Class: Thyroid hormone
- Tablets 3.1 mcg T 3 /12.5 mcg T 4 (thyroid equivalent to 15)
- Tablets 6.25 mcg T 3 /25 mcg T 4 (thyroid equivalent to 30)
- Tablets 12.5 mcg T 3 /50 mcg T 4 (thyroid equivalent to 60)
- Tablets 25 mcg T 3 /100 mcg T 4 (thyroid equivalent to 120)
- Tablets 37.5 mcg T 3 /150 mcg T 4 (thyroid equivalent to 180)
Increases metabolic rate of body tissues; is needed for normal growth and maturation.
40% to 80% of T 4 is absorbed; absorption is increased by fasting and decreased by certain foods. Approximately 95% of T 3 is absorbed in 4 h.
More than 99% is bound to serum proteins. Minimal amounts excreted in breast milk.
Approximately 80% of T 3 comes from monodeiodination of T 4 . Conjugated hormone is found in the bile and gut where it may undergo enterohepatic circulation.
Primarily eliminated by the kidneys. Approximately 20% of T 4 is excreted in feces.
T 4 absorption and urinary excretion are decreased with age.
Indications and Usage
Replacement or supplemental therapy in hypothyroidism; pituitary TSH suppression in treatment or prevention of various types of euthyroid goiters, including thyroid nodules, subacute or chronic lymphocytic thyroiditis (Hashimoto's), multinodular goiter, and management of thyroid cancer; diagnostic agent in suppression tests to differentiate suspected and hyperthyroidism or thyroid gland autonomy.
Diagnosed but uncorrected adrenal cortical insufficiency; untreated thyrotoxicosis; apparent hypersensitivity to any component of the product.
Dosage and AdministrationHypothyroidism
PO Start with low doses, with increments depending on the CV status. Usual starting dose is 1 tablet of Thyrolar ½ with increments of 1 tablet of Thyrolar ¼ every 2 to 3 wk. In patients with long-standing myxedema, the recommended starting dose is 1 tablet daily of Thyrolar ¼ and reduce dosage if angina occurs. Readjust dosage within first 4 wk of therapy after proper clinical and laboratory evaluations, including serum levels of T 4 (bound and free) and TSH.Congenital Hypothyroidism
Children (older than 12 yr of age)
PO More than 18.75 mcg of T 3 and 75 mcg T 4 daily.Children (6 to 12 yr of age)
PO 12.5 mcg of T 3 and 50 mcg T 4 to 18.75 mcg of T 3 and 75 mcg T 4 daily.Children (1 to 5 yr of age)
PO 9.35 mcg of T 3 and 37.5 mcg of T 4 to12.5 mcg of T 3 and 50 mcg T 4 daily.Children (6 mo to 12 mo)
PO 6.25 mcg of T 3 and 25 mcg of T 4 to 9.35 mcg of T 3 and 37.5 mcg of T 4 daily.Children (0 mo to 6 mo)
PO 3.1 mcg of T 3 and 12.5 mcg of T 4 to 6.25 mcg of T 3 and 25 mcg of T 4 daily.Thyroid Cancer
PO Larger amounts of thyroid hormone than those used for replacement therapy are required.Diagnostic Agent
PO Usual suppressive dose of T 4 is 1.56 mcg/kg/day for 7 to 10 days.
Administer prescribed dose once daily. When given on an empty stomach, absorption is increased. However, to maintain steady blood levels and effect, be consistent in administering drug with or without food.
Store tablets in refrigerator (36° to 46°F).
May increase anticoagulant effect.Cholestyramine, colestipol
Bind T 3 and T 4 in the intestine, impairing absorption.Estrogens, oral contraceptives
Thyroid requirement may be increased in patients with nonfunctioning thyroid gland or receiving thyroid replacement therapy.Insulin, oral hypoglycemics
Requirements of these agents may be increased by liotrix.
Laboratory Test Interactions
Consider changes in thyroid binding globulin concentration when interpreting thyroxine (T 4 ) and triiodothyronine (T 3 ) values; medicinal or dietary iodine interferes with all in vivo tests of radioiodine uptake, producing low uptakes that may not reflect true decrease in hormone synthesis.
Hypermetabolic state (indicative of hyperthyroidism).
Monitor blood sugar in diabetic patient when drug is started or dose is changed.Development baseline tests
Monitor height, weight, and intellectual function in children to document normal development.Thyroid function tests
Ensure that thyroid function tests (eg, TSH, T 4 ) are determined prior to starting therapy and periodically during treatment.
Category A .
Minimal amounts excreted in breast milk.
When used for congenital hypothyroidism, routine determinations of serum T 4 or TSH are strongly advised in newborns.
Special Risk Patients
Use with great caution in patients with CV disease, especially if integrity of coronary arteries is suspected, including patients with angina pectoris or the elderly; may aggravate intensity of symptoms in patients with diabetes mellitus or insipidus or adrenal cortical insufficiency.
Requires simultaneous administration of glucocorticoids.
Should not be used for weight reduction; may produce serious or life-threatening toxicity particularly when given with sympathomimetics or anorexiants.
- Instruct patient to take prescribed dose once daily.
- Advise patient to take each dose at about the same time each day and consistently with or without food.
- Advise patient that therapy will be started with a low dose and that the dose may be gradually increased until max benefit is obtained.
- Caution patient not to change the dose or stop taking unless advised to do so by health care provider.
- Inform patient that drug controls, but does not cure, symptoms of hypothyroidism, and to continue taking the drug as prescribed even when feeling better.
- Advise patient that thyroid replacement therapy is usually a life-long therapy.
- Advise patient to notify health care provider if any of the following are noted: chest pain, increased heart rate, palpitations, excessive sweating, heat intolerance, nervousness, tremors, other unusual events.
- Instruct diabetic patient to monitor blood glucose more frequently when drug is started or dose is changed and to inform health care provider of significant changes in readings.
- Explain to parent or guardian that partial hair loss may be experienced by child in first few months of therapy but that this adverse reaction is usually reversible.
Copyright © 2009 Wolters Kluwer Health.