How is ivermectin dose calculated by weight for common parasitic infections?
Executive summary
Ivermectin dosing for human parasitic infections is weight-based and generally expressed in micrograms per kilogram (mcg/kg); the usual therapeutic range for common infections is about 150–200 mcg/kg as a single oral dose, with higher or repeated regimens used for specific diseases such as lymphatic filariasis or crusted scabies (150–200 mcg/kg for onchocerciasis and strongyloidiasis; 400 mcg/kg used in some filariasis programs) [1] [2] [3].
1. How the math works: converting mcg/kg into tablets
Dosing begins with the prescribed mcg/kg for the target infection and the patient’s body weight in kilograms; multiply the weight by the mcg/kg dose to get the total micrograms, convert micrograms to milligrams (1,000 mcg = 1 mg), then divide by the tablet strength to determine number of tablets — for example, a 70 kg adult at 200 mcg/kg requires 14,000 mcg (14 mg), which is approximately five 3 mg tablets [4] [5] [3].
2. Common regimens by indication
First-line human indications reported across clinical references and product labeling include strongyloidiasis and onchocerciasis typically treated with single doses in the 150–200 mcg/kg range, while lymphatic filariasis programs sometimes use higher doses such as 400 mcg/kg in mass-treatment regimens; scabies and ectoparasite uses often rely on 200 mcg/kg and may require repeat dosing depending on severity (for crusted scabies multiple doses across days are documented) [1] [2] [6] [7].
3. Practical dosing details and administration
Commercial human tablets are commonly 3 mg (and sometimes 6 mg/12 mg formulations), and regulatory labeling for the widely prescribed brand Stromectol is designed to approximate 200 mcg/kg per dose with guidance to take tablets on an empty stomach with water for many indications, although some dermatology sources advise taking ivermectin with food for scabies to improve absorption — clinicians adjust timing and repetition by indication [3] [7] [8].
4. Safety margins, monitoring and when doses differ
Clinical reviews and product labels emphasize that single-dose regimens are generally sufficient for many intestinal nematode infections, but higher or repeated dosing increases the risk of adverse events (ocular and inflammatory reactions have been observed with higher microfilaricidal exposures), and monitoring such as stool exams for Strongyloides or clinical follow-up for onchocerciasis is advised to confirm eradication or need for retreatment [3] [1] [9].
5. Limits, controversies and misuse
There is substantial consensus in official and clinical sources that ivermectin is approved for certain parasitic infections and not for COVID-19; off-label uses and public confusion have driven inappropriate self-medication and use of veterinary formulations, a public health concern repeatedly noted in reviews and guidance documents — authoritative sources stress prescription-only use and clinician-calculated weight-based dosing to avoid harm [10] [11] [7].
6. Evidence base and programmatic use
Decades of research and mass-drug-administration campaigns underpin the dosing conventions: numerous studies and program protocols use 150–200 mcg/kg as standard and have distributed billions of treatments in control programs, while dose-finding research continues for other roles such as malaria transmission reduction where higher or repeated doses are under study [12] [13] [2].
7. Practical takeaways for clinicians and programs
Clinicians calculate total dose as weight (kg) × prescribed mcg/kg, convert to milligrams, then select the nearest appropriate tablet count (avoiding veterinary products), schedule single or repeat doses per indication, and monitor for efficacy and adverse effects — product labeling and clinical guidance (Stromectol/tablet tables, dermatology cheat sheets, program protocols) provide the specific weight-to-tablet tables and indication-specific variations that clinicians should follow [3] [5] [8].