What excipients and solvents in veterinary ivermectin increase toxicity risk for humans?
Executive summary
Veterinary ivermectin products pose increased human risk mainly because they are formulated at much higher doses and in non-oral routes (injectable, pour‑on, paste), and because some veterinary preparations include untested secondary actives or excipients such as clorsulon or solvents not intended for humans [1] [2]. Case reports show severe neurotoxicity after use of veterinary formulations — including an intravenous veterinary product producing a serum ivermectin concentration of 187.74 ng/mL and clinical ICU admission — and reviews of poisonings link veterinary formulations with larger ingested doses and worse outcomes [3] [4] [2].
1. Why veterinary formulations are intrinsically riskier: dose form and route designed for animals
Veterinary ivermectin comes as high‑concentration pour‑ons, pastes and injectables for large animals; those forms often deliver much larger absolute doses or permit parenteral administration that human ivermectin never does, creating clear overdose risk when repurposed by people [2] [3]. The FDA and clinical reviews document that people who used veterinary products tended to ingest larger single or repeated doses and experienced more hospitalizations than those using human tablets [4] [2].
2. Solvents, excipients and “secondary actives”: the unknown chemical hazards
Analytical work shows some veterinary preparations include excipients or secondary actives — for example clorsulon is named as a secondary active present in some products — that are not tested for human safety and could have independent toxicity or interact with ivermectin [1]. Published warnings and consumer guidance stress excipients in veterinary products may cause allergic reactions, organ toxicity or other systemic harms in humans [5] [1].
3. Parenteral veterinary products: a special danger demonstrated by a published case
Human ivermectin is available only orally; veterinary pharmacopeia permits subcutaneous or intravenous routes. A confirmed case report describes a patient who received repeated oral doses plus an intravenous veterinary ivermectin product and developed severe neurotoxicity requiring ICU care, with a measured toxic serum ivermectin concentration of 187.74 ng/mL — the report attributes the severity to high oral dosing combined with intravenous administration of veterinary product [3].
4. Formulation solvents and carriers can change pharmacokinetics and toxicity
Formulation choices — solvents, lipid carriers, injectables, nanomedicine approaches — alter how ivermectin is absorbed, distributed and cleared; veterinary solvents designed to deliver drug rapidly into large animals or through skin can increase systemic exposure or enable routes that bypass first‑pass metabolism, raising human toxicity risk [6] [7]. Veterinary pour‑ons or injectables are formulated for animal physiology and may deliver more bioavailable drug in humans than an equivalent oral tablet would [6] [8].
5. Clinical picture and observed harms linked to veterinary products
Reviews and case series of ivermectin misuse for COVID‑19 found that persons using veterinary products reported doses from low mg paste to tens of mg solution and had a disproportionate share of hospitalizations and severe neurologic symptoms (ataxia, seizures, depressed consciousness); one review identified a death among cases and multiple hospital admissions tied to veterinary formulations [2] [4]. Veterinary product misuse is repeatedly implicated in severe outcomes [8] [2].
6. What the testing data show — and what’s not reported
Quantification studies found ivermectin content in tested veterinary products was within labeled limits, yet investigators still warned against human use because of high dosages, untested excipients and secondary actives like clorsulon that may have unknown long‑term impacts in humans [1]. Available sources do not mention a comprehensive list of specific solvents/excipients across brands nor systematic toxicology data for every veterinary excipient in humans — gaps that increase uncertainty [1].
7. Practical takeaway: the real hazards to avoid
Avoid using veterinary ivermectin in humans because formulations are higher dose, can contain untested additives (e.g., clorsulon), and include non‑oral routes (injectable, intravascular, pour‑on) that have produced severe neurotoxicity in case reports [1] [3] [2]. Public health guidance and clinical reviews document increased hospitalizations and neurologic harms tied to veterinary products and urge use only of regulated human formulations under medical supervision [4] [8].
Limitations: reporting is largely case series, product surveys and reviews; systematic toxicology of every veterinary excipient in humans is not available in these sources, and newer formulation science (nanomedicine) is evolving with separate regulatory tracks for human vs. veterinary uses [6] [1].