How do veterinary authorities recommend calculating ivermectin dose by weight and species?
Executive summary
Veterinary authorities and product labels recommend dosing ivermectin primarily by species and body weight, expressed as micrograms or milligrams per kilogram; common target ranges are about 100–600 mcg/kg depending on species and indication, with specific licensed doses such as 200 mcg/kg for cattle and 300 mcg/kg for swine [1] [2] [3]. Calculating a correct dose requires converting the patient’s weight to kilograms, multiplying by the indicated mcg/kg (or mg/kg) and then matching that total to the formulation strength (tablet mg or injectable mg/mL), while always observing species-specific safety considerations such as MDR1 sensitivity in certain dog breeds [4] [3].
1. How dose recommendations are expressed — mcg/kg and mg/kg, not “one size fits all”
Dose recommendations in veterinary and human guidance are given per unit body weight—most commonly micrograms per kilogram (mcg/kg) or milligrams per kilogram (mg/kg)—because ivermectin’s therapeutic and toxic windows vary by species and condition; for example, many veterinary texts note a single-dose efficacy at about 0.1 mg/kg (100 mcg/kg) for sheep and cattle [3] while labelled cattle injectable products are formulated to deliver 200 mcg/kg subcutaneously [1] [2].
2. Common, licensed veterinary doses by species and formulation
Commercial injectable ivermectin for cattle is typically labeled to deliver 200 mcg ivermectin per kilogram by subcutaneous injection (with product concentration often 10 mg/mL so 1 mL treats ~50 kg) and swine labels commonly recommend 300 mcg/kg administered in the neck subcutaneously [1] [2]. For horses, oral pastes are calibrated to deliver roughly 200 mcg/kg (often presented as 91 mcg per lb on syringe labels, which corresponds to ~200 mcg/kg) for parasite control [5]. Dogs and cats use much lower preventive doses for heartworm (for example monthly heartworm preventives may deliver 0.03–0.06 mg total for a 20‑lb dog depending on product), while therapeutic doses for mange or other infestations can be higher and require veterinary supervision [6] [4].
3. Practical calculation method used by clinicians
The standard calculation method is: convert animal weight to kilograms, multiply by the species- and indication-specific dose in mcg/kg (or mg/kg) to get the total drug mass, then convert to the formulation unit (milligrams or mL) to determine tablets, chewables, paste syringes, or milliliters of injectable [1] [7]. For example, a 500‑kg cow at a label dose of 200 mcg/kg requires 100,000 mcg = 100 mg; with a 10 mg/mL injectable that equals 10 mL [1]. For humans, clinicians commonly use approximately 150–200 mcg/kg (some guidelines use 150 mcg/kg, others 200 mcg/kg) and Stromectol tablets are 3 mg each so practitioners calculate the number of tablets from the patient’s weight [7] [8] [9].
4. Safety caveats, off‑label use, and breed/species sensitivities
Veterinary sources warn that species differ dramatically in sensitivity: some dog breeds with the MDR1 (ABCB1) mutation can show severe neurotoxicity at doses that are tolerated in other dogs, and accidental use of high‑concentration livestock formulations in small animals has caused poisoning [3] [5]. Product labels and veterinary guidance emphasize using species‑specific, veterinary‑approved formulations and calibrated dosing tools, and reserving higher therapeutic regimens for veterinary supervision [2] [4].
5. Where guidance diverges and reporting limits
Published human and veterinary references show overlapping but not identical dose ranges—human therapeutic practice commonly cites 150–200 mcg/kg for parasitic diseases [8] [10], whereas veterinary labels and textbooks present species‑specific recommendations such as 100 mcg/kg for some ruminants up to 300 mcg/kg for swine [3] [1]. Available sources here do not provide a single comprehensive table for every species, indication, and formulation; clinicians rely on product labeling, formularies, and veterinary judgment for exact regimens [1] [6].