How is ivermectin dosed by weight for common parasitic infections in adults and children?
Executive summary
Ivermectin dosing for human parasitic infections is weight-based, most commonly prescribed at about 200 micrograms per kilogram (mcg/kg) as a single oral dose for strongyloidiasis and many scabies regimens, while doses from 150–200 mcg/kg are used for onchocerciasis and higher regimens (up to 400 mcg/kg) are used for lymphatic filariasis or research settings; exact tablet counts derive from 3 mg strengths and clinical weight-tables [1] [2] [3] [4]. Children under 15 kg are generally excluded from standard tablet dosing because safety and efficacy data are limited, and scabies or crusted scabies often require repeated dosing schedules rather than a single pill [1] [5] [6].
1. How clinicians convert milligrams to mcg/kg for routine infections
The routine, evidence-based conversion used in clinical practice is approximately 200 mcg/kg (0.2 mg/kg) for intestinal strongyloidiasis and many scabies protocols, meaning a 70 kg adult would receive roughly 14 mg (about five 3 mg tablets) in one dose; official product labeling and major clinical references frame Stromectol to provide ~200 mcg/kg and include a dosing table to translate body weight into 3 mg tablet counts [4] [1] [7].
2. Infection-specific dosing: strongyloidiasis, onchocerciasis, lymphatic filariasis, scabies
Strongyloidiasis is typically treated with a single 200 mcg/kg oral dose and follow-up stool exams to confirm clearance [2] [4]; onchocerciasis dosing historically ranges 150–200 mcg/kg with repeated community or individual retreatment because ivermectin does not kill adult worms [3] [4]; lymphatic filariasis programs and some studies use higher regimens (up to about 400 mcg/kg) tailored to public-health goals, but higher doses increase certain adverse-event risks and require programmatic safeguards [3] [8]; for ordinary scabies many experts recommend two doses of 200 mcg/kg given 7–14 days apart, while crusted scabies protocols may call for multi-dose schedules (three, five, or seven doses on specified days) to cover the mite lifecycle [6] [9].
3. Pediatric considerations and the 15 kg threshold
Regulatory labeling and many clinical resources state ivermectin tablets are indicated for adults and children weighing 15 kg or more, because trials have been limited below that weight and safety/efficacy data are less definitive for children under 15 kg; nevertheless, some programmatic literature and systematic reviews argue children below 15 kg can be dosed cautiously in high-burden settings, a tension between conservative labeling and pragmatic public‑health practice [1] [2] [3] [5].
4. Practical dosing tables and pill counts used in clinics
Clinics commonly use weight bands with 3 mg tablets—examples compiled from dosing guides recommend 15–25 kg = 3 mg once, 26–44 kg = 6 mg once, 45–64 kg = 9 mg once, 65–84 kg = 12 mg once, and for ≥85 kg revert to a per‑kg calculation such as 0.15–0.2 mg/kg—though exact tables vary slightly by source and indication [7] [10] [4].
5. Safety signals, interactions and population-level caveats
Ivermectin is generally well tolerated when used at recommended antiparasitic doses, but higher or repeated doses raise concerns—ocular adverse events in onchocerciasis, neurotoxicity in rare cases, and severe reactions in persons heavily infected with Loa loa have been documented, so prescribers in endemic areas screen and monitor accordingly [3] [8] [11]. Regulatory labels and public-health guidance stress taking tablets on an empty stomach (labeling specifics) and confirmatory stool or clinical follow-up after treatment [4] [2].
6. Where guidance diverges and why it matters
Differences among product labels, national mass‑drug administration protocols, and academic reviews reflect tradeoffs between strict safety conservatism (excluding <15 kg) and pragmatic needs in endemic regions where meta-analyses suggest acceptable safety at lower weights; readers should note the implicit agendas—regulatory conservatism protects against liability, programmatic literature prioritizes population control of parasites, and review articles may emphasize utility in resource-limited settings [1] [3] [5].