Levothyroxine Powder

Synthetic T4 for hypothyroidism in dogs and horses; equine metabolic syndrome and PPID management. Synthetic thyroid hormone (L-thyroxine / T4). Mechanism: T4 is a prohormone converted to active triiodothyronine (T3) by deiodinases in target tissues → T3 binds nuclear thyroid hormone receptors → regulates gene transcription controlling metabolic rate, growth, cardiovascular function, and CNS development. Oral tablet or powder. Key information Thyroid hormone. Administer consistently (same time relative to meals). Narrow therapeutic index — recheck thyroid levels 4–8 weeks after starting. Store at room temperature; protect from light and humidity. Compounded powder: stability concerns — verify before dispensing.

Oral tablets (dogs): administer on an empty stomach, 30–60 min before feeding, for best absorption. Separate from antacids, calcium, iron, and fiber by 4 hrs. Compounded oral powder (horses): mix into a small portion of grain daily. Measure T4 levels 4–6 hrs post-pill in dogs. 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. Thyroid hormone levels are maintained over days — a single missed dose is unlikely to cause a clinical problem. Resume normal dosing.

Signs of thyrotoxicosis (overdose): tachycardia, panting, excitability, polyphagia, weight loss, diarrhea, hypertension, PU/PD. Cardiac arrhythmias (horses — with overdose). Dose adjustments required; monitor T4 levels 4–6 hrs post-dose.

For animals Monitor serum T4 (total T4 or free T4) 4–6 hrs post-pill in dogs, 6 hrs in horses. Target T4 in mid-to-high normal range at peak. Signs of thyrotoxicosis (overdose): tachycardia, PU/PD, weight loss, anxiety — reduce dose. Drug interactions: antacids, iron, calcium reduce absorption (separate by 4 hrs). Absorption may vary between products — do not switch brands without rechecking levels. 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. Accidental ingestion may cause tachycardia, palpitations. Do not use animal thyroid medications as human thyroid replacement.

Contact your veterinarian. Levothyroxine overdose causes signs of hyperthyroidism: increased heart rate, weight loss, excessive thirst, hyperactivity, and GI signs. Contact your veterinarian, a veterinary emergency clinic, or the ASPCA Animal Poison Control Center (888-426-4435) immediately. Do not induce vomiting unless specifically directed by a veterinary professional.