What are the recommended ivermectin dosing schedules for crusted scabies in immunocompromised patients?
Executive summary
Crusted (Norwegian) scabies is managed with oral ivermectin at a standard per‑dose of 200 micrograms (µg) per kilogram, but immunocompromised patients typically require multiple, repeated doses rather than a single treatment [1] [2]. Experts and guidelines propose several multi‑dose schedules for crusted scabies — commonly three, five, or seven doses on specified days — and these regimens are recommended to be given together with topical scabicides because thick crusts may impede systemic drug penetration [2] [3] [4].
1. What “200 µg/kg” means and why dosing matters
Ivermectin dosing for scabies is conventionally expressed as 200 µg per kg of bodyweight — roughly 0.2 mg/kg — a dose repeatedly used in trials and guidelines as the baseline for systemic therapy [1] [5]. That single dose cures many uncomplicated cases and even some immunocompromised patients, but crusted scabies involves hyperinfestation and higher parasite burden, so repeated dosing is required more often than in classic scabies [6] [7].
2. Common multi‑dose regimens recommended for crusted scabies
Public health guidance and specialty guidelines list several multi‑dose ivermectin regimens for crusted scabies: a three‑dose schedule (approximately days 1, 2, and 8), a five‑dose schedule (days 1, 2, 8, 9, and 15), and an extended seven‑dose schedule (days 1, 2, 8, 9, 15, 22, and 29), all using 200 µg/kg per dose; choice among them depends on severity and expert judgment [2] [8]. Other statements in the literature recommend two doses 7–14 days apart for less severe disease, but for crusted scabies many authorities explicitly propose the more intensive multi‑dose approaches above [5] [8].
3. Evidence base: trials, case series and guideline synthesis
The evidence is a mix of randomized trials, observational studies and case reports: early controlled work showed many HIV‑infected patients were cured with a single 200 µg/kg dose though some required a second dose two weeks later [6], while open‑label series and case reports of crusted scabies document that two, three or more doses given days to weeks apart were needed for cure in many patients [7] [9] [10]. Systematic reviews and guideline panels synthesize these heterogeneous studies and therefore endorse varied multi‑dose regimens rather than a single standardized protocol, noting that patients with crusted scabies were often excluded from primary RCTs and that direct comparative evidence is limited [8].
4. Concomitant topical therapy, adjuncts and clinical practice caveats
Guidelines and case reports uniformly recommend combining oral ivermectin with topical scabicides (permethrin 5% or benzyl benzoate) and keratolytic care for crusted scabies because crusts may prevent adequate topical or systemic penetration; experts differ on the exact frequency of topical application, and there is no universal consensus on how many ivermectin doses definitively guarantee cure [3] [4] [2]. Published regimens range from daily dosing for several days in case reports to the structured repeated‑days schedules in guidelines, and recurrent infestations after treatment have been reported, prompting some clinicians to extend dosing or repeat courses [11] [7].
5. Special populations, safety and practical points
Regimens described in the literature include use in infants, children and immunocompromised adults, but safety in children under 15 kg and in pregnancy remains an area of caution; some case reports used weekly 200 µg/kg dosing for several weeks in infants off‑label whereas guideline recommendations focus on weight thresholds and specialist oversight [12] [2]. Drug interactions and hepatic metabolism considerations are noted in dosing resources, and public health guidance emphasizes treating contacts, environmental control and close follow‑up because reinfestation is common and may mimic treatment failure [5] [8] [2].
Conclusion: recommended practical schedule
For immunocompromised patients with crusted scabies, the authoritative practical options are ivermectin 200 µg/kg per dose given as either a three‑dose course (days 1, 2, 8), a five‑dose course (days 1, 2, 8, 9, 15) or an extended seven‑dose course (adding days 22 and 29) — always administered with topical scabicide and individualized based on clinical severity and response [2] [8] [4]. The precise number of doses should be guided by specialist dermatology or infectious‑disease advice, repeat evaluation, and attention to contacts and environmental decontamination because the literature shows variability in response and a risk of recurrence [7] [8].