical corticosteroid when fold-area psoriasis appears secondarily infected with Candida.
Ketoconazole (topical)	Fold areas: Apply once or twice daily	Local irritation	None significant	Alternative topical antifungal for the same indication as clotrimazole.

Systemic nonbiologic agents

For moderate-to-severe disease inadequately controlled by topical therapy and phototherapy, or when phototherapy is inaccessible.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Methotrexate	Adults: 7.5-25 mg PO, SC, or IM once weekly, with folic acid co-administration	Bone marrow suppression, hepatotoxicity, GI effects, pulmonary toxicity, blood dyscrasias	Ethanol and acitretin increase the risk of methotrexate-induced liver injury; cholestyramine and colestipol can bind methotrexate in the gut; trimethoprim may increase bone marrow suppression; avoid live vaccines during therapy	Cost-effective, well-established 1st conventional systemic choice, effective for both skin and psoriatic arthritis. Avoid in pregnancy, active or chronic infection (including tuberculosis and hepatitis B/C), and significant liver disease; a weekly, not daily, dose.
Acitretin	Adults: 10-75 mg PO once daily	Arthralgia, myalgia, alopecia, mucocutaneous dryness, hyperlipidemia, hepatotoxicity, pseudotumor cerebri	Ethanol increases conversion to etretinate (a longer-acting teratogen); may increase methotrexate-induced liver injury risk; no clinically significant interaction with oral contraceptives, though the manufacturer states a progestin-only pill is not considered reliable during use	Nonimmunosuppressive — particularly useful for palmoplantar, pustular, or erythrodermic variants. Contraindicated in pregnancy; effective contraception required 1 month before, throughout, and for 3 years after stopping in anyone who could become pregnant.
Cyclosporine	Adults: 2.5-5 mg/kg/day PO	Hypertension, hyperlipidemia, renal dysfunction, tremor, headache, hypertrichosis	Extensively metabolized by CYP3A4 — many interactions (e.g., erythromycin, ketoconazole, rifampin, St. John's wort); avoid live vaccines during therapy	Rapid-acting option for acute, severe flares. Not recommended continuously beyond about 1 year given cumulative nephrotoxicity; monitor blood pressure and renal function closely, and do not let serum creatinine rise more than about 30% above baseline without dose reduction.
Apremilast	Titration, days 1-5: 10 mg AM (day 1); 10 mg AM/10 mg PM (day 2); 10 mg AM/20 mg PM (day 3); 20 mg AM/20 mg PM (day 4); 20 mg AM/30 mg PM (day 5) Maintenance (day 6 onward): 30 mg PO twice daily	Diarrhea, nausea, upper respiratory infection, headache, weight loss	Strong CYP3A4 inducers (rifampin, phenobarbital, carbamazepine, phenytoin) may reduce systemic concentration and efficacy; caution with live vaccines	Favourable routine-safety profile; no routine bloodwork monitoring required. Dose reduction to 10 mg once daily is required in severe renal impairment (creatinine clearance under 30 mL/min).
Deucravacitinib	Adults: 6 mg PO once daily, no titration required	Upper respiratory infection, herpes simplex reactivation, acneiform rash, folliculitis	Caution with live vaccines during therapy	An oral TYK2 inhibitor with superior efficacy to apremilast in head-to-head trials. Avoid in severe hepatic impairment and active infection; long-term real-world experience is still accumulating.

Biologic agents — TNF-alpha inhibitors

Effective across all 6 psoriatic arthritis domains including axial disease, with the most reassuring pregnancy safety data among the biologic classes. Relative contraindications: multiple sclerosis or other demyelinating disease; significant heart failure. Complete tuberculosis and hepatitis B/C screening and confirm vaccinations are current before starting any agent in this class; avoid live vaccines during therapy.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Adalimumab	Loading: 80 mg SC Maintenance: 40 mg SC every 2 weeks, starting 1 week after the loading dose	Injection-site reactions, serious infections, rare demyelinating events, rare malignancy	Possible increased serious-infection risk with concomitant immunosuppressives; methotrexate reduces adalimumab clearance	1st-line biologic option for chronic moderate-to-severe plaque psoriasis and psoriatic arthritis.
Etanercept	Initial: 50 mg SC twice weekly for 3 months Maintenance: 50 mg SC once weekly	Injection-site reactions, serious infections, autoimmune phenomena, worsening heart failure	Possible increased serious-infection risk with concomitant immunosuppressives; may enhance the neutropenic effect of sulfasalazine	Not for use in demyelinating disease; avoid in significant heart failure.
Infliximab	Loading: 5 mg/kg IV at weeks 0, 2, and 6 Maintenance: 5 mg/kg IV every 8 weeks thereafter	Infusion reactions, serious infections, hepatobiliary events, demyelinating disorders, rare lymphoma	Possible increased serious-infection risk with concomitant immunosuppressives	IV infusion, requiring an infusion setting; discontinue if an adequate response is not achieved by week 14.
Certolizumab pegol	Loading: 400 mg SC at weeks 0, 2, and 4 Maintenance: 200 mg SC every 2 weeks	Upper respiratory infection, headache, serious infections	Possible increased serious-infection risk with concomitant immunosuppressives	Minimal to no placental transfer in the third trimester — generally preferred TNF-alpha inhibitor when continued biologic therapy is needed close to delivery.

Biologic agents — IL-17 inhibitors

Among the most effective classes for skin clearance in current comparative evidence, and effective across all 6 psoriatic arthritis domains including axial disease. Relative contraindication: active or strongly suspected inflammatory bowel disease, which this class can trigger or worsen. Mucocutaneous candidiasis is a class-associated adverse effect. Complete tuberculosis and hepatitis B/C screening and confirm vaccinations are current before starting; avoid live vaccines during therapy.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Secukinumab	Loading: 300 mg SC (as 2 injections of 150 mg) weekly at weeks 0, 1, 2, 3, and 4 Maintenance: 300 mg SC every 4 weeks	Nasopharyngitis, upper respiratory infection, rhinitis, diarrhea, oral herpes, mucocutaneous candidiasis	Possible increased serious-infection risk with concomitant immunosuppressives	1st-line IL-17 inhibitor option.
Ixekizumab	Loading: 160 mg SC (as 2 injections of 80 mg) at week 0 Weeks 2-12: 80 mg SC every 2 weeks Maintenance: 80 mg SC every 4 weeks	Injection-site reactions, upper respiratory infection, mucocutaneous candidiasis	Possible increased serious-infection risk with concomitant immunosuppressives	Alternative IL-17 inhibitor with a similar efficacy and safety profile to secukinumab.
Bimekizumab	Loading: 320 mg SC (as 2 injections of 160 mg) every 4 weeks for the first 16 weeks Maintenance: 320 mg SC every 8 weeks	Oral candidiasis, upper respiratory infection, injection-site reactions, headache	Possible increased serious-infection risk with concomitant immunosuppressives	Dual IL-17A/IL-17F inhibitor with among the highest skin-clearance rates of any current biologic in comparative evidence; candidiasis risk is more prominent with this agent than with single-pathway IL-17 inhibitors.
Brodalumab	Loading: 210 mg SC at weeks 0, 1, and 2 Maintenance: 210 mg SC every 2 weeks	Headache, arthralgia, fatigue, oropharyngeal pain, diarrhea; suicidal ideation and behaviour (boxed warning)	Possible increased serious-infection risk with concomitant immunosuppressives	Carries a specific Canadian product-monograph warning regarding suicidal ideation and behaviour — follow the required prescriber/pharmacist enrolment and monitoring process before dispensing.

Biologic agents — IL-23 inhibitors

Strong skin-clearance efficacy with an infrequent maintenance schedule. Effective for peripheral arthritis, enthesitis, dactylitis, and nail disease, but weaker evidence for the axial-spine domain of psoriatic arthritis than TNF-alpha or IL-17 inhibitors. Guselkumab and risankizumab also have inflammatory bowel disease indications. Complete tuberculosis and hepatitis B/C screening and confirm vaccinations are current before starting; avoid live vaccines during therapy.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Guselkumab	Loading: 100 mg SC at weeks 0 and 4 Maintenance: 100 mg SC every 8 weeks	Injection-site reactions, upper respiratory infection	Possible increased serious-infection risk with concomitant immunosuppressives	1st-line IL-23 inhibitor option; every-8-week maintenance dosing after loading.
Risankizumab	Loading: 150 mg SC (as 2 injections of 75 mg) at week 0, repeated at week 4 Maintenance: 150 mg SC every 12 weeks	Upper respiratory infection, headache	Possible increased serious-infection risk with concomitant immunosuppressives	Every-12-week maintenance dosing after loading — among the least frequent dosing schedules of any biologic class.
Tildrakizumab	Loading: 100 mg SC at weeks 0 and 4 Maintenance: 100 mg SC every 12 weeks	Nasopharyngitis, upper respiratory infection, injection-site reactions, headache	Possible increased serious-infection risk with concomitant immunosuppressives	Alternative IL-23 inhibitor with a similar dosing interval to guselkumab.

Biologic agents — IL-12/23 inhibitor

The longest real-world safety experience among current biologics, with quarterly maintenance dosing. Generally less effective on average for skin clearance than the IL-17 and IL-23 inhibitor classes in current comparative evidence. Complete tuberculosis and hepatitis B/C screening and confirm vaccinations are current before starting; avoid live vaccines during therapy.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Ustekinumab	Loading (up to 100 kg): 45 mg SC at weeks 0 and 4 Loading (over 100 kg): 90 mg SC at weeks 0 and 4 Maintenance: Same dose every 12 weeks thereafter	Nasopharyngitis, upper respiratory infection, headache, injection-site reactions	Possible increased serious-infection risk with concomitant immunosuppressives	A reasonable option, including when concomitant inflammatory bowel disease is a concern.

References

Joint AAD-NPF guidelines of care for the management and treatment of psoriasis with awareness and attention to comorbidities — Journal of the American Academy of Dermatology (Elmets CA, Leonardi CL, Davis DMR, et al.). J Am Acad Dermatol 2019;80(4):1073-1113
Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA): updated treatment recommendations for psoriatic arthritis 2021 — Nature Reviews Rheumatology (Coates LC, Soriano ER, Corp N, et al.). Nat Rev Rheumatol 2022;18(8):465-479
Joint American Academy of Dermatology-National Psoriasis Foundation guidelines of care for the management of psoriasis with systemic nonbiologic therapies — Journal of the American Academy of Dermatology (Menter A, Gelfand JM, Connor C, et al.). J Am Acad Dermatol 2020;82(6):1445-1486
Evaluation of an existing screening tool for psoriatic arthritis in people with psoriasis and the development of a new instrument: the Psoriasis Epidemiology Screening Tool (PEST) questionnaire — Clinical and Experimental Rheumatology (Ibrahim GH, Buch MH, Lawson C, Waxman R, Helliwell PS). Clin Exp Rheumatol 2009;27(3):469-474
Joint AAD-NPF guidelines of care for the management and treatment of psoriasis with biologics — Journal of the American Academy of Dermatology (Menter A, Strober BE, Kaplan DH, et al.). J Am Acad Dermatol 2019;80(4):1029-1072
Joint AAD-NPF guidelines of care for the management and treatment of psoriasis with topical therapy and alternative medicine modalities for psoriasis severity measures — Journal of the American Academy of Dermatology (Elmets CA, Korman NJ, Prater EF, et al.). J Am Acad Dermatol 2021;84(2):432-470
Treatment of inverse/intertriginous psoriasis: updated guidelines from the medical board of the National Psoriasis Foundation — Journal of Drugs in Dermatology (Khosravi H, Siegel MP, Van Voorhees AS, Merola JF). J Drugs Dermatol 2017;16(8):760-766
Joint American Academy of Dermatology-National Psoriasis Foundation guidelines of care for the management and treatment of psoriasis with phototherapy — Journal of the American Academy of Dermatology (Elmets CA, Lim HW, Stoff B, et al.). J Am Acad Dermatol 2019;81(3):775-804
Systemic pharmacological treatments for chronic plaque psoriasis: a network meta-analysis — Cochrane Database of Systematic Reviews (Sbidian E, Chaimani A, Guelimi R, et al.). Cochrane Database Syst Rev 2025;2025(8):CD011535
Immunization of immunocompromised persons: Canadian Immunization Guide — Public Health Agency of Canada. Canadian Immunization Guide, Part 3

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.