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Cytomel (Liothyronine Sodium)
Thyroid hormones bind nuclear receptors to control DNA transcription and protein synthesis.
Liothyronine sodium (Cytomel) is a synthetic T3 thyroid hormone indicated for hypothyroidism replacement, TSH suppression in thyroid cancer management, and diagnostic thyroid suppression testing. The drug is rapidly absorbed (95% in 4 hours) with a 2.5-day half-life and works by binding nuclear thyroid receptors to regulate gene transcription. Major risks include hyperthyroidism from overdosage causing cardiac arrhythmias, myocardial infarction, and tremors, plus contraindication in uncorrected adrenal insufficiency. Multiple drug interactions affect absorption and protein binding, requiring careful monitoring and dosing adjustments.
At a glance
| Generic name | Liothyronine Sodium |
|---|---|
| Sponsor | Pfizer Inc. |
| Drug class | Thyroid hormone replacement |
| Target | Thyroid receptor proteins attached to DNA |
| Modality | Small molecule |
| Therapeutic area | Other |
| Phase | FDA-approved |
Mechanism of action
Liothyronine sodium (T3) is a synthetic thyroid hormone that diffuses into cell nuclei and binds to thyroid receptor proteins attached to DNA. This hormone-receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. The physiological actions of thyroid hormones are produced predominantly by T3, with approximately 80% of circulating T3 derived from T4 by deiodination in peripheral tissues.
Approved indications
- Hypothyroidism
- Pituitary Thyroid-Stimulating Hormone (TSH) Suppression
- Thyroid Suppression Test
Boxed warnings
- WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS • Thyroid hormones, including CYTOMEL, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. • In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. • Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those use
Common side effects
- Arrhythmias
- Myocardial infarction
- Dyspnea
- Headache
- Nervousness
- Irritability
- Insomnia
- Tremors
- Muscle weakness
- Increased appetite
- Weight loss
- Diarrhea
Serious adverse events
- Cardiac arrest
- Heart failure
- Angina
- Pseudotumor cerebri
- Slipped capital femoral epiphysis
- Craniosynostosis
- Angioedema
- Serum sickness
- Muscle cramps
- Vomiting
Drug interactions
- Bile Acid Sequestrants (Colesevelam, Cholestyramine, Colestipol)
- Ion Exchange Resins (Kayexalate, Sevelamer)
- Clofibrate, Estrogen-containing oral contraceptives, Estrogens (oral), Heroin/Methadone, 5-Fluorouracil, Mitotane, Tamoxifen
- Androgens/Anabolic Steroids, Asparaginase, Glucocorticoids, Slow-Release Nicotinic Acid
- Salicylates (>2 g/day)