A 4-year-old boy presents with fluid-filled blisters on the neck and axillae that rupture easily, leaving a thin, varnish-like crust. Gram stain confirms Gram-positive cocci. What is the drug of choice for bullous impetigo?

Question

Accepted Answer

A. Cloxacillin. ## Drug of Choice for Bullous Impetigo

**Key Point:** Bullous impetigo (~30% of impetigo cases) is caused **exclusively** by *Staphylococcus aureus* (phage group II strains producing exfoliative toxins). Despite the different clinical presentation, the antibiotic choice remains **antistaphylococcal penicillin** — cloxacillin is first-line.

### Pathophysiology of Bullous Impetigo

Bullous impetigo results from toxin-mediated intraepidermal acantholysis:
- **Exfoliative toxins** (ETA/ETB) produced by *S. aureus* disrupt **desmoglein-1** (superficial epidermis)
- Creates **subcorneal blistering** (unlike pemphigus vulgaris, which is autoimmune)
- Blisters rupture easily → thin, varnish-like crust (characteristic finding)

### Treatment Comparison: Bullous vs. Non-Bullous

| Feature | Non-Bullous | Bullous |
| --- | --- | --- |
| **Causative organism** | S. aureus + S. pyogenes | S. aureus only |
| **First-line drug** | Cloxacillin | Cloxacillin |
| **Route** | Oral (localized) or IV | Oral (if mild) or IV (if severe) |
| **Duration** | 7–10 days | 7–10 days |
| **Systemic toxicity risk** | Low | Moderate (risk of staphylococcal scalded skin syndrome in infants) |

**High-Yield:** The **drug choice is identical** for both bullous and non-bullous impetigo because both are staphylococcal infections. The difference lies in **severity assessment** — bullous impetigo may warrant IV therapy if extensive or in infants <5 years.

### Why Cloxacillin, Not Amoxicillin-Clavulanate?

**Clinical Pearl:** While amoxicillin-clavulanate covers β-lactamase-producing S. aureus, cloxacillin is **preferred** because:
1. **Inherent resistance** to β-lactamase (no need for clavulanate)
2. **Better tissue penetration** into skin and soft tissue
3. **Lower cost** in India
4. **Established efficacy** in bullous impetigo trials

Amoxicillin-clavulanate is a reasonable alternative but is not first-line.

**Warning:** Do NOT use erythromycin or TMP-SMX as monotherapy — resistance is high and they lack the superior skin penetration of β-lactamase-resistant penicillins.

**Mnemonic:** **BISS** = **B**-lactamase-resistant penicillin for **I**mpetigo (both **S**ub-types) and **S**taphylococcal skin infections.

[cite:Fitzpatrick's Dermatology 9e Ch 190; Park 26e Ch 6]

Answer

B. Erythromycin

Answer

C. Trimethoprim-sulfamethoxazole

Answer

D. Amoxicillin-clavulanate

A 4-year-old boy presents with fluid-filled blisters on the neck and axillae that rupture easily, leaving a thin, varnish-like crust. Gram stain confirms Gram-positive cocci. What is the drug of choice for bullous impetigo?

Explanation

Drug of Choice for Bullous Impetigo

Pathophysiology of Bullous Impetigo

Treatment Comparison: Bullous vs. Non-Bullous

Why Cloxacillin, Not Amoxicillin-Clavulanate?

Practice similar questions

Join our NEET PG community

Feature	Non-Bullous	Bullous
Causative organism	S. aureus + S. pyogenes	S. aureus only
First-line drug	Cloxacillin	Cloxacillin
Route	Oral (localized) or IV	Oral (if mild) or IV (if severe)
Duration	7–10 days	7–10 days
Systemic toxicity risk	Low	Moderate (risk of staphylococcal scalded skin syndrome in infants)