ExoticRx · exoticrx.com/drugs/methimazole
US brand names:Tapazole, Felimazole
Methimazole is dosed at 0.5–2 mg/kg PO q24h in guinea pigs, per Mayer J, Wagner R, Taeymans O. Advanced diagnostic approaches and current management of thyroid pathologies in guinea pigs. Vet Clin North Am Exot Anim Pract. 2010;13:509-523. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.801 doi:10.1016/j.cvex.2010.05.009 — Carpenter's Exotic Animal Formulary 6th ed, Table 9.7 (Miscellaneous Agents Used in Rodents). The copy held is an ebook conversion with no printed page numbers, so the table — not the page — is the citable location. — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929. Verify against current literature before clinical use.
Inhibits thyroid peroxidase, blocking iodine organification and thyroid hormone synthesis. Does not destroy thyroid tissue.
Cats: monitor renal function (treating hyperthyroidism may unmask underlying renal disease). Side effects include anorexia, vomiting, facial pruritus, and blood dyscrasias. Monitor CBC and liver enzymes.
Species references:All Cat (Domestic) drugsAll Guinea Pig drugsAll Rabbit (Domestic) drugs
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A dog/cat sample is shown here. Cited dosing for all 3 species — reptiles, birds, pocket pets, livestock, and equine — is free on the per-species pages above. Pro adds the weight-based calculator for every species.
| Species | Route | Dose | Frequency | Evidence | Source |
|---|---|---|---|---|---|
| Cat (Domestic) | PO | 2.5 mg/cat (per animal - NOT mg/kg) | PO q12h; titrate 2.5 mg steps; max 20 mg/day | Strong | Plumb's Veterinary Drug Handbook, 10th ed (2023, held copy; the original seed cited the 9th, which was never consulted) — corpus p.878 (plumb), located 2026-08-05 by exact figure+drug match (closest match at 27 chars with species on page). — LOCATOR CONVENTION 2026-08-07: the bare 'p.878' in this citation is the PDF index of the held scan, not the printed page. The PRINTED page is p.851; verified by finding the drug named there. If you are holding the book, turn to p.851. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207 — Plumb's Veterinary Drug Handbook, 10th ed (held), Methimazole monograph, printed p.851 (corpus PDF p.878), CATS: "Hyperthyroidism (label dosage; FDA-approved): Starting dose is 2.5 mg/cat (NOT mg/kg) PO every 12 […]" [INDICATION CORRECTED 2026-08-12, two readers — no page in the cited book pairs methimazole with thyroidectomy.] |
| Cat (Domestic) | TRANSDERMAL | 2.5–5 mg per animal | q12h |
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View PlansSource citations and evidence levels available on the live page. Reference only — verify against current literature before clinical use.
| Plumb's Veterinary Drug Handbook, 10th ed (2023, held copy; the original seed cited the 9th, which was never consulted) — Plumb's 10th ed (held) printed p.849, Methimazole monograph spanning p.849-851; page located 2026-08-05 from the book's own running heads, verified to name the drug in its body text. — located 2026-08-05 in Plumb's 10th ed, Methimazole monograph, printed p.849-851; the earlier note claiming no held source contained this figure was wrong and has been removed. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207 |