Impetigo and Ecthyma
Clinical Snapshot
Impetigo is a superficial bacterial skin infection caused mainly by S. aureus and S. pyogenes.[1] Nonbullous disease produces characteristic honey-coloured crusting; bullous impetigo is toxin-mediated and produces fragile, fluid-filled bullae. Ecthyma is a deeper, ulcerative form that extends into the dermis and generally requires systemic treatment. Localized nonbullous disease is treated topically; widespread, bullous, or ecthymatous disease needs systemic treatment.
Recognize the Condition
The impetigo/ecthyma spectrum
Nonbullous (most common)
- Papules/vesicles/pustules rupture and leave adherent honey-coloured crust.
- Often on the face or exposed extremities.
- May arise on previously healthy skin (primary) or over eczema/abrasions (secondary impetiginization).
Bullous
- Flaccid, fluid-filled bullae that rupture easily, toxin-mediated by S. aureus.
- Leaves a thin brown crust or superficial erosion; commonly on the trunk.
Ecthyma
- Deeper, punched-out ulcer under an adherent crust, extending into the dermis.
- More commonly associated with S. pyogenes than S. aureus.
- Always requires systemic (oral or IV) treatment.
Risk Factors
- Broken skin, abrasions, insect bites, or eczema.
- Close-contact environments and shared personal items.
- Warm/humid conditions.
- S. aureus carriage and recurrent disease.
- Poor hygiene or inability to keep lesions covered.
Red Flags & Refer
Refer for any of the following:
- Extensive bullous disease.
- Fever or systemic toxicity.
- Rapidly spreading cellulitis.
- Deep ulceration.
- Periorbital involvement.
- Immunocompromise.
- Treatment failure.
- Any concern for staphylococcal scalded skin syndrome (widespread painful erythema with skin sloughing, typically in infants/young children).
Assessment & Diagnosis
Diagnosis is usually clinical. Assess lesion number, distribution, presence of bullae, depth, surrounding cellulitis, fever, and underlying eczema. Culture exudate when disease is recurrent, extensive, treatment-resistant, associated with MRSA risk, or when the diagnosis is uncertain.
Differential diagnosis
Herpes simplex / herpes zoster
Clustered painful vesicles, often dermatomal (zoster) or recurrent at the same site (HSV) — do not treat as impetigo without considering this.
Infected eczema
Underlying barrier disease with secondary crusting — treat both the eczema and the infection.
Contact dermatitis
Itch and an exposure pattern dominate; no honey-coloured crust.
Insect bites / fungal infection
Consider when distribution or history doesn't fit typical impetigo.
Treatment Targets
- Stop new lesion formation and bacterial spread.
- Heal erosions/ulcers and relieve discomfort.
- Prevent secondary cellulitis and household transmission.
- Control underlying skin-barrier disease (eczema) driving secondary impetiginization.
Choose Initial Treatment
Few localized nonbullous lesions
1st line: topical mupirocin or fusidic acid for a short 5-day course.
Multiple lesions, bullous impetigo, ecthyma, systemic symptoms, or topical failure
1st line: oral cephalexin.
Alternative for confirmed/suspected MRSA: doxycycline or trimethoprim-sulfamethoxazole (add streptococcal coverage if that pathogen is not excluded).
Non-Pharmacologic Treatment
- Warm saline or water compresses for 10-15 minutes, several times daily, to soften and remove crusts.
- Cover draining lesions.
- Hand hygiene and laundering of towels, bedding, and clothing.
- Do not share razors, towels, or face cloths.
- Treat active eczema or other barrier disruption concurrently.
Special Populations
Children
Impetigo is common in children; use weight-based systemic dosing only when systemic therapy is indicated. Carefully distinguish bullous impetigo from more extensive toxin-mediated staphylococcal scalded skin syndrome.
Pregnancy / breastfeeding
Topical mupirocin has minimal systemic absorption and is compatible. When oral therapy is required, cephalexin is generally preferred when the organism is susceptible. Avoid infant skin contact with recently medicated topical areas during breastfeeding.
Ontario pharmacist prescribing
Impetigo is within Ontario's minor-ailments prescribing scope. Provincial regulation lists bacitracin, fusidic acid, gramicidin, mupirocin, ozenoxacin, and polymyxin B as eligible topical drugs; clinical selection must still follow evidence, product availability, and the patient's presentation.[2]
Monitoring & Follow-Up
Localized disease should show fewer new lesions and less exudate within 48-72 hours. Reassess lack of improvement, extension beyond the original area, fever, or pain. After a full course, persistent lesions require culture and reconsideration of the diagnosis.
Common Errors to Avoid
- Using topical antibiotics for extensive disease.
- Continuing topical antibiotics beyond a short defined course.
- Missing ecthyma, which always requires systemic therapy.
- Treating herpes zoster or herpes simplex as impetigo.
- Ignoring infected eczema underlying the impetigo.
Clinical Decision Algorithm
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.
Topical agents (localized nonbullous disease)
Ontario pharmacist-prescribable drugs for impetigo under the province's minor-ailments program.
| Drug | Dosage | Adverse effects | Comments |
|---|---|---|---|
| Mupirocin 2% | Treatment (all ages): Apply BID-TID for 5 days | Local stinging, rare contact dermatitis | Covers MSSA and MRSA. |
| Fusidic acid 2% | Treatment (all ages): Apply BID-TID for 5 days | Rare allergic contact dermatitis | Similar efficacy to mupirocin. |
Systemic agents (extensive / bullous / ecthyma)
| Drug | Dosage | Adverse effects | Comments |
|---|---|---|---|
| Cephalexin | Adults: 250-500 mg PO QID for 5-7 days Children: 25-50 mg/kg/day divided Q6H PO for 5-7 days (max 1000 mg/day) | GI upset, hypersensitivity | 1st-line oral agent. |
| Cefadroxil | Adults: 500 mg PO daily-BID Children: 20 mg/kg PO once daily (max 500 mg/day) | GI upset, hypersensitivity | Alternative oral beta-lactam. |
| Cloxacillin | Adults: 250-500 mg PO QID Children: 12.5-25 mg/kg PO QID (max 500 mg/dose) | GI upset, hypersensitivity | Less convenient due to QID dosing. |
| Clindamycin | Adults: 300-450 mg PO TID Children over 1 month: 25-40 mg/kg/day divided Q8H PO (max 450 mg/dose) | Diarrhea, C. difficile infection | Severe beta-lactam allergy / culture-directed MRSA option. |
| Doxycycline | Adults: 100 mg PO BID Children over 8 years: 2-4 mg/kg/day divided Q8-12H PO (max 100 mg/dose) | Photosensitivity, esophagitis | MRSA-directed; avoid in pregnancy and children under 8. |
| Sulfamethoxazole/Trimethoprim | Adults: 1-2 DS tablets PO BID Infants (2 months+), children, adolescents: 8-12 mg/kg/day (TMP component) divided Q12H PO | Rash, hyperkalemia, cytopenias | MRSA-directed; add streptococcal coverage if needed. |
References
- Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America — Clinical Infectious Diseases (Stevens DL, Bisno AL, Chambers HF, et al.). Clin Infect Dis 2014;59(2):e10-e52
- Minor Ailments: Pharmacist Prescribing — Ontario College of Pharmacists. Ontario Regulation 202/94, Schedule 4
- Impetigo: diagnosis and treatment — American Family Physician (Hartman-Adams H, Banvard C, Juckett G). Am Fam Physician 2014;90(4):229-235
- Interventions for impetigo — Cochrane Database of Systematic Reviews (Koning S, van der Sande R, Verhagen AP, et al.). Cochrane Database Syst Rev 2012;1:CD003261
- Staphylococcus aureus decolonization for recurrent skin and soft tissue infections in children — Canadian Family Physician (Smith CH, Goldman RD). Can Fam Physician 2012;58(12):1350-1352
Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.