Pharmacologic class: Synthetic thyroid hormone
Therapeutic class: Thyroid hormone replacement
Pregnancy risk category A
FDA Box Warning
• Drug has been used (alone or with other agents) to treat obesity. In euthyroid patients, doses within range of daily hormonal requirements are ineffective for weight loss. Larger doses may produce serious or even life-threatening toxicity, particularly when given with sympathomimetic amines (such as those used for anorectic effects).
Increases basal metabolic rate, helps regulate cell growth and differentiation, and enhances metabolism of lipids, proteins, and carbohydrates
Tablets: 12.5 mcg levothyroxine sodium and 3.1 mcg liothyronine sodium (Thyrolar-¼); 25 mcg levothyroxine sodium and 6.25 mcg liothyronine sodium (Thyrolar-½); 50 mcg levothyroxine sodium and 12.5 mcg liothyronine sodium (Thyrolar-1); 100 mcg levothyroxine sodium and 25 mcg liothyronine sodium (Thyrolar-2); 150 mcg levothyroxine sodium and 37.5 mcg liothyronine sodium (Thyrolar-3)
Indications and dosages
Adults: All dosages individualized. Initially, one tablet Thyrolar-½ P.O., increased by one tablet Thyrolar-¼ P.O. daily until desired effect occurs. Usual maintenance dosage is one tablet Thyrolar-1 or Thyrolar-2 P.O. daily, adjusted within first 4 weeks based on laboratory results.
➣ Congenital hypothyroidism
Children older than age 12: 18.75/75 mcg P.O. daily
Children ages 6 to 11: 12.5/50 to 18.75/75 mcg P.O. daily
Children ages 1 to 5: 9.35/37.5 to 12.5/50 mcg P.O. daily
Children ages 6 to 12 months: 6.25/25 to 9.35/37.5 mcg P.O. daily
Children up to 6 months: 3.1/12.5 to 6.25/25 mcg (Thyrolar-¼) P.O. daily
• Severe, long-standing hypothyroidism
• Cardiovascular disease
• Psychosis or agitation
• Elderly patients
• Hypersensitivity to drug or its components
• Acute myocardial infarction
• Uncorrected thyrotoxicosis
• Uncorrected adrenal insufficiency and coexisting hypothyroidism
Use cautiously in:
• cardiovascular disease, severe renal insufficiency, diabetes mellitus, uncorrected adrenocortical disorders
• elderly patients
• pregnant or breastfeeding patients.
• Know that all dosages are highly individualized.
• Administer single daily dose in morning with or without food.
CNS: insomnia, irritability, nervousness, headache
CV: angina pectoris, hypotension, hypertension, increased cardiac output, tachycardia, arrhythmias, cardiovascular collapse
GI: vomiting, diarrhea, cramps
GU: menstrual irregularities
Musculoskeletal: accelerated bone maturation (in children), decreased bone density (with long-term use in women)
Skin: alopecia (in children), diaphoresis
Other: weight loss, heat intolerance
Drug-drug. Aminoglutethimide, amiodarone, anabolic steroids, antithyroid drugs, asparaginase, barbiturates, carbamazepine, chloral hydrate, cholestyramine, clofibrate, colestipol, corticosteroids, danazol, diazepam, estrogens, ethionamide, fluorouracil, heparin (with I.V. use), insulin, lithium, methadone, mitotane, nitroprusside, oxyphenbutazone, P-aminosalicyclic acid, perphenazine, phenylbutazone, phenytoin, propranolol, salicylates (large doses), sulfonylureas, thiazides: altered thyroid function test results
Anticoagulants: increased anticoagulant action
Beta-adrenergic blockers (selected): decreased beta blocker action
Cardiac glycosides: decreased cardiac glycoside blood level
Cholestyramine, colestipol: liotrix inefficacy
Theophyllines: decreased theophylline clearance
Drug-diagnostic tests. Thyroid function tests: decreased values
Drug-food. Foods high in iron or fiber, soybeans: decreased drug absorption
• Monitor for evidence of overdose, such as signs and symptoms of hyperthyroidism (weight loss, cardiac symptoms, abdominal cramps).
• Watch closely for signs and symptoms of undertreatment.
• In patients with Addison's disease or diabetes mellitus, assess for signs that these conditions are worsening. In diabetic patients, monitor blood glucose level.
• Check vital signs and ECG routinely.
• Monitor thyroid and liver function tests.
• Assess for signs and symptoms of bleeding tendency, especially if patient's taking anticoagulants.
• Inform patient or parents that drug should be taken in morning with or without food.
• Explain that patient may require lifelong therapy and will need to undergo regular blood testing.
• Advise diabetic patient (or his parents) to monitor patient's blood glucose level closely.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• Inform parents that hair loss may occur in children during first few months of therapy but that this effect is usually transient.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and foods mentioned above.