Triostat (Liothyronine Sodium Injection) - Drug Interactions, Contraindications, Overdosage, etc

DRUG INTERACTIONS

Oral Anticoagulants

Thyroid hormones appear to increase catabolism of vitamin K-dependent clotting factors. If oral anticoagulants are also being given, compensatory increases in clotting factor synthesis are impaired. Patients stabilized on oral anticoagulants who are found to require thyroid replacement therapy should be watched very closely when thyroid is started. If a patient is truly hypothyroid, it is likely that a reduction in anticoagulant dosage will be required. No special precautions appear to be necessary when oral anticoagulant therapy is begun in a patient already stabilized on maintenance thyroid replacement therapy.

Insulin or Oral Hypoglycemics

Initiating thyroid replacement therapy may cause increases in insulin or oral hypoglycemic requirements. The effects seen are poorly understood and depend upon a variety of factors such as dose and type of thyroid preparations and endocrine status of the patient. Patients receiving insulin or oral hypoglycemics should be closely watched during initiation of thyroid replacement therapy.

Estrogen, Oral Contraceptives

Estrogens tend to increase serum thyroxine-binding globulin (TBG). In a patient with a nonfunctioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine may be decreased when estrogens are started thus increasing thyroid requirements. However, if the patient's thyroid gland has sufficient function, the decreased free thyroxine will result in a compensatory increase in thyroxine output by the thyroid. Therefore, patients without a functioning thyroid gland who are on thyroid replacement therapy may need to increase their thyroid dose if estrogens or estrogen-containing oral contraceptives are given.

Tricyclic Antidepressants

Use of thyroid products with imipramine and other tricyclic antidepressants may increase receptor sensitivity and enhance antidepressant activity; transient cardiac arrhythmias have been observed. Thyroid hormone activity may also be enhanced.

Digitalis

Thyroid preparations may potentiate the toxic effects of digitalis. Thyroid hormonal replacement increases metabolic rate, which requires an increase in digitalis dosage.

Ketamine

When administered to patients on a thyroid preparation, this parenteral anesthetic may cause hypertension and tachycardia. Use with caution and be prepared to treat hypertension, if necessary.

Vasopressors

Thyroid hormones increase the adrenergic effect of catecholamines such as epinephrine and norepinephrine. Therefore, use of vasopressors in patients receiving thyroid hormone preparations may increase the risk of precipitating coronary insufficiency, especially in patients with coronary artery disease. Therefore, use caution when administering vasopressors with liothyronine (T₃).

OVERDOSAGE

Signs and Symptoms

Headache, irritability, nervousness, tremor, sweating, increased bowel motility and menstrual irregularities. Angina pectoris, arrhythmia, tachycardia, acute myocardial infarction or congestive heart failure may be induced or aggravated. Shock may also develop if there is untreated pituitary or adrenocortical failure. Massive overdosage may result in symptoms resembling thyroid storm.

Treatment of Overdosage

Dosage should be reduced or therapy temporarily discontinued if signs and symptoms of overdosage appear. Treatment may be reinstituted at a lower dosage. In normal individuals, normal hypothalamic-pituitary-thyroid axis function is restored in six to eight weeks after cessation of therapy following thyroid suppression.

Treatment is symptomatic and supportive. Oxygen may be administered and ventilation maintained. Cardiac glycosides may be indicated if congestive heart failure develops. Beta-adrenergic antagonists have been used advantageously in the treatment of increased sympathetic activity. Measures to control fever, hypoglycemia or fluid loss should be instituted if needed.

CONTRAINDICATIONS

Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency or untreated thyrotoxicosis. Thyroid hormone preparations are also generally contraindicated in patients with hypersensitivity to any of the active or extraneous constituents of these preparations; however, there is no well-documented evidence in the literature of true allergic or idiosyncratic reactions to thyroid hormone.

Concomitant use of Triostat and artificial rewarming of patients is contraindicated. (See PRECAUTIONS.)