A 32-year-old woman presents with severe pruritus, particularly worse at night, affecting the interdigital spaces, flexural surfaces, and genitalia. Burrows are visible on dermoscopy. She has a 2-week history of symptoms. What is the drug of choice for treatment of scabies in this patient?

Explanation

## First-Line Treatment of Scabies **Key Point:** Permethrin 5% cream is the gold standard and first-line treatment for scabies globally, including in India. ### Why Permethrin? **High-Yield:** Permethrin is a synthetic pyrethroid insecticide with the following advantages: - **Efficacy:** >95% cure rate with 2 applications 1–2 weeks apart - **Safety:** Minimal systemic absorption; safe in infants >2 months and pregnant women (Category B) - **Speed:** Rapid onset of action; pruritus relief within 24–48 hours - **Resistance:** Rare resistance reported globally ### Application Protocol 1. Apply from neck down to entire body (including interdigital spaces, flexural areas, genitalia, and buttocks) 2. Leave on for 8–14 hours (overnight application preferred) 3. Wash off thoroughly 4. Repeat application after 1–2 weeks 5. Treat all close contacts simultaneously ### Comparative Efficacy Table | Agent | Efficacy | Safety in Pregnancy | Resistance | Ease of Use | |-------|----------|-------------------|-----------|-------------| | **Permethrin 5%** | 95–98% | Safe (Cat B) | Rare | Excellent | | Benzyl benzoate 10% | 90–95% | Avoid (Cat C) | Rare | Moderate (irritant) | | Sulfur 5% | 85–90% | Safe | Rare | Poor (messy, odorous) | | Crotamiton 10% | 70–80% | Safe | Emerging | Moderate | **Clinical Pearl:** In patients with contraindications to permethrin (rare allergy to pyrethrins), benzyl benzoate is the next choice, though it causes more skin irritation and is contraindicated in pregnancy. **Mnemonic:** **PERM** = **P**ermethrin is **E**xcellent, **R**are resistance, **M**inimal toxicity. ### Special Populations - **Infants <2 months:** Sulfur 5% ointment (permethrin not studied) - **Pregnant women:** Permethrin 5% (safest option) or sulfur 5% - **Immunocompromised (Norwegian scabies):** Permethrin 5% + oral ivermectin (2 doses, 1–2 weeks apart) [cite:Dermatology Textbook, Scabies Management]