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What are safe human ivermectin dosages for approved indications (e.g., parasitic infections) and how do they vary by weight and age?
Executive summary
Approved human ivermectin dosing is weight‑based and condition‑specific: for onchocerciasis typical single doses are about 150 micrograms/kg and for strongyloidiasis about 200 micrograms/kg; product labeling and major clinical references give single‑dose tables and weight bands used in practice (e.g., 3 mg increments for tablets) [1] [2] [3]. Children ≥15 kg are included in standard labeling with the same mcg/kg approach, while newer trials have tested 3 mg in younger children (10–14 kg) for scabies with acceptable exposure and tolerability — but routine labeling historically restricted use to ≥15 kg [2] [4] [1].
1. How approved doses are expressed — mcg/kg, not a flat pill rule
Regulatory and clinical sources express ivermectin dosing as micrograms per kilogram of body weight: onchocerciasis (river blindness) dosing is approximately 150 mcg/kg as a single oral dose, and strongyloidiasis dosing is approximately 200 mcg/kg as a single oral dose [1] [5]. Many clinical guides translate those per‑kg doses into practical tablet counts and weight bands (for example, Drugs.com lists 3 mg tablets with weight bands such as 15–25 kg = 3 mg, 26–44 kg = 6 mg, etc.) to simplify prescribing [3] [6].
2. Typical adult and pediatric regimens used in practice
Common practice for most parasitic indications uses single‑dose therapy often between 0.15 and 0.25 mg/kg (150–250 mcg/kg), sometimes rounded to available tablet strengths (3 mg, 6 mg, 12 mg). For scabies or lice, repeated or higher short courses are used (e.g., crusted scabies regimens involve multiple doses such as 0.2 mg/kg on days 1, 2 and 8) [7] [3] [8]. The FDA product information and Dailymed recommend dosing tables to provide approximately 150 mcg/kg for onchocerciasis and about 200 mcg/kg for strongyloidiasis [1].
3. How dosing varies by weight — practical weight bands and tablet counts
Because tablets come in fixed strengths, many prescribers use weight bands to determine tablet counts: example weight bands from clinical dosing charts convert the per‑kg target into rounded tablet totals (e.g., 15–25 kg → 3 mg; 26–44 kg → 6 mg; 45–64 kg → 9 mg; 65–84 kg → 12 mg; ≥85 kg → 0.15 mg/kg) [3] [6]. These bands reflect an attempt to deliver an approximate mcg/kg dose using available tablet strengths [3].
4. Age considerations and the lower weight limit
Labeling and major references historically limit standard oral ivermectin use to adults and children weighing at least 15 kg; dosing for children ≥15 kg follows the same mcg/kg approach as adults [2] [5]. However, recent clinical trial data show that a single 3 mg dose in children aged 2–4 years weighing 10–14 kg produced plasma exposure comparable to older children and was effective and well tolerated for scabies, suggesting expanding evidence for lower‑weight children in specific settings [4]. Routine labeling and guidelines may lag such trial findings; check local guidance and product labeling before use [2] [4].
5. Condition‑specific differences and repeat dosing
Approved indications differ: onchocerciasis often uses 150 mcg/kg with retreatment intervals (commonly annually, sometimes sooner in heavy ocular disease), while strongyloidiasis uses ~200 mcg/kg as a single dose; scabies may require repeat or sequential dosing and higher cumulative exposure for crusted cases [1] [3] [7]. The number and timing of repeat doses vary by condition severity and guideline [3] [7].
6. Safety, special populations, and limitations of current reporting
Mayo Clinic notes clinical trials lacked sufficient numbers of people ≥65 to determine different responses but advises caution in elderly patients with liver, kidney, or heart disease [2]. Product labeling covers overdose management and pharmacology but available sources do not provide definitive universal upper daily limits beyond condition‑based regimens — instead clinicians rely on per‑kg targets and empirical schemes [1] [6]. Newer pediatric trial data are promising but not yet universally reflected in labeling; available sources do not mention that all jurisdictions have revised regulatory age/weight cutoffs accordingly [4] [2].
7. Practical takeaway and where to check before dosing
Use mcg/kg targets (≈150 mcg/kg for onchocerciasis; ≈200 mcg/kg for strongyloidiasis) and convert to tablet counts using manufacturer dosing tables or trusted dosing guides for the patient’s weight band [1] [3]. For children <15 kg, consult up‑to‑date clinical trial data and local guidelines — recent trials support specific 3 mg dosing in 10–14 kg children for scabies but routine labeling historically starts at 15 kg [4] [2]. Always follow product labeling, national guidance, and a prescriber’s judgment for special populations [1] [2].
Limitations: this summary uses the provided sources only; it does not assess unpublished data or regulatory changes outside these documents.