How do concentrations of ivermectin in horse paste compare to human formulations?

1. Horse paste versus human tablets: the raw concentration gap

Commercial horse paste products are explicitly manufactured at about 1.87% ivermectin by weight (each milligram of paste contains 0.0187 mg ivermectin), so a typical 6.07 g tube contains on the order of 113–114 mg of active drug; by contrast, human ivermectin pills are measured in single‑digit milligrams and prescribed on a microgram‑per‑kilogram basis (human dosing guidance commonly cited around 200 µg/kg) — in short, a single horse‑paste tube can contain the equivalent of dozens of human doses ^{[4] [1] [3] [2]}.

2. Different formulations, different pharmacology and risks

The human product is usually a swallowed tablet with pharmacokinetic data and dosing tied to human studies, while veterinary products include concentrated pastes, injectables and pour‑ons with different excipients and absorption patterns; those formulation differences affect peak blood levels (Cmax) and time to peak (tmax), and make extrapolating safety from animal products to humans unreliable ^{[5] [6] [7]}.

3. Clinical context: what “dose” means for safety

Clinical and veterinary experts emphasize ivermectin’s therapeutic window is defined by controlled, weight‑based human dosing; exceeding those exposures — for example by taking multiple doses or ingesting a veterinary tube intended for a large animal — raises the probability of gastrointestinal, neurological, and other toxic effects because plasma concentrations scale with the amount taken and can accumulate with repeated dosing ^{[5] [7]}.

4. What regulators and public‑health authorities warn about

Regulatory labels and university health experts warn explicitly that animal ivermectin products are not for human use, that inactive ingredients and concentrations may be unsafe for people, and that animal formulations carry package warnings and labels instructing against human ingestion ^{[8] [9] [6]}.

5. Extremes, examples and how the math looks

Published calculations used in public reporting illustrate the scale: researchers estimating human equivalent lethal doses found figures dramatically higher than standard human treatment doses (one cited “human equivalent” toxic estimate was 43,240 µg/kg versus typical 200 µg/kg therapeutic dosing), and popular breakdowns show a 150‑lb person would need very large numbers of human tablets or many complete horse‑paste tubes to reach that theoretical lethal amount — but those abstract calculations do not make animal paste safe for people because sublethal toxicity and formulation hazards remain real ^{[10] [3] [1]}.

6. Counterclaims and where reporting can mislead

Proponents sometimes point out that the active compound is chemically identical across formulations and that some livestock medicines use high‑quality manufacturing; those facts are true but incomplete — purity, excipients, dose per unit, intended species pharmacokinetics, and lack of human dosing studies for veterinary products are the reasons clinicians and regulators say veterinary ivermectin is not an acceptable substitute for a prescribed human formulation ^{[11] [8] [5]}.

7. Bottom line and practical implication

For anyone assessing risk, the clear technical point is that horse paste contains far higher amounts of ivermectin per unit than human tablets and is formulated differently, so substitution risks overdose, unpredictable blood levels, and adverse reactions — authorities therefore advise using only human‑labeled, prescription ivermectin when medically indicated and under clinician direction ^{[4] [2] [8]}.