What is the appropriate treatment for scabies involving the penis?

Treatment of Scabies Involving the Penis

Apply permethrin 5% cream to the entire body from the neck down (including the penis and scrotum) for 8-14 hours, then wash off; one application is generally curative. 1, 2

First-Line Treatment Protocol

• Permethrin 5% cream is the recommended first-line therapy for scabies affecting any body site, including genital involvement. 1, 3, 4
• Apply thoroughly to all skin surfaces from the neck down, ensuring coverage of the penis, scrotum, and all genital folds. 2, 5
• Leave on for 8-14 hours (typically overnight), then wash off completely. 1, 2
• The penis and scrotum are common sites for scabies lesions in men, making thorough application to these areas essential. 5, 6, 7

Alternative Oral Therapy

• Oral ivermectin 200 μg/kg is an effective alternative, repeated in 2 weeks. 1, 3, 4
• Must be taken with food to ensure adequate bioavailability and epidermal penetration. 3, 4
• Particularly useful when topical application is impractical or in institutional outbreaks. 1, 5

Critical Management Steps to Prevent Treatment Failure

• Treat all sexual partners and household contacts within the past month simultaneously, even if asymptomatic. 1, 3, 4
  • Failure to treat contacts simultaneously is the most common cause of treatment failure. 8
• Decontaminate all bedding, clothing, and towels by machine washing/drying on hot cycle or isolating from skin contact for 72 hours. 1, 3, 4
• Fumigation of living areas is unnecessary. 1, 3

Expected Post-Treatment Course

• Pruritus and rash may persist for up to 2 weeks after successful treatment due to allergic dermatitis, not treatment failure. 1, 3, 4
• This persistent itching does not indicate the need for immediate retreatment. 2
• Retreatment is only indicated if live mites are observed after 14 days or if symptoms persist beyond 2 weeks. 1, 3, 4, 2
• Use an alternative regimen (switch between permethrin and ivermectin) if retreatment is needed. 1, 4

Treatments to Avoid

• Do not use lindane in children <10 years, pregnant/lactating women, or persons with extensive dermatitis due to neurotoxicity risk (seizures, aplastic anemia). 1, 3, 4
• Lindane should never be applied after bathing, as this increases systemic absorption and toxicity. 1, 8
• Lindane is the least expensive option but has the highest toxicity profile. 1

Special Clinical Scenarios

• For bullous scabies (rare variant that can present with bullae on penile skin), the same permethrin or ivermectin regimen is curative. 9
• If crusted (Norwegian) scabies is suspected (thick crusts, immunocompromised patient), use combination therapy: permethrin daily for 7 days then twice weekly, plus oral ivermectin on days 1,2,8,9, and 15, with specialist consultation. 3, 4

Common Pitfalls

• Inadequate application to genital areas due to patient embarrassment or oversight. 8
• Not applying under fingernails and to all body orifices. 8
• Expecting immediate symptom resolution and retreating prematurely within the first 2 weeks. 1, 2
• Failing to treat asymptomatic sexual partners, leading to reinfection. 1