l-Thyroxine (T4, Levothyroxine)

l-Thyroxine (T4, Levothyroxine) In Dogs & Cats: Uses, Dosage and Side Effects

Overview

• Binds to specific intracellular receptors and alters gene expression.

Uses of l-Thyroxine (T4, Levothyroxine)

• Treatment of hypothyroidism.
• Cases with pre-existing cardiac disorders require lower doses initially.

Dose of l-Thyroxine (T4, Levothyroxine) in Dogs and Cats

Dogs, Cats:

• Hypothyroidism: 0.02–0.04 mg/kg/day. Alternatively, dose at 0.5 mg/m2 body surface area daily.
• The dose is given with food once or divided twice a day.
• Monitor serum T4 levels pre-dosing and 4–8 hours after dosing.

Side Effects of l-Thyroxine (T4, Levothyroxine) in Dogs and Cats

• Clinical signs of overdosage include tachycardia, excitability, nervousness and excessive panting.
• Can unmask Addison’s disease in patients with autoimmune polyglandular syndrome.

Contraindications of l-Thyroxine (T4, Levothyroxine) in Dogs and Cats

• Uncorrected adrenal insufficiency.

Some Notes:

• Thyroxine enhances the actions of catecholamines and sympathomimetics.
• Diabetic patients receiving thyroid hormones may experience altered insulin requirements; monitor carefully during therapy initiation.
• Estrogens may increase thyroid requirements by elevating thyroxine-binding globulin levels.
• Thyroid hormones may reduce the therapeutic effects of ciclosporin, digoxin, and digitoxin.
• Ketamine administration to patients on thyroid hormones may lead to tachycardia and hypertension.
• Numerous drugs may affect thyroid function tests, necessitating careful monitoring during therapy.