Scabies - Prescription Guide

Causative Agent

First-Line Treatment

Permethrin 5% Cream (Drug of Choice)

Permethrin 5% cream - 30 g tube Apply to entire body from neck down at bedtime. Wash off after 8-14 hours. Repeat after 7-14 days.

Second-Line / Alternative: Oral Ivermectin

Tab. Ivermectin 12 mg (200 mcg/kg) Take orally on an empty stomach. Repeat after 7-14 days.

Crusted (Norwegian) Scabies - Special Protocol

• Combined regimen (mandatory): Permethrin 5% cream (daily for 7 days, then twice weekly until cured) + Oral Ivermectin (200 mcg/kg on days 1, 2, 8, 9, 15 - i.e., multiple doses)
• Add keratolytic agents (e.g., salicylic acid 6%) to break down thick crusts before applying permethrin

Symptomatic Relief (Adjunct)

Note: Pruritus may persist 2-4 weeks after successful treatment - this is a hypersensitivity reaction to dead mites/eggs and does NOT indicate treatment failure.

Topical Alternatives (if Permethrin Unavailable)

• Benzyl benzoate 25% lotion - apply overnight, repeat in 24 hours (irritant; dilute to 12.5% for children)
• Sulfur 6-10% in petrolatum - apply for 3 consecutive nights (safe in pregnancy, cheap)
• Crotamiton 10% cream - apply for 2 consecutive nights (less effective)

Essential Non-Drug Measures

1. Treat ALL household contacts simultaneously, even if asymptomatic - failure to do so causes recurrence
2. Wash all clothing, bed linens, and towels in hot water (>50°C)
3. Items that can't be washed: seal in a plastic bag for 72 hours (mites die without a host in ~24-72 hrs) or dry clean
4. Sexual partners should be treated if transmission was sexual

Special Populations

Sources

• Harrison's Principles of Internal Medicine 22E (2025), Scabies section
• Textbook of Family Medicine 9e, Key Treatment (SOR: A evidence)
• Rosen's Emergency Medicine, Scabies chapter
• A 2026 meta-analysis (PMID 42098632) confirms ivermectin and permethrin have comparable effectiveness; a 2024 systematic review (PMID 37625798) specifically addresses treatment failure rates

Disclaimer: This is educational clinical information. Prescriptions must be individualized based on patient weight, age, pregnancy status, comorbidities, and local drug availability. Always follow local/national treatment guidelines.

Recent Clinical Guidelines & Evidence on Scabies Treatment Resistance

The Core Problem: Rising Failure Rates

Key conclusion: Overall treatment failure is increasing by 0.27% per year, with permethrin failing fastest.

Resistance Mechanisms (2024 Review, PMID 39336998)

• Voltage-gated sodium channel (VGSC) mutations in Sarcoptes scabiei - the same "knock-down resistance" (kdr) mutations seen with permethrin resistance in head lice and other insects
• Glutathione S-transferase (GST) overexpression - enhanced detoxification of permethrin by mites
• Ivermectin resistance: Clinical evidence of widespread resistance is currently lacking - some lab tolerance has been reported, and anecdotal resistance in crusted scabies exists, but it is not yet confirmed as a major clinical problem
• Benzyl benzoate resistance: Also unconfirmed at this time

What Current Guidelines Recommend for Resistant Cases

HSE (Ireland) Guideline - Reviewed February 2025

1. First step: Before labelling as resistant, verify strict protocol adherence - correct application technique, all household contacts treated simultaneously, and environmental decontamination done
2. Second step: Seek Dermatology or Microbiology advice
3. For confirmed resistant cases: Oral ivermectin (200 mcg/kg, two doses one week apart - Day 1 and Day 8)

UKHSA (UK) Guidelines - 2025

International Consensus Direction (2025 Updated Review, PMID 40754226)

• First-line: topical permethrin, benzyl benzoate, OR oral ivermectin (per international guidelines)
• Emerging resistance is driving research into moxidectin and combination regimens

Practical Algorithm for Suspected Treatment Failure

Step 1: Rule out pseudo-resistance
  - Was permethrin applied to the ENTIRE body (neck to toes)?
  - Were ALL household contacts treated on the SAME day?
  - Was clothing/bedding washed in hot water?
  - Was the second dose given at 1-2 weeks?
  - Is the itch merely post-treatment hypersensitivity (can persist 4+ weeks)?

Step 2: If genuine failure after 2 full courses →
  Switch to Oral Ivermectin 200 mcg/kg × 2 doses (Day 1 + Day 8)
  Refer to Dermatology/Infectious Disease

Step 3: Crusted scabies or refractory disease →
  Combination: Permethrin 5% (daily × 7 days, then twice weekly) +
  Oral Ivermectin (Days 1, 2, 8, 9, 15 - multiple doses)
  + Keratolytics (e.g., salicylic acid) to enable penetration

Step 4: Research/experimental (no guideline approval yet) →
  Moxidectin | Topical ivermectin 1% lotion | Spinosad

Emerging & Future Therapies Being Investigated

Bottom Line for Clinical Practice

1. Permethrin resistance is real and rising - 0.58%/year increase in failure rate, driven by VGSC mutations and GST overactivity
2. Always give two doses of ivermectin, not one - failure drops from 15.2% to 7.1% (level 1 evidence)
3. Most "treatment failures" are actually compliance failures - verify application technique before switching agents
4. Ivermectin resistance is not yet a significant clinical threat, but permethrin resistance is now well-documented in many regions (especially Western Pacific)
5. Moxidectin is the most promising pipeline drug for permethrin/ivermectin-resistant cases
6. Combination therapy (permethrin + ivermectin) outperforms either drug alone and should be considered for difficult cases