liothyronine sodium (T₃)
Cytomel, Triostat

Available forms
Available by prescription only
Injection: 10 mcg/ml
Tablets: 5 mcg, 25 mcg, 50 mcg

Indications and dosages
 Congenital hypothyroidism. Children: 5 mcg P.O. daily, increased by 5 mcg q 3 to 4 days until desired response occurs.
 Myxedema. Adults: Initially, 5 mcg daily, increased by 5 to 10 mcg q 1 to 2 weeks. Maintenance dosage is 50 to 100 mcg daily.
 Myxedema coma, precoma. Adults: Initially, 25 to 50 mcg I.V.; reassess after 4 to 12 hours, then switch to P.O. as soon as possible. Patients with known or suspected cardiac disease should receive 10 to 20 mcg I.V.
 Nontoxic goiter. Adults: Initially, 5 mcg P.O. daily; may be increased by 5 to 10 mcg daily at intervals of 1 to 2 weeks until dosage of 25 mcg daily is reached. Thereafter, dosage may be increased by 12.5 to 25 mcg daily at intervals of 1 to 2 weeks until desired response is noted. Usual maintenance dosage is 75 mcg daily.
Adults older than age 65: Initially, 5 mcg P.O. daily, increased by 5-mcg increments q 1 to 2 weeks until desired response is obtained.
Children: Initially, 5 mcg P.O. daily, increased by 5-mcg increments at weekly intervals until desired response is achieved.
 Thyroid hormone replacement. Adults: Initially, 25 mcg P.O. daily, increased by 12.5 to 25 mcg q 1 to 2 weeks until satisfactory response is achieved. Usual maintenance dosage is 25 to 75 mcg daily.
 Liothyronine suppression test to differentiate hyperthyroidism from euthyroidism. Adults: 75 to 100 mcg daily for 7 days.

Pharmacodynamics
Thyroid hormone replacement: Liothyronine is usually a second-line drug in the treatment of hypothyroidism, myxedema, and cretinism. This component of thyroid hormone affects protein and carbohydrate metabolism, promotes gluconeogenesis, increases the utilization and mobilization of glycogen stores, stimulates protein synthesis, and regulates cell growth and differentiation. The major effect of liothyronine is to increase the metabolic rate of tissue. It may be most useful in syndromes of thyroid hormone resistance.

Pharmacokinetics
Absorption: About 95% is absorbed from the GI tract.
Distribution: Highly protein-bound. Its distribution hasn’t been fully described.
Metabolism: Not fully understood.
Excretion: Half-life is 1 to 2 days.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug and in those with acute MI uncomplicated by hypothyroidism, untreated thyrotoxicosis, or uncorrected adrenal insufficiency.
  Use cautiously in elderly patients and in patients with angina pectoris, hypertension, ischemia, other CV disorders, renal insufficiency, diabetes, or myxedema.

Interactions
Drug-drug. Adrenocorticoids, corticotropin: Alters thyroid status. Change in liothyronine dosage may require change in adrenocorticoid or corticotropin dosage.
Anticoagulants: Alters PT and INR. Monitor patient for potential dosage adjustment.
Estrogens: Increases thyroxine-binding globulin levels. May increase liothyronine requirements. Monitor patient’s need for dosage adjustment.
Insulin, oral antidiabetics: May affect dosage requirements of these drugs. Monitor patient for need for dosage adjustment.
Sympathomimetics, tricyclic antidepressants: May increase effects of these drugs, causing coronary insufficiency or arrhythmias. Use together cautiously.

Adverse reactions
CNS: nervousness, insomnia, tremor, headache.
CV: tachycardia, arrhythmias, angina pectoris, cardiac decompensation and collapse.
GI: diarrhea, vomiting.
GU: menstrual irregularities.
Metabolic: weight loss.
Musculoskeletal: accelerated bone maturation in infants and children.
Skin: diaphoresis, skin reactions.
Other: heat intolerance.

Effects on lab test results
None reported.

Overdose and treatment
Evidence of overdose reflects hyperthyroidism and may include weight loss, increased appetite, palpitations, diarrhea, nervousness, abdominal cramps, sweating, headache, tachycardia, increased blood pressure, widened pulse pressure, angina, arrhythmias, tremor, insomnia, heat intolerance, fever, and menstrual irregularities.
 Treatment reduces GI absorption and counteracts central and peripheral effects, primarily sympathetic activity. Use gastric lavage or induce emesis (followed by activated charcoal up to 4 hours after ingestion). If patient is comatose or having seizures, inflate the cuff on an endotracheal tube to prevent aspiration. Treatment may include oxygen and ventilation to maintain respiration. It also should include appropriate measures to treat heart failure and control fever, hypoglycemia, and fluid loss. Propranolol (or another beta blocker) may be used to counteract many of the effects of increased sympathetic activity. Withdraw liothyronine gradually over 2 to 6 days; then resume at a lower dosage.

Special considerations
• Liothyronine may be preferred when rapid effect is desired or when GI absorption or peripheral conversion of levothyroxine to liothyronine is impaired.
• Monitor thyroid studies to assess response to drug therapy.
• Oral absorption may be reduced in patients with heart failure.
• When switching from levothyroxine to liothyronine, discontinue levothyroxine and start liothyronine at low dosage, increasing in small increments after residual effects of levothyroxine have disappeared. When switching from liothyronine to levothyroxine, start levothyroxine several days before withdrawing liothyronine to avoid relapse.
• Liothyronine therapy alters radioactive iodine (¹³¹I) uptake, protein-bound iodine levels, and liothyronine uptake.
• Discontinue drug 7 to 10 days before patient undergoes radioactive iodine uptake studies.
Breast-feeding patients
• Minimal amounts of drug appear in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Partial hair loss may occur during first few months of therapy. Reassure child and parents that this is temporary. Infants and children may experience accelerated bone maturation.
Geriatric patients
• Elderly patients are more sensitive to effects of drug. For patients older than age 60, initial dosage should be 25% lower than usual recommended adult dosage.

Patient education
• Tell patient to report headache, diarrhea, nervousness, excessive sweating, heat intolerance, chest pain, increased pulse rate, or palpitations.
• Advise patient not to store drug in bathroom or other warm, humid areas to prevent deterioration of drug.
• Encourage patient to take drug at the same time each day, preferably in the morning to avoid insomnia.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use