What are the known toxic or lethal ivermectin dose ranges for dogs, cats, and humans and signs of overdose?
Executive summary
Ivermectin is safe at standard human doses (typically ~150–200 µg/kg single dose) but can cause neurologic and respiratory toxicity at much higher doses or when veterinary formulations are used; reported human ingestions ranged from ~6.8 mg up to 125 mg (veterinary pastes) in case series with hospitalizations (some required admission) [1] [2] [3]. In dogs and cats, clinical toxicosis appears at roughly 0.1–2.5 mg/kg (100–2,500 µg/kg) with sensitive breeds showing effects at the very low end — and lethal doses in animal experiments span tens of mg/kg [4] [5] [6].
1. What “normal” human doses look like — and how much higher the reported overdoses were
Approved human regimens for parasitic infections are small: typical single doses are in the range of 150–200 micrograms per kilogram (mcg/kg) of body weight (about 3 mg tablets for many adults) [7] [8]. Clinical studies deliberately tested far higher doses: volunteers received single doses up to 120 mg and repeated regimens (30–60 mg repeatedly) without consistent CNS toxicity up to ten times the FDA‑approved dose, but food increased exposure and accumulation was possible [1] [9]. Real‑world misuse during COVID‑19 involved people taking veterinary pastes or concentrated solutions; reported ingested amounts in one U.S. series ranged from 6.8 mg to 125 mg for veterinary paste and 20–50 mg for 1% solutions, with six of 21 callers hospitalized [2] [3].
2. Human overdose signs and clinical course
When overdoses occur, the dominant problems are neurologic and respiratory: altered mental status, ataxia, tremor, blurred vision/mydriasis, seizures, coma and, in severe cases, respiratory depression requiring support [10] [11]. Case series and reviews stress that treatment is supportive — there is no universally accepted antidote — and clinical management focuses on airway and respiratory support, seizure control and monitoring for complications [10] [11]. The literature also notes special risks in areas with Loa loa co‑infection, where post‑treatment neurologic events have been reported with standard doses [11].
3. Dogs and cats — where toxicity thresholds are much lower and genetics matter
Veterinary guidance and toxicology reviews place clinical toxicosis for dogs and cats roughly between 0.1 and 2.5 mg/kg (100–2,500 µg/kg), with many sources noting signs commonly at >2 mg/kg in typical dogs while genetically susceptible breeds (MDR1/ABCB1 mutation: collies, Australian shepherds, Shetlands, etc.) can show severe signs at ~0.1 mg/kg [4] [5]. Cats have reported clinical signs at about 0.3–0.4 mg/kg [5]. Typical clinical signs in pets include lethargy, ataxia, tremors, hypersalivation, mydriasis, blindness, respiratory depression and seizures; severe cases can progress to coma and death [12] [13] [14].
4. Lethal doses in animals and limitations extrapolating to humans
Laboratory LD50s vary widely by species: mice ~25 mg/kg, dogs ~80 mg/kg in older compilations, experimental IV doses causing severe depression or death in rats occurred in the single‑digit mg/kg to tens of mg/kg range [15] [6] [16]. These animal LD50 figures cannot be directly translated to safe human thresholds without caveats; some human volunteer work increased doses to 2 mg/kg or single oral doses up to 120 mg with limited severe toxicity, but reports of toxicity in real‑world misuse and species differences in blood‑brain barrier and P‑glycoprotein function make extrapolation hazardous [1] [16] [6].
5. Treatment approaches and controversies
Treatment in animals and humans is principally supportive; intravenous lipid emulsion (ILE) has been used in veterinary cases with apparent benefit for severe intoxication and has been described in case reports for large‑animal and canine overdoses [17] [12]. Human toxicology reviews and emergency medicine guidance emphasize supportive care and note that no standard antidote exists in routine practice [10]. Some older experimental antidotes (GABA antagonists) have severe side effects and are not routine [18].
6. How to interpret and act on this information
Public health and clinical sources uniformly warn against using animal ivermectin products in people because those formulations are more concentrated and untested for human safety; multiple authorities documented increased poison‑control calls during waves of misuse [19] [2] [8]. If exposure or suspected overdose occurs, consult poison control or an emergency clinician immediately; veterinary patients with any signs after exposure require urgent vet care [14] [3].
Limitations and open points: available sources document ranges and case series but do not establish a single definitive “lethal mg/kg” threshold for humans; animal LD50 values are variable and species‑specific and cannot be directly mapped to human lethal doses without further study [15] [16]. Sources disagree on exact safety margins for high human doses tested in trials versus real‑world overdoses, so clinicians treat exposures case‑by‑case [1] [3] [9].