What is the toxic dose of ivermectin for adults and children?
Executive summary
Therapeutic ivermectin dosing for most human indications is weight‑based, typically 150–200 micrograms (mcg/kg) as a single oral dose; some mass‑treatment programs have used up to 0.4 mg/kg once yearly (400 mcg/kg) [1] [2]. Reported human poisonings involved large single or repeated doses from veterinary products — examples include ingestions of 6.8–125 mg (paste) or 20–50 mg (solution) and prescription misuse such as 21 mg twice weekly — with hospitalizations and neurologic symptoms reported [3] [4]. Available sources do not give a single, universally agreed “toxic dose” threshold in mg/kg for adults and children; toxicity appears to depend on formulation, dose relative to recommended mcg/kg, age, comorbidities and whether veterinary versus human formulations were used [3] [4] [5].
1. Standard human dosing and safety margin
Clinical and prescribing references state recommended human doses are weight‑based: commonly 150–200 mcg/kg as a single oral dose for parasitic infections, with some programs and indications using repeated courses or higher annual doses such as 0.4 mg/kg once yearly in mass‑treatment campaigns [1] [2]. Controlled clinical trials have escalated doses in adults to much higher single doses (up to 120 mg in a trial) and reported good tolerability with no consistent CNS toxicity up to roughly ten times the highest FDA‑approved dose (200 mcg/kg) in healthy adults, indicating a relatively wide safety margin under trial conditions [6] [7].
2. What the case reports and poisonings show about “toxic” amounts
Case series from the COVID‑19 period show toxicity when people ingested veterinary formulations or took regimens far above recommended human doses: reported doses from veterinary paste or solution ranged from 6.8 mg to 125 mg (paste) and 20–50 mg (solution), and some people used human tablets at 21 mg twice weekly — these patterns produced gastrointestinal symptoms, neurotoxicity and hospitalizations [3] [4]. A poison‑control style case in a young child who ingested injectable ivermectin (100–130 mg) caused mydriasis, vomiting, somnolence and autonomic signs but the child recovered in days, underscoring variable outcomes even after large ingestions [5].
3. Why a single “toxic dose” number is not provided in the sources
Available sources repeatedly note dose‑response variability by formulation and population and do not state a single mg/kg cutoff that guarantees toxicity. Clinical trials demonstrating tolerability at multiples of approved doses (up to ~10×) coexist with real‑world poisonings from veterinary products at seemingly lower mg amounts; investigators attribute toxicity to higher-than‑recommended dosing, repeated use, or non‑human formulations rather than a strict mg/kg threshold [6] [7] [4]. Therefore, the literature collected here does not support giving a single absolute toxic dose for adults or children (not found in current reporting).
4. Children and infants: special concerns and limited data
Most product labels and guidance limit use in very small children; many sources state safety and efficacy have not been established for children under 15 kg, and dosing is weight‑based for children ≥15 kg [1] [8]. A pediatric ingestion case (16‑month‑old, ~15 kg) with 100–130 mg ingestion produced symptoms but recovered, indicating children can manifest CNS and autonomic effects after large exposures; formal toxic thresholds for infants are not provided in the sources [5] [1].
5. Clinical picture of ivermectin toxicity and risk factors
Reported clinical effects cluster as neurologic (altered mental status, ataxia), gastrointestinal, visual and autonomic signs; neurotoxicity was particularly noted among older adult patients and those who took veterinary formulations or unusually high doses [4] [3]. Trial data suggest food increases exposure (AUC) and repeated dosing can cause accumulation signals in pharmacokinetics, so co‑factors such as dose frequency, taking with food, drug interactions (P‑glycoprotein inhibitors) and hepatic function can raise risk [6] [9].
6. Practical takeaways and reporting limitations
If exposure is suspected, clinical management should be guided by local poison control and clinicians because severity varies with dose, formulation and patient factors; published series document hospitalizations from non‑prescribed or veterinary product use [3] [4]. The assembled sources do not define a single toxic mg/kg threshold for adults or children; they document recommended therapeutic ranges (150–200 mcg/kg), higher tolerated doses in trials, and real‑world poisonings tied to misuse of veterinary or excessive regimens [1] [6] [3]. Limitations: available reporting is heterogeneous (trial vs. case reports vs. mass‑treatment programs) and does not permit a single, universal “toxic dose” claim (not found in current reporting).