How do dosing tables translate ivermectin mcg/kg into whole tablets for common weight bands?
Executive summary
Dosing tables convert a weight-based microgram-per-kilogram (mcg/kg) ivermectin prescription into whole 3 mg tablets by multiplying patient weight (kg) by the target mcg/kg dose to get total micrograms, then dividing by 3,000 mcg (3 mg) and rounding to a practical whole-tablet amount shown in weight bands (e.g., 15–24 kg = 1 tablet) [1] [2]. Standard clinical targets commonly used are roughly 150–200 mcg/kg for parasitic indications, with some guidance using 150 mcg/kg for onchocerciasis and 200 mcg/kg for strongyloidiasis; tables reflect those targets and practical rounding to whole tablets [2] [3] [4].
1. How the math behind a dosing table actually works
A dosing table is simply an applied arithmetic shortcut: convert body weight in kilograms into micrograms by multiplying kg × prescribed mcg/kg, then divide by tablet strength (3,000 mcg for a 3 mg tablet) to get the number of tablets — the table groups nearby weights into bands and shows the nearest whole‑tablet dose so clinicians can avoid fractional pills [1] [2].
2. Which mcg/kg targets are being translated into tablets
Regulatory and clinical sources commonly endorse different target microgram/kg figures depending on indication — for strongyloidiasis ~200 mcg/kg, for onchocerciasis ~150 mcg/kg, and many dermatology uses or practical guides sit in a 150–250 mcg/kg range — and tables are built to match the selected target [2] [3] [4] [5].
3. Typical weight bands and the resulting whole‑tablet recommendations
Published tables used by major clinics and drug labeling convert those targets into bands such as 15–24 kg = 1 tablet (3 mg), 25–35 kg = 2 tablets (6 mg), 36–50 kg = 3 tablets (9 mg), 51–65 kg = 4 tablets (12 mg), and 66–79 kg = 5 tablets (15 mg), with some labels shifting the top band to a mg/kg calculation beyond a certain weight (for example ≥ 80 kg) — these bandings are reflected in Mayo Clinic and other dosage charts [1] [6] [7].
4. Example calculation to demonstrate the conversion
For a 60 kg person at a 200 mcg/kg target the calculation is 60 kg × 200 mcg/kg = 12,000 mcg total, divided by 3,000 mcg per tablet = 4 tablets (12 mg), which matches standard table entries [1] [4]; for the same person at 150 mcg/kg the math gives 9,000 mcg → 3 tablets (9 mg), mirroring onchocerciasis tables [2] [3].
5. How rounding and weight bands balance precision with practicality
Tables intentionally round to whole tablets and create bands so clinicians can dose quickly without tablet splitting; that causes small deviations from the exact mcg/kg target — usually within clinical tolerance for labeled indications — and many manufacturers/labels transition to mg/kg rules once patients exceed the highest practical tablet band to avoid excessive rounding error [2] [3] [1].
6. Variations, special cases and repeated dosing
Some conditions call for repeated doses or slightly different per‑kilogram targets (for example scabies regimens or higher experimental doses used in trials), so tables may show repeat schedules or different bands; trial protocols and therapeutic cheat sheets sometimes use 150–250 mcg/kg ranges or multiple-day regimens that require per‑weight tablet counts adjusted across days [5] [8].
7. Common sources of confusion and cautionary notes
Confusion arises when people try to apply veterinary formulations or nonstandard tablet strengths — clinical tables and product labels emphasize human 3 mg tablets and warn against nonmedical formulations — and online shortcuts (like “divide pounds by 33”) are simplifications that risk dosing errors; authoritative labels and clinic guidance must be followed [3] [9] [10].
8. Bottom line for clinicians and caregivers
Dosing tables are a practical translation of mcg/kg prescriptions into whole 3 mg tablets: calculate mg needed from weight × mcg/kg, convert to tablets by dividing by 3 mg, then use validated weight bands from trusted labels or clinical sources (Mayo Clinic, FDA/labeling, professional guides) to select the nearest whole‑tablet dose while noting indications and repeat‑dose rules [1] [2] [4].