A 32-year-old woman presents with intense pruritus, worse at night, affecting the interdigital spaces, flexural surfaces of wrists, and lower abdomen. Burrows are visible on dermoscopy. She has been treated with permethrin 5% cream applied once. All of the following are true regarding scabies management EXCEPT:

Explanation

## Scabies Management: Treatment Principles ### Topical Permethrin — Standard First-Line Therapy **Key Point:** Permethrin 5% cream is the gold standard for scabies in immunocompetent individuals and should be applied to the entire body surface below the neck, including interdigital spaces, flexural areas, genitalia, and buttocks. In children <2 years and pregnant women, application to face and scalp may be included under medical supervision. ### Why Repeat Application Is Essential **High-Yield:** Scabies mites lay eggs in burrows within the stratum corneum. A single application kills adult mites and nymphs but does NOT reliably eliminate eggs. Eggs hatch in 3–5 days, and nymphs mature in 4–5 days. Therefore, a **second application 7–14 days later** is standard to catch newly emerged mites before they mature and lay new eggs. ### Household and Contact Treatment **Clinical Pearl:** All household members and close contacts (sexual partners, family members sharing bedding) must be treated simultaneously, regardless of symptoms. Asymptomatic carriers can perpetuate transmission. ### Oral Ivermectin — Selective Use, NOT First-Line for All **Warning:** The statement "oral ivermectin is first-line for all cases" is **incorrect**. Ivermectin is: - **Second-line** for immunocompetent patients (reserved for permethrin failure, intolerance, or contraindication). - **Preferred** for crusted (Norwegian) scabies and immunocompromised patients (e.g., HIV with CD4 <200). - **Not recommended** as monotherapy in immunocompetent patients because it does not reliably kill eggs; two doses 1–2 weeks apart are needed. - **Contraindicated** in pregnancy and children <15 kg. **Mnemonic:** **PERM-FIRST** — Permethrin is first-line in immunocompetent scabies; Ivermectin for exceptional cases (crusted, immunocompromised, or topical failure). ### Summary Table: Scabies Treatment Regimens | Scenario | First-Line | Alternative | Key Notes | | --- | --- | --- | --- | | Immunocompetent adult | Permethrin 5% × 2 (7–14 days apart) | Ivermectin 200 µg/kg × 2 doses | Topical preferred; eggs require second dose | | Crusted scabies | Ivermectin 200 µg/kg × 2 doses (1–2 weeks apart) + topical permethrin | Topical alone insufficient | High parasite load; systemic needed | | HIV CD4 <200 | Ivermectin + permethrin | Permethrin alone (if ivermectin unavailable) | Systemic preferred due to immunosuppression | | Pregnancy | Permethrin 5% (topical only) | Sulfur 5–10% (safe in pregnancy) | Avoid ivermectin (teratogenic) | | Children <2 years | Sulfur 5–10% or permethrin under supervision | Ivermectin (weight-based, off-label) | Face/scalp application acceptable | [cite:Irvine Dermatology 6e Ch 14]