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One selection filters the source overview, clinical facts, reports and dose calculator. Literature references are not species-filtered.
Choose one species for its overview and dose calculator, or all species to browse the full evidence.
Source overview
Recorded excerpts for one species. Each dose remains a separate source entry; no regimen is selected.
Choose one species to view its source overview. All-species evidence remains available below.
View full clinical evidence and sources ↓Clinical evidence
Pending clinical review (PROPOSED)Rule-based (RULE_BASED)— applies to the facts and dose entries in this species selection; individual source records retain their own status.
Indications2
Hypothyroidism (replacement therapy)
DogCatExtra-label (EXTRA_LABEL)2 source records · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Hypothyroidism (replacement therapy) — Extra-label (no FDA-approved veterinary product)
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Hypothyroidism (replacement therapy) — Extra-label (no FDA-approved veterinary product)
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Dose regimens5
This calculator performs arithmetic only on the sourced dosing field shown for each result — it does not verify the field's accuracy, does not select which field to use for a patient, and does not replace a veterinarian's order. Not for clinical use. Confirm every result against the primary source before dispensing.
Choose one species above to view its dose calculator.
Adverse effects179
Tachycardia, polyphagia, PU/PD, excitability, panting (overdose signs) — Only with overdosing
DogNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
"Apathetic" hyperthyroidism (listlessness, anorexia) — ~10% of overdosed cats
CatNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
These are counts of spontaneously reported events, not proven adverse effects, causal relationships, or incidence rates.
Bars compare report counts within each species; they do not show incidence.
More reportsFewer reportsDog
- Vomiting437 reports
- Lethargy (see also Central nervous system depression in 'Neurological')329 reports
- Emesis306 reports
- Diarrhoea303 reports
- Lack of efficacy - NOS238 reports
- Weight loss204 reports
- Overdose185 reports
- Seizure NOS182 reports
- Panting181 reports
- Other abnormal test result NOS179 reports
- Anorexia173 reports
- Elevated alanine aminotransferase (ALT)173 reports
Cat
- Accidental exposure3 reports
- Vomiting3 reports
- Acute renal failure2 reports
- Ataxia2 reports
- Blood in urine2 reports
- Circumstance or info capable of leading to medication error2 reports
- Decreased urine concentration2 reports
- Drooling2 reports
- Elevated creatinine2 reports
- Elevated symmetrical dimethylarginine (SDMA)2 reports
- Emesis2 reports
- Hyperphosphataemia2 reports
Monitoring1
Serum T4 (trough, just prior to next dose, or peak 4–6h post-dose depending on protocol); clinical response
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Monitoring Parameters · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Contraindications1
Acute MI, thyrotoxicosis, untreated adrenal insufficiency
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Contraindications & Warnings table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Precautions4
Treated hypoadrenocorticism, cardiac disease, diabetes, geriatric patients — start low
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Contraindications & Warnings table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Brands are not necessarily bioequivalent (no FDA approval for veterinary products) — if switching brands or from tablet to liquid, retest T4 levels rather than assuming an equivalent dose.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Canine doses are much higher (per kg) than human doses — flag this explicitly if a human pharmacy is filling the prescription, to avoid under-dosing errors.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Reduce starting dose in older patients or those with cardiac disease/diabetes — start low, titrate up with monitoring.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Interactions5
Oral antacids, cholestyramine, ferrous sulfate, sucralfate, high-fiber diet — ↓ absorption — separate dosing by 4 hours
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Antidiabetic agents — ↑ insulin/oral hypoglycemic requirement
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Warfarin — ↑ anticoagulant effect
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Phenobarbital, rifampin — ↑ thyroxine metabolism — may need dose increase
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Tricyclic antidepressants — ↑ CNS stimulation/arrhythmia risk
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pharmacokinetics4
Bioavailability — Tablets ~37% avg (dog); oral liquid (Leventa) 150–200% more absorbed than tablets — dose adjustment needed when switching forms
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Half-life — ~12–16h (Plumb's) / ~20h (Papich), dog
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Metabolism — Peripheral conversion T4→T3
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Elimination — Minimal in milk
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pregnancy / lactation considerations1
Human FDA category A. Minimal excretion in milk — should not affect nursing offspring.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 724–726; Saunders Handbook of Veterinary Drugs (Papich), 4th ed., p. 445–447 — Pregnancy & Lactation · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Literature references19
References are linked to this drug. Species applicability is not recorded here, so the species filter does not narrow this list. Imported dates do not retain their original precision; confirm dates in the original citation.
- Thyroid function influences insulin requirements in patients with type 1 diabetes mellitus and chronic autoimmune thyroiditis: A cross-sectional study.
Study summary not available in the imported record. Open the original citation to review the study.
- Spontaneous adult-onset primary hypothyroidism in 17 cats.
Study summary not available in the imported record. Open the original citation to review the study.
- Survival of radioiodine treated hyperthyroid cats that are euthyroid and hypothyroid after treatment, and effect of levothyroxine supplementation on survival time of cats with iatrogenic hypothyroidism.
Study summary not available in the imported record. Open the original citation to review the study.
- Clinical hypothyroidism in a cat associated with sulfonamide administration for the management of intracranial nocardiosis.
Study summary not available in the imported record. Open the original citation to review the study.
- Thyroid hormones for euthyroid patients with simple goiter growing over time: a survey of European thyroid specialists.
Study summary not available in the imported record. Open the original citation to review the study.
Sources: PubMed, National Library of Medicine; openFDA, U.S. Food and Drug Administration; Plumb DC. Plumb's Veterinary Drug Handbook. 7th ed. PharmaVet Inc; 2011.
Owner information handout
Plain-language medication information to review with the owner. Open the handout to print it or download a PDF.
Available products
Products listed in the Health Canada Drug Product Database for this active ingredient. A listing does not establish that a product is authorized for the clinical uses described on this page.