How does ivermectin dosing differ between scabies, strongyloidiasis, and onchocerciasis?

1. Different parasites, different targets — and different dose plans

Strongyloides stercoralis (strongyloidiasis) is typically treated with a single 200 µg/kg oral dose of ivermectin (0.2 mg/kg) and clinicians may repeat or give suppressive courses in immunocompromised patients; this single-dose convention is cited by MSF and WHO-related reviews and drug monographs ^{[1] [2] [4]}. Onchocerca volvulus (onchocerciasis) is managed with lower single doses — commonly 150 µg/kg — given in mass drug administration or repeated at intervals (often 1–4 times per year in control programs), because ivermectin clears microfilariae but does not reliably kill the adult worms ^{[2] [5]}. Scabies is usually treated with ivermectin at roughly 200 µg/kg per dose but the regimen differs: most guidelines recommend two doses spaced one to two weeks apart for ordinary scabies; crusted scabies requires multiple doses on days 1, 2, 8 and sometimes further doses ^{[3] [1]}.

2. Single dose versus repeat dosing — why schedules diverge

The biological reasons explain the dose patterns: strongyloidiasis infects the intestinal tract where a single systemic dose often suffices to clear larvae, whereas onchocerciasis involves long-lived adult worms in tissues that are not killed by ivermectin; therefore onchocerciasis control relies on repeated community dosing to suppress microfilariae and transmission rather than a one-time “cure” ^{[2] [4]}. Scabies mites on skin and in burrows require re-treatment because ivermectin does not reliably affect eggs; hence the conventional two-dose schedule one week or two weeks apart — and far more aggressive regimens for crusted scabies where mite burden is enormous ^{[3] [6]}.

3. Programmatic dosing vs. individual therapy: public-health nuance

Onchocerciasis dosing in control programs often uses 150 µg/kg administered periodically across entire communities; that public-health schedule is distinct from individualized clinical treatment for other helminths ^[2]. WHO guidance and mass drug administration experiences inform the 150 µg/kg repeating schedules used to reduce transmission — a strategy different from single-dose curative intent for strongyloidiasis ^[2].

4. Practical differences: fasting, food and formulation notes

Sources note practical administration differences: some guidance recommends taking ivermectin on an empty stomach for strongyloidiasis and onchocerciasis because the drug’s lipophilicity affects absorption; by contrast, some dermatology guidance suggests taking doses for scabies with food to improve skin penetration, though recommendations vary across references ^{[7] [5]}. Topical ivermectin formulations exist for dermatologic use, but most dosing guidance cited here refers to oral tablets ^{[3] [5]}.

5. Special situations: immunosuppression, crusted scabies and adverse reactions

Immunocompromised patients with strongyloidiasis may need repeated or suppressive ivermectin therapy and stool monitoring because single doses sometimes fail to clear infection in those populations ^{[5] [4]}. Crusted scabies requires intensified regimens — multiple doses over days and weeks and combined topical therapy — because systemic drug penetration and heavy mite loads demand repeated treatment ^[3]. Onchocerciasis patients can experience Mazzotti reactions (inflammatory response to dying microfilariae) after ivermectin, a safety issue emphasized in clinical monographs ^{[5] [4]}.

6. Where sources agree and where they diverge

Most clinical and programmatic sources converge on these core numbers: 200 µg/kg single dose for strongyloidiasis and 150 µg/kg single dose (with repeat community rounds) for onchocerciasis ^{[1] [2]}. For scabies, guidelines commonly use 200 µg/kg with repeat dosing at 1–2 weeks; for crusted scabies they document intensified multi-day schedules ^{[3] [6]}. Minor discrepancies exist in lay or tertiary sites about exact timing (day‑7 vs day‑14 repeats) and about whether to take with food — these reflect differences between dermatology practice notes, drug labels and programmatic guidance ^{[7] [5] [3]}.

7. Limitations and what the sources don’t say

Available sources do not mention a single universally authoritative international standard that harmonizes every timing and food‑timing nuance across all clinical settings; instead guidance is disease- and context-specific and sometimes varies by guideline or program (not found in current reporting). Also, comparative head‑to‑head randomized trials defining “best” scabies interval (7 vs 14 days) or ideal food instructions across indications are not summarized in these excerpts (not found in current reporting).

Bottom line: treat strongyloidiasis with a 200 µg/kg single oral dose (repeat/suppress if immunocompromised), manage onchocerciasis with ~150 µg/kg single doses used in repeated community rounds, and use ~200 µg/kg for scabies with two doses 1–2 weeks apart (escalating to multi‑dose regimens for crusted scabies); consult local guidelines and specialists for immunosuppressed patients and programmatic campaigns ^{[1] [2] [3]}.