Thyroxine L

Levothyroxine sodium (T4) for hypothyroidism in dogs, cats, and horses. Levothyroxine sodium (synthetic thyroxine / T4). Mechanism: prohormone converted to bioactive T3 in peripheral tissues via 5'-deiodinase. T3 binds nuclear thyroid hormone receptors (TR-α, TR-β) → regulates transcription of genes controlling basal metabolic rate, thermogenesis, cardiac function, bone turnover, and neurological development. Key information Levothyroxine — see levothyroxine entry. Administer consistently.

Oral: Administer orally. May be given with food to improve compliance and reduce GI upset. on empty stomach (30–60 min before feeding). Separate from antacids, calcium, iron. Measure T4 level 4–6 hrs post-dose. Store at room temperature; protect from light. If a dose is missed Administer as soon as you remember. If it is almost time for the next scheduled dose, skip the missed dose and resume the normal schedule. Never double up doses to make up for a missed one. A single missed dose is unlikely to cause immediate clinical problems.

Thyrotoxicosis (overdose): tachycardia, hypertension, panting, polyphagia, weight loss, excitability, diarrhea. Cardiac arrhythmias. Monitor serum T4 levels.

For animals Monitor T4 levels and clinical signs. See levothyroxine precautions. For people handling this medication Wash hands thoroughly with soap and water after handling. Avoid contact with eyes; if contact occurs, flush with water for 15 minutes and seek medical attention. Keep out of reach of children. If accidental ingestion occurs, contact Poison Control (1-800-222-1222). Thyroid hormone — Wash hands thoroughly with soap and water after handling. after handling. Keep away from children. Do not use animal thyroid hormone as human replacement.

Contact your veterinarian. Levothyroxine overdose causes hyperthyroid-like signs.