Levothyroxine

Updated on September 10, 2024

Synthetic thyroid hormone used to treat hypothyroidism.

Levothyroxine

Summary

Used For: Treatment of hypothyroidism

Brands: Thyro-Tabs Canine, Synthroid, Soloxine, Thyrosyn

Species: Dogs, cats, horses

Other names: L-Thyroxine

Drug type: Endocrine

Prescription required: Yes

Pregnancy and lactation: Use cautiously in pregnant animals. Safe to use in lactating animals.

Side effects: No side effects when used at an appropriate dose.

General description

Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism. [Buy Levothyroxine now on Petco.](https://www.petco.com/shop/en/petcostore/brand/thyro-tabs) A prescription from your veterinarian may be needed to purchase.

Uses

Levothyroxine is used to treat hypothyroidism in dogs, cats, and horses.

How it works

Levothyroxine works by replacing the amount of thyroxine that the pet is missing.

Dosage

**Dogs**: 0.02–0.04 milligrams per kilogram of body weight by mouth in single or divided doses. **Cats**: 0.05 – 0.2 milligrams per cat by mouth every 24 hours. Dosage is then adjusted by monitoring the T4 blood levels of the dog or cat every four weeks until an adequate maintenance dose is established. **Horses**: 0.01–0.1 milligrams per kilogram of body weight by mouth in a single or divided dose.

Forms

Levothyroxine Sodium Veterinary-labeled Tablets: 0.1 mg, 0.2 mg, 0.3 mg, 0.4 mg, 0.5 mg, 0.6 mg, 0.7 mg, 0.8 mg, & 1 mg. Levothyroxine Sodium Human-labeled Tablets: 0.025 mg, 0.05 mg, 0.075 mg, 0.088 mg, 0.1 mg, 0.112 mg, 0.125 mg, 0.137 mg, 0.15 mg, 0.175 mg, 0.2 mg & 0.3 mg. Levothyroxine oral solution 1 milligram per milliliter.

Storage information & handling

Tablets: store at room temperature protected from moisture and light. Oral solution: refrigerate and use within 2 months. Shake oral suspension well before use.

What results can I expect?

Resolution of signs associated with hypothyroidism.

Missed Dosage

Give the dose as soon as possible. If it is almost time for the next dose, skip the missed dose, and continue with the regular schedule. Never give two doses at once.

Overdose / acute toxicity

Chronic overdose will produce signs of hyperthyroidism.

Side effects

Rare when administered at appropriate dose and usually associated with overdosing. May include: * polyphagia * nervousness * elevated heart rate * excessive urinations * excessive drinking * excitability

Contraindications

Use with caution in geriatric patients as well as in patients with: * Known hypersensitivity * Thyrotoxicosis * Acute myocardial infarction * Adrenal insufficiency * Cardiac disease/hypertension * Diabetes Mellitus * Renal dysfunction

Drug interactions

Consult your veterinarian before using levothyroxine with any other medications, even vitamins and supplements. A high fiber diet may interfere with efficacy. The following drugs may interact with levothyroxine: * Amiodarone * Antacids * Antidepressants * Antidiabetic agents * Cholestyramine * Corticosteroids * Digoxin * Ferrous sulfate * Ketamine * Phenobarbital * Propylthiouracil * Rifampin * Sertraline * Sucralfate * Sympathomimetic agents * Warfarin

Precaution

Safety in pregnant animals has not been determined, use only when clearly necessary. Therapy should be gradual for patients with concurrent diseases. Wash hands after administering tablets. Pregnant women should handle tablets with caution.

Sources

*Plumb’s Veterinary Drug Handbook* *VIN Veterinary Drug Handbook*
image

Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Disclaimer

The information contained on this page is for educational purposes only. This medication should only be given under the advice of a veterinarian who has examined your pet under the laws applicable to your state of residence.