Acute Rhinosinusitis

Clinical Snapshot

Acute rhinosinusitis is symptomatic inflammation of the nasal cavity and one or more paranasal sinuses, lasting 4 weeks or less.^[1] Most episodes are triggered by a viral upper respiratory tract infection; bacterial invasion of the sinuses complicates only 0.5-2% of adult cases and 6-13% of pediatric cases. The default management for uncomplicated acute rhinosinusitis is symptom control without antibiotics — about 70% of cases resolve within 2 weeks regardless of antibiotic use, and the 2025 AAO-HNSF guideline update recommends clinicians offer watchful waiting (not merely consider it) for uncomplicated disease with assured follow-up.^[2] Antibiotics do not reduce the rare risk of orbital or intracranial complications, so preventing complications is never, on its own, a reason to prescribe one.

Recognize the Condition

Categories, by duration

Acute

≤4 weeks — the focus of this chapter.

Subacute

4-12 weeks.

Chronic

≥12 weeks, may have acute exacerbations.

Recurrent

≥4 discrete episodes of acute rhinosinusitis per year, symptom-free between episodes.

Typical presentation — the PODS mnemonic (adults)

Pain (facial), particularly when bending forward.
Obstruction (nasal obstruction, blockage, congestion).
Discharge (purulent nasal drainage, anterior and/or posterior).
Smell disorder (reduced or lost sense of smell).

Patients may also have sore throat, cough, malaise, tooth pain, or fever. Children more often present with sudden onset of 2 or more of: discoloured nasal drainage, nasal obstruction, and/or cough (day or night).

Etiology

Most commonly triggered by rhinovirus, adenovirus, influenza, or parainfluenza virus, causing local inflammation, edema, mucus production, and sinus obstruction. In a small proportion of cases this permits bacterial invasion — Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella catarrhalis are the most common bacterial pathogens in both children and adults.

Differentiating from allergic rhinitis

Ask specifically about sneezing, watery rhinorrhea or watery/itchy eyes, and nasal or ocular pruritus — these point toward allergic rhinitis rather than rhinosinusitis. Sinus pain or headache without nasal symptoms should prompt consideration of dental disease or a primary headache syndrome instead.

Risk Factors

Recent viral upper respiratory tract infection.
Environmental irritant exposure, especially tobacco smoke.
Allergen exposure/allergic rhinitis.
Anatomic anomalies of the nasal cavity/sinuses.
Immunocompromise.
Pregnancy — hormone-induced nasal congestion and pregnancy-related immune changes raise the risk of bacterial rhinosinusitis roughly 6-fold versus the nonpregnant population, peaking in the second trimester; classic signs and symptoms are absent in nearly half of pregnant patients with confirmed purulent rhinosinusitis, so have a lower threshold to evaluate.

Red Flags & Refer

Refer/escalate urgently for evaluation of orbital or intracranial complications if any of the following are present, and refer to ENT for the additional criteria below:

Altered mental status.
Conjunctival or periorbital edema.
Exophthalmos (displaced globe).
Eyelid drop.
Impaired visual acuity or double vision.
Nausea and/or vomiting.
Neck stiffness.
Ocular pain or tenderness.
Ophthalmoplegia.
Restricted or painful extraocular movement.
Severe, intractable headache.
Swelling over the frontal bone.
The patient being systemically very unwell.
Refer to ENT for failure of second-line antibiotic therapy.
Refer to ENT for ≥4 episodes of bacterial rhinosinusitis per year.
Refer to ENT for anatomic anomalies of the nasal cavity/sinuses.
Refer to ENT for any of the complications above.

These findings tend to occur early in the illness course and are associated with severe symptoms — patients in whom a complication is suspected may need imaging (sinus x-ray, CT, or MRI) or endoscopically guided culture of sinus aspirate. Complications are rare in healthy individuals (roughly 1 in 12,000 children, 1 in 32,000 adults) but include orbital complications (most common overall, more frequent in children), intracranial complications (more frequent in adults under 40), and osseous complications (least common).

Assessment & Diagnosis

Diagnosis is clinical

Diagnosis relies on history with or without physical exam. Additional investigations are not needed in patients without features suggestive of complicated disease — radiography cannot distinguish viral from bacterial infection and is not recommended for routine diagnosis; nasal swabs are contaminated by normal flora and do not predict the true sinus pathogen; direct sinus aspiration is rarely performed outside of research or complicated cases.

The single most important diagnostic decision: viral or bacterial?

No individual symptom is diagnostic of bacterial involvement — fever occurs in both, and the colour of nasal discharge reflects the presence of neutrophils, not bacteria specifically. Diagnose acute bacterial rhinosinusitis based on the time course of illness, not the symptom pattern:

Symptoms of acute rhinosinusitis persisting without improvement for more than 10 days after URTI symptom onset, OR
Symptoms that worsen within 10 days after an initial period of improvement — "double sickening."

Severity classification (changes the escalation ladder)

Severe: at least 3 consecutive days of high fever (≥39°C) plus purulent nasal discharge or facial pain, especially in adults — this, or immunocompromise, moves a patient to a different (more aggressive) treatment tier regardless of the 10-day rule.

Examination

Posterior rhinoscopy may show nasal inflammation, mucosal edema, or purulent discharge; sinus tenderness may be present on palpation. Physical exam should specifically look for the red-flag findings above, which are more useful for excluding complications than for confirming the diagnosis itself.

Treatment Targets

Reduce symptoms.
Eradicate infection when bacterial and antibiotics are indicated.
Prevent recurrence.
Minimize unnecessary antibiotic use to limit resistance and adverse effects.

Choose Initial Treatment

Direct treatment rule

1st line, uncomplicated disease symptom management only, without antibiotics — this applies whether or not the patient meets criteria for acute bacterial rhinosinusitis, since even most bacterial cases resolve without treatment. Only 1 in 19 patients treated with an antibiotic experiences a faster cure than they would have without one (NNT = 19), while 1 in 8 experiences a side effect (NNH = 8).^[3]

Antibiotic-sparing option — intranasal corticosteroid trial for a patient who meets acute bacterial rhinosinusitis criteria (symptoms >10 days without improvement, or double sickening) but wants to avoid an antibiotic: a trial of high-dose intranasal corticosteroid, reassessed at 72 hours, with an antibiotic added if there is no improvement.

Antibiotic-sparing option — watchful waiting for the same patient: defer antibiotics for up to 7 days while managing symptoms, only appropriate when reassessment is guaranteed if illness persists or worsens. A delayed/backup prescription can support this approach.

Start an antibiotic now for severe presentation (≥3 consecutive days of high fever ≥39°C plus purulent discharge or facial pain), immunocompromise, or when symptom severity is significantly affecting quality of life (interfering with activity or sleep) and the patient prefers not to wait.

Non-Pharmacologic Treatment

Saline nasal irrigation — thins mucus, clears inflammatory mediators, improves mucociliary function, and moisturizes inflamed mucosa. No irrigation method has been shown clearly superior, though one adult study found large-volume irrigation (250 mL) more effective for rhinorrhea and postnasal drip than small-volume syringe irrigation (10 mL).
Comfort measures without formal efficacy data but commonly recommended: adequate rest and hydration, warm facial packs/compresses, sleeping with the head of the bed elevated.
Prevention: limit spread of viral infection (hand hygiene, and physical distancing/masking during a viral epidemic); avoid tobacco smoke and other environmental irritants; reduce allergen exposure.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Acetaminophen Preferred	Pain/fever control, all patients	Adults: 325-650 mg PO/PR Q4-6H PRN, max 4000 mg/day. Children: 10-15 mg/kg PO PRN Q4-6H, max 75 mg/kg/day	Uncommon at recommended dose; hepatotoxicity with overdose	Routine (not just PRN) use for the first 24-48 hours may help avoid unnecessary antibiotic requests.
Ibuprofen Preferred	Pain/fever control	Adults: 200-400 mg PO Q4-6H PRN, max 1200 mg/day self-care (2400 mg/day if supervised). Children >6mo: 5-10 mg/kg Q6-8H PRN, max 40 mg/kg/day	GI upset/bleeding; nephropathy; fluid retention	Avoid if dehydrated. Reduces effect of ACE inhibitors/beta-blockers/diuretics.
Intranasal corticosteroid (high-dose) Alternative	Antibiotic-sparing trial for mild-moderate ABRS	High-dose regimen equivalent to mometasone 400 mcg/day	Nasal burning/stinging, nosebleeds	Modest benefit only (NNT ~14); low doses are no better than placebo. Reassess at 72 hours.
Oxymetazoline (nasal) Special situation	Symptomatic congestion relief, short-term only	2-3 sprays/drops per nostril Q12H PRN, max 2 doses/24h, max 3-5 consecutive days	Rebound congestion beyond 3-5 days; burning, dryness	No trial evidence specifically in rhinosinusitis. Avoid with MAOIs.
Amoxicillin Preferred	1st-line antibiotic when indicated	Adults: 500 mg-1g PO TID. Children standard-dose: 40 mg/kg/day TID; high-dose: 90 mg/kg/day BID-TID	Usually well tolerated; nausea, diarrhea, rash	First choice in adults and children — best amoxicillin activity of any oral beta-lactam against S. pneumoniae, lower resistance-inducing potential than macrolides, inexpensive.
Doxycycline Alternative	True penicillin allergy (type I or non-severe type IV)	Adults: 200 mg PO x1 then 100 mg BID. Children: 4 mg/kg/day divided BID, max 200 mg/day	Nausea, photosensitivity, rash	Excellent activity including beta-lactamase-producing organisms; can be given regardless of age for short courses (≤21 days). Avoid in pregnancy.
Amoxicillin/clavulanate Alternative	1st-line failure, or severe presentation/immunocompromise	Adults: 875 mg PO BID. Children: 45 mg/kg/day (amoxicillin component) BID-TID ± additional amoxicillin — see Drug Tables	More diarrhea than amoxicillin alone	Agent of choice after 1st-line failure — covers beta-lactamase-producing H. influenzae/M. catarrhalis.

Special Populations

Pregnancy

Pregnancy rhinitis (hormone-driven congestion mimicking rhinosinusitis) usually resolves within 2 weeks postpartum and should be distinguished from true bacterial rhinosinusitis, which is roughly 6-fold more common in pregnancy and often lacks classic symptoms. Nonpharmacologic measures (saline irrigation) first; acetaminophen for pain/fever; NSAIDs are an alternative but avoid in the second half of pregnancy (ductus arteriosus closure risk in the third trimester, oligohydramnios risk ≥20 weeks). No evidence supports decongestants for rhinosinusitis symptom relief in pregnancy; if used, topical is preferred over oral, minimally (e.g., only at bedtime) for no more than 3-5 days, preferably after the first trimester — avoid oral decongestants in the first trimester (possible gastroschisis risk). Amoxicillin is first-line for confirmed bacterial disease; amoxicillin/clavulanate is safe after amoxicillin failure; cefuroxime for type I/nonsevere type IV penicillin allergy; azithromycin if unable to take any beta-lactam. Avoid fluoroquinolones (safer alternatives usually available), doxycycline (fetal tooth discoloration), clarithromycin (miscarriage risk), and sulfamethoxazole/trimethoprim (neural tube defect risk), particularly in the first trimester.

Breastfeeding

Saline irrigation first-line. Acetaminophen or ibuprofen for pain/fever. Topical decongestants (oxymetazoline, xylometazoline, phenylephrine) considered safe for ≤3-5 days; use oral decongestants cautiously (reduced milk production reported) and only short-acting forms taken right after a feed if needed; watch the infant for irritability, nervousness, insomnia, or excitation. Intranasal corticosteroids are considered safe given minimal absorption. Amoxicillin and amoxicillin/clavulanate are compatible with breastfeeding; cefuroxime or a macrolide are options if amoxicillin cannot be used; use caution with doxycycline, levofloxacin, and moxifloxacin, avoiding repeated/prolonged exposure. Watch the breastfed infant for thrush, rash, or diarrhea with any antibiotic.

Recent antibiotic use

Antibiotic exposure within the prior 3 months is a risk factor for resistant S. pneumoniae, especially to macrolides and fluoroquinolones — choose a different antibiotic class if this applies.

Monitoring & Follow-Up

Inform patients that improvement, not full resolution, within 7 days is the marker of treatment efficacy — complete symptom resolution can take up to 21 days. Routine follow-up after completing therapy is not needed in an asymptomatic patient. If the patient deteriorates at any point, reassess for a complication (see Red Flags), an alternative diagnosis, or nonadherence rather than simply extending or escalating therapy.

Treatment Failure / Next Step

Reassess the diagnosis — confirm this is still acute bacterial rhinosinusitis, not a complication, dental source, or primary headache syndrome.
Treatment failure is defined as no improvement after 3-5 days of an appropriate antibiotic (2025 AAO-HNSF), or up to 7 days by older criteria — reassess promptly rather than waiting the full week if the patient is worsening.
If failed on amoxicillin (standard- or high-dose): switch to amoxicillin/clavulanate (with additional amoxicillin if the prior failure was on high-dose amoxicillin, amoxicillin/clavulanate alone is adequate).
If penicillin-allergic and failed doxycycline/cefuroxime: consider clindamycin + cefixime (pediatric) or levofloxacin/moxifloxacin (adult, when unable to take any beta-lactam).
Consider resistant organisms specifically — penicillin-resistant S. pneumoniae and beta-lactamase-producing H. influenzae — when selecting the next agent.
Refer to ENT for failure of second-line therapy, ≥4 episodes/year, anatomic anomalies, or any complication.

Common Errors to Avoid

Prescribing an antibiotic based on nasal discharge colour — this reflects neutrophils, not bacterial cause, and does not predict antibiotic benefit.
Ordering a sinus x-ray or CT to "confirm" bacterial rhinosinusitis — imaging cannot distinguish viral from bacterial disease and is not recommended for uncomplicated cases.
Framing antibiotics as necessary to prevent complications — complication rates are similar with or without antibiotic treatment.^[4]
Reaching for amoxicillin/clavulanate as routine first-line therapy — amoxicillin alone is preferred by Canadian/AAO-HNSF experts given equivalent efficacy, lower cost, and fewer adverse effects, despite IDSA's differing recommendation.
Using a macrolide (azithromycin, clarithromycin) as a routine alternative — inferior coverage of H. influenzae and S. pneumoniae, and higher resistance rates than amoxicillin.
Continuing antibiotic therapy for a full extra week after symptoms resolve — short-course optimal-dose therapy (5-7 days in adults) is equally effective and causes fewer adverse effects.
Labelling a nonspecific reaction as a penicillin "allergy" without clarifying true IgE-mediated status — this pushes patients toward less effective alternatives unnecessarily.
Recommending an oral or topical decongestant, or systemic corticosteroid, based on an assumption of efficacy — none has RCT evidence of benefit in acute rhinosinusitis, and each carries its own real risks (rebound congestion, systemic decongestant effects, corticosteroid harms).

Clinical Decision Algorithm

Assessment and management of acute rhinosinusitis

Patient with symptoms ≤4 weeks: facial pain/pressure, nasal obstruction, purulent discharge, and/or smell disturbance (PODS)

Screen for red flags: altered mental status, periorbital/conjunctival edema, visual changes, ophthalmoplegia, severe headache, neck stiffness, frontal swelling, systemically unwell

Any red flag present

Urgent evaluation for orbital/intracranial complication — imaging, ENT/ophthalmology, likely antibiotics

No red flags — assess time course

Symptoms under 10 days and improving, or classic viral URTI pattern

under 10 days, improving — likely viral

Symptom management only: saline irrigation, analgesics/antipyretics, comfort measures. No antibiotic.

>10 days without improvement, or double sickening — meets ABRS criteria

Assess severity: ≥3 days of fever ≥39°C + purulent discharge/facial pain, or immunocompromised?

Severe or immunocompromised

Start antibiotic now — amoxicillin (± clavulanate/additional amoxicillin if severe); see Drug Tables for allergy/failure pathways

Mild-moderate, quality of life significantly affected, patient prefers treatment

Start antibiotic now — amoxicillin first-line, 5-7 days (adults) or 10 days (children)

Mild-moderate, patient open to antibiotic-sparing approach

Offer: high-dose intranasal corticosteroid trial (reassess 72h) OR watchful waiting up to 7 days with guaranteed reassessment

No improvement after 3-5 days of antibiotic, or worsening at any time: reassess diagnosis, exclude complication, switch antibiotic class if ABRS confirmed

Drug Tables

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Duration: adults, 5-7 days when first-line therapy is used; children, 10 days (data on shorter pediatric courses are lacking). If first-line therapy fails, treat the new agent for 5-10 days (adults) or 10 days (children).

Analgesics/antipyretics

Drug	Dosage	Adverse effects	Drug interactions	Comments
Acetaminophen	Adults: 325-650 mg PO/PR Q4-6H PRN, maximum 4000 mg/day Children: 10-15 mg/kg PO Q4-6H PRN (or 15-20 mg/kg PR), maximum 75 mg/kg/day	Uncommon at recommended dose; hepatotoxicity, nephropathy with chronic use/overdose	Increased hepatotoxicity risk with alcohol/isoniazid. May increase INR with warfarin if ≥2g/day used for ≥3 consecutive days.	Use with caution in liver dysfunction. Check labels of combination products to avoid inadvertent double-dosing.
Ibuprofen	Children under 6mo: 5 mg/kg PO Q8H PRN, maximum 40 mg/kg/day Children ≥6mo: 5-10 mg/kg PO Q6-8H PRN, maximum 40 mg/kg/day Adults, self-care: 200-400 mg PO Q4-6H PRN, maximum 1200 mg/day Adults, supervised: Maximum 2400 mg/day	GI intolerance/bleeding, allergic reactions, tinnitus, nephropathy, fluid retention	Increased bleeding risk with anticoagulants/SSRIs/alcohol. Reduces antihypertensive effect of ACE inhibitors/beta-blockers/diuretics. Increases cyclosporine/methotrexate/lithium levels.	Avoid if dehydrated. No renal dose adjustment but avoid in renal dysfunction.
Naproxen sodium	Adults: 220-550 mg PO Q8-12H PRN, maximum 1375 mg/day (440 mg/day for nonprescription use)	GI intolerance/bleeding, allergic reactions, tinnitus, nephropathy, fluid retention	Same as ibuprofen	Not recommended under 12 years of age.

Intranasal corticosteroids

Modest antibiotic-sparing benefit only (roughly 7 additional patients per 100 with marked improvement over placebo); high-dose regimens are needed, since low doses are no better than placebo. Maximal effect takes 7-14 days — not for immediate relief.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Budesonide	Suspension, ≥6y: 2 sprays/nostril daily, or 1 spray/nostril BID Powder, ≥6y: 2 applications/nostril AM, or 1/nostril BID; max 400 mcg/day	Nasal burning/stinging, nosebleeds	None significant at intranasal doses	Aim spray away from septum. Priming needed; re-prime if unused ≥14 days.
Fluticasone propionate	≥12y: 2 sprays/nostril BID; max 400 mcg/day 4-11y: 1-2 sprays/nostril daily; max 200 mcg/day	Nasal burning/stinging, nosebleeds	None significant	Priming needed; re-prime if unused ≥7 days.
Mometasone	≥12y: 2 sprays/nostril daily 3-11y: 1 spray/nostril daily	Nasal burning/stinging, nosebleeds	None significant	Priming needed; re-prime if unused ≥14 days. High-dose antibiotic-sparing regimen ~400 mcg/day.

Nasal decongestants

No RCT evidence of efficacy specifically in acute rhinosinusitis. Limit topical use to 3-5 days — longer use causes rhinitis medicamentosa (rebound congestion). Efficacy/safety not well studied under 12 years; avoid oral decongestants under 6 years per Health Canada advisory.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Oxymetazoline	≥6y, 0.05%: 2-3 sprays/drops per nostril Q12H PRN, max 2 doses/24h	Transient burning/stinging/dryness; rebound congestion beyond 3-5 days	Avoid with MAOIs (risk persists 2 weeks after stopping a nonselective MAOI)	Caution in hypertension, diabetes, cardiovascular disease, prostatic hyperplasia, hyperthyroidism.
Phenylephrine (nasal)	≥6y, 0.25-0.5%: 2-3 sprays/drops per nostril Q4H PRN, max 6 doses/24h	Transient burning/stinging/dryness; rebound congestion beyond 3-5 days	Avoid with MAOIs	Caution in hypertension, diabetes, cardiovascular disease, prostatic hyperplasia, hyperthyroidism.
Xylometazoline	≥6y, 0.05-0.1%: 1-2 sprays or 2-3 drops per nostril Q8-10H PRN, max 3 doses/24h	Transient burning/stinging/dryness; rebound congestion beyond 3-5 days	Avoid with MAOIs	Caution in hypertension, diabetes, cardiovascular disease, prostatic hyperplasia, hyperthyroidism.

Penicillins

First-line antibiotic class when treatment is indicated.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Amoxicillin	Adults: 500 mg-1 g PO TID Children, standard-dose: 40 mg/kg/day divided TID, maximum 1500 mg/day Children, high-dose: 90 mg/kg/day divided BID-TID, maximum 2-3 g/day	Usually well tolerated; nausea, vomiting, diarrhea, hypersensitivity	May increase methotrexate levels, decrease mycophenolate active metabolite levels; tetracyclines may reduce penicillin efficacy	First-line for bacterial rhinosinusitis. High-dose in children at high resistance risk (age under 2y, recent antibiotic under 3mo, daycare attendance).
Amoxicillin/clavulanate	Adults: 875 mg PO BID Children: 45 mg/kg/day (amoxicillin component, 7:1 ratio) divided BID-TID, ± additional amoxicillin 45 mg/kg/day divided BID-TID to increase total amoxicillin dose while limiting diarrhea	Nausea, vomiting, hypersensitivity; diarrhea more common than amoxicillin alone	Same as amoxicillin	Use after first-line amoxicillin failure. If failed high-dose amoxicillin, amoxicillin/clavulanate alone (without extra amoxicillin) is adequate.

Tetracyclines

Preferred alternative for true penicillin allergy — excellent activity against rhinosinusitis pathogens, less resistance than macrolides, can be used regardless of age for short courses.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Doxycycline	Adults: 200 mg PO x1 dose, then 100 mg PO BID Children: 4 mg/kg/day divided BID, maximum 200 mg/day	Nausea, vomiting, diarrhea, rash, photosensitivity	Increases warfarin effect and digoxin levels. Aluminum/bismuth/iron/magnesium reduce absorption. Alcohol/carbamazepine/phenytoin/phenobarbital reduce doxycycline levels.	Not associated with increasing penicillin resistance in S. pneumoniae, unlike macrolides. Avoid in pregnancy.

Cephalosporins

Drug	Dosage	Adverse effects	Drug interactions	Comments
Cefuroxime	Adults: 500 mg PO BID-TID Children: 20 mg/kg/day divided BID, maximum 500 mg/day	Nausea, vomiting, diarrhea, hypersensitivity (negligible cross-reactivity with penicillins)	May increase nephrotoxicity of aminoglycosides; possible increased INR with warfarin	Use for pediatric or select pregnant patients with IgE-mediated or nonsevere type IV penicillin allergy.
Cefixime	Children: 8 mg/kg/day divided BID, maximum 400 mg/day	Nausea, vomiting, diarrhea, hypersensitivity (negligible cross-reactivity)	May increase aminoglycoside nephrotoxicity; possible increased INR with warfarin	Pediatric only — use only in combination with clindamycin for penicillin-allergic children who have failed first-line therapy.
Ceftriaxone	Adults: 1-2 g IV once daily Children: 50-75 mg/kg IV once daily, maximum 1000 mg/day	Nausea, vomiting, diarrhea, hypersensitivity (negligible cross-reactivity)	Enhances alcohol and aminoglycoside toxicity; forms an insoluble precipitate with IV calcium — do not co-administer	Reserve for severe presentation.

Lincosamides

Drug	Dosage	Adverse effects	Drug interactions	Comments
Clindamycin	Children: 20-30 mg/kg/day divided TID-QID, maximum 1200-1800 mg/day	Diarrhea (common, including C. difficile-associated diarrhea)	Kaolin reduces clindamycin absorption; clindamycin reduces erythromycin absorption	Pediatric only — use only in combination with cefixime for penicillin-allergic children who have failed first-line therapy. No activity against H. influenzae or M. catarrhalis.

Macrolides

Inferior coverage of H. influenzae and S. pneumoniae versus amoxicillin, and higher resistance rates — not routine alternatives. Reserve for patients unable to take a beta-lactam, particularly in pregnancy/breastfeeding.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Azithromycin	Adults: 500 mg PO once daily x 3 days	GI upset, nausea, vomiting, diarrhea, rash; rare QT prolongation	Use cautiously with other QT-prolonging drugs; possible increased INR with warfarin	Limit to pregnant/breastfeeding patients unable to take a beta-lactam.
Clarithromycin	Adults, regular-release: 500 mg PO BID Adults, extended-release: 1000 mg PO once daily	GI upset, nausea, vomiting, diarrhea, rash; rare QT prolongation	Potent CYP3A4 inhibitor — increases atorvastatin/carbamazepine/digoxin/lovastatin/simvastatin levels; rifampin reduces clarithromycin levels; possible increased INR with warfarin	Limit to breastfeeding patients unable to take a beta-lactam. Avoid in pregnancy (miscarriage risk).

Fluoroquinolones

Reserved for patients unable to take any beta-lactam, given broad spectrum, resistance potential, C. difficile risk, and persistent/disabling side effects (tendinopathy, peripheral neuropathy, neuropsychiatric effects). Health Canada and the FDA restrict use to patients with no alternative treatment options.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Levofloxacin	Adults: 750 mg PO once daily Children: 10-20 mg/kg/day divided once daily or BID, maximum 750 mg/day	Usually well tolerated; headache, dizziness; QTc prolongation; rare tendinopathy, tendon rupture, peripheral neuropathy, neuropsychiatric effects; rare severe liver injury	Antacids/sucralfate/metal cations/dairy reduce absorption. Avoid with other QT-prolonging drugs. May increase warfarin effect and seizure risk with NSAIDs.	May be justified in children with severe beta-lactam allergy or severe infection when reliable alternatives are limited.
Moxifloxacin	Adults: 400 mg PO once daily	Usually well tolerated; headache, dizziness; QTc prolongation; rare tendinopathy, peripheral neuropathy, neuropsychiatric effects; rare severe liver injury	Antacids/sucralfate/metal cations/dairy reduce absorption. Avoid with other QT-prolonging drugs. May increase warfarin effect and seizure risk with NSAIDs. No interaction with calcium.	Adults only.

References

International consensus statement on allergy and rhinology: rhinosinusitis 2021 — International Forum of Allergy & Rhinology (Orlandi RR, Kingdom TT, Smith TL, et al.). Int Forum Allergy Rhinol 2021;11(3):213-739
Clinical Practice Guideline: Adult Sinusitis Update — Otolaryngology-Head and Neck Surgery, American Academy of Otolaryngology-Head and Neck Surgery Foundation (Payne SC, McKenna M, Buckley J, et al.). Otolaryngol Head Neck Surg 2025;173(2 Suppl)
Antibiotics for acute maxillary sinusitis in adults — Cochrane Database of Systematic Reviews (Lemiengre MB, van Driel ML, Merenstein D, et al.). Cochrane Database Syst Rev 2018;9(9):CD006089
Acute sinusitis in adults — New England Journal of Medicine (Rosenfeld RM). N Engl J Med 2016;375(10):962-970
Canadian clinical practice guidelines for acute and chronic rhinosinusitis — Allergy, Asthma & Clinical Immunology (Desrosiers M, Evans GA, Keith PK, et al.). Allergy Asthma Clin Immunol 2011;7(1):2
Intranasal corticosteroids for acute sinusitis — Cochrane Database of Systematic Reviews (Zalmanovici Trestioreanu A, Yaphe J). Cochrane Database Syst Rev 2013;(12):CD005149

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