Liotrix

Pronunciation

(LYE oh triks)

U.S. Brand Names

Thyrolar®

Synonyms

T3/T4 Liotrix

Generic Available

Canadian Brand Names

Thyrolar®

Use

Replacement or supplemental therapy in hypothyroidism (uniform mixture of T4:T3 in 4:1 ratio by weight); little advantage to this product exists and cost is not justified

Pregnancy Risk Factor

Pregnancy Implications

Untreated hypothyroidism may have adverse effects on fetal growth and development, and is associated with higher rate of complications; treatment should not be discontinued during pregnancy.

Contraindications

Hypersensitivity to liotrix or any component of the formulation; recent myocardial infarction or thyrotoxicosis, uncomplicated by hypothyroidism; uncorrected adrenal insufficiency, hypersensitivity to active or extraneous constituents

Warnings/Precautions

Ineffective for weight reduction; high doses may produce serious or even life-threatening toxic effects particularly when used with some anorectic drugs; use cautiously in patients with pre-existing cardiovascular disease (angina, CHD), elderly since they may be more likely to have compromised cardiovascular function

Adverse Reactions

Frequency not defined.

Cardiovascular: Palpitations, cardiac arrhythmia, tachycardia, chest pain

Central nervous system: Nervousness, headache, insomnia, fever, ataxia

Dermatologic: Alopecia

Endocrine & metabolic: Changes in menstrual cycle, weight loss, increased appetite

Gastrointestinal: Diarrhea, abdominal cramps, constipation, vomiting

Neuromuscular & skeletal: Myalgia, hand tremor, tremor

Respiratory: Dyspnea

Miscellaneous: Diaphoresis, allergic skin reactions (rare)

Overdosage/Toxicology

Chronic overdose may cause weight loss, nervousness, sweating, tachycardia, insomnia, heat intolerance, menstrual irregularities, palpitations, psychosis, fever; acute overdose may cause fever, hypoglycemia, CHF, unrecognized adrenal insufficiency

Reduce dose or temporarily discontinue therapy; normal hypothalamic-pituitary-thyroid axis will return to normal in 6-8 weeks; serum T4 levels do not correlate well with toxicity

In massive acute ingestion, reduce GI absorption, administer general supportive care; treat congestive heart failure with digitalis glycosides; excessive adrenergic activity (tachycardia) require propranolol 1-3 mg I.V. over 10 minutes or 80-160 mg orally/day; fever may be treated with acetaminophen

Drug Interactions

Aluminum- and magnesium-containing antacids, calcium carbonate, simethicone, or sucralfate: May decrease T4 absorption; separate dose from thyroid hormones by at least 4 hours.

Antidiabetic agents (biguanides, meglitinides, sulfonylureas, thiazolidinediones, insulin): Changes in thyroid function may alter requirements of antidiabetic agent. Monitor closely at initiation of therapy, or when dose is changed or discontinued.

Cholestyramine and colestipol: Decrease T4 absorption; separate dose from thyroid hormones by at least 4 hours.

Digoxin: Digoxin levels may be reduced in hyperthyroidism; therapeutic effect may be reduced. Impact of thyroid replacement should be monitored.

Iron: Decreases T4 absorption; separate dose from thyroid hormones by at least 4 hours

Kayexalate®: Decreases T4 absorption; separate dose from thyroid hormones by at least 4 hours

Ketamine: May cause marked hypertension and tachycardia; monitor

Ritonavir: May alter response to thyroid hormones (limited documentation/case report); monitor

Somatrem, somatropin: Excessive thyroid hormone levels lead to accelerated epiphyseal closure; inadequate replacement interferes with growth response to growth hormone. Effect of thyroid replacement not specifically evaluated; use caution.

SSRI antidepressants: May need to increase dose of thyroid hormones when SSRI is added to a previously stabilized patient.

Sympathomimetics: Effects of sympathomimetic agent or thyroid hormones may be increased. Risk of coronary insufficiency is increased in patients with coronary artery disease when these agents are used together.

Theophylline, caffeine: Decreased theophylline clearance in hypothyroid patients; monitor during thyroid replacement.

Tricyclic and tetracyclic antidepressants: Therapeutic and toxic effects of thyroid hormones and the antidepressant are increased.

Warfarin (and other oral anticoagulants): The hypoprothrombinemic response to warfarin may be altered by a change in thyroid function or replacement. Replacement may dramatically increase response to warfarin. However, initiation of warfarin in a patient stabilized on a dose of thyroid hormones does not appear to require a significantly different approach.

Note: Several medications have effects on thyroid production or conversion. The impact in thyroid replacement has not been specifically evaluated, but patient response should be monitored:

Methimazole: Decreases thyroid hormone secretion, while propylthiouracil decrease thyroid hormone secretion and decreases conversion of T4 to T3.

Beta-adrenergic antagonists: Decrease conversion of T4 to T3 (dose related, propranolol 160 mg/day); patients may be clinically euthyroid.

Iodide, iodine-containing radiographic contrast agents may decrease thyroid hormone secretion; may also increase thyroid hormone secretion, especially in patients with Graves' disease.

Other agents reported to impact on thyroid production/conversion include aminoglutethimide, amiodarone, chloral hydrate, diazepam, ethionamide, interferon-alpha, interleukin-2, lithium, lovastatin (case report), glucocorticoids (dose-related), mercaptopurine, sulfonamides, thiazide diuretics, and tolbutamide.

In addition, a number of medications have been noted to cause transient depression in TSH secretion, which may complicate interpretation of monitoring tests for thyroid hormones, including corticosteroids, octreotide, and dopamine. Metoclopramide may increase TSH secretion.

Stability

Store at 2°C to 8°C (36°F to 46°F); protect from light

Mechanism of Action

The primary active compound is T3 (triiodothyronine), which may be converted from T4 (thyroxine) and then circulates throughout the body to influence growth and maturation of various tissues. Liotrix is uniform mixture of synthetic T4 and T3 in 4:1 ratio; exact mechanism of action is unknown; however, it is believed the thyroid hormone exerts its many metabolic effects through control of DNA transcription and protein synthesis; involved in normal metabolism, growth, and development; promotes gluconeogenesis, increases utilization and mobilization of glycogen stores and stimulates protein synthesis, increases basal metabolic rate

Pharmacodynamics/Kinetics

Absorption: 50% to 95%

Metabolism: Partially hepatic, renal, and in intestines

Half-life elimination: 6-7 days

Time to peak, serum: 12-48 hours

Excretion: Partially feces (as conjugated metabolites)

Dosage

Oral:

Congenital hypothyroidism:

Children (dose of T4 or levothyroxine/day):

0-6 months: 8-10 mcg/kg or 25-50 mcg/day

6-12 months: 6-8 mcg/kg or 50-75 mcg/day

1-5 years: 5-6 mcg/kg or 75-100 mcg/day

6-12 years: 4-5 mcg/kg or 100-150 mcg/day

>12 years: 2-3 mcg/kg or >150 mcg/day

Hypothyroidism (dose of thyroid equivalent):

Adults: 30 mg/day (15 mg/day if cardiovascular impairment), increasing by increments of 15 mg/day at 2- to 3-week intervals to a maximum of 180 mg/day (usual maintenance dose: 60-120 mg/day)

Elderly: Initial: 15 mg, adjust dose at 2- to 4-week intervals by increments of 15 mg

Monitoring Parameters

T4, TSH, heart rate, blood pressure, clinical signs of hypo- and hyperthyroidism; TSH is the most reliable guide for evaluating adequacy of thyroid replacement dosage. TSH may be elevated during the first few months of thyroid replacement despite patients being clinically euthyroid. In cases where T4 remains low and TSH is within normal limits, an evaluation of "free" (unbound) T4 is needed to evaluate further increase in dosage.

Reference Range

TSH: 0.4-10 (for those 80 years) mIU/L

T4: 4-12 mcg/dL (SI: 51-154 nmol/L)

T3 (RIA) (total T3): 80-230 ng/dL (SI: 1.2-3.5 nmol/L)

T4 free (Free T4): 0.7-1.8 ng/dL (SI: 9-23 pmol/L)

Test Interactions

Many drugs may have effects on thyroid function tests; para-aminosalicylic acid, aminoglutethimide, amiodarone, barbiturates, carbamazepine, chloral hydrate, clofibrate, colestipol, corticosteroids, danazol, diazepam, estrogens, ethionamide, fluorouracil, I.V. heparin, insulin, lithium, methadone, methimazole, mitotane, nitroprusside, oxyphenbutazone, phenylbutazone, PTU, perphenazine, phenytoin, propranolol, salicylates, sulfonylureas, and thiazides

Patient Education

Do not change brands without physician's knowledge; report immediately to physician any chest pain, increased pulse, palpitations, heat intolerances, excessive sweating; do not discontinue without notifying your physician; replacement therapy will be for life; take as a single dose before breakfast

Nursing Implications

Monitor T4, TSH, heart rate, blood pressure, clinical signs of hypo- and hyperthyroidism; TSH is the most reliable guide for evaluating adequacy of thyroid replacement dosage. TSH may be elevated during the first few months of thyroid replacement despite patients being clinically euthyroid. In cases where T4 remains low and TSH is within normal limits, an evaluation of "free" (unbound) T4 is needed to evaluate further increase in dosage

Additional Information

Equivalent doses: Thyroid USP 60 mg ~ levothyroxine 0.05-0.06 mg ~ liothyronine 0.015-0.0375 mg

50-60 mg thyroid ~50-60 mcg levothyroxine and 12.5-15 mcg liothyronine. Since T3 is produced by monodeiodination of T4 in peripheral tissues (80%) and since elderly have decreased T3 (25% to 40%), little advantage to this product exists and cost is not justified; no advantage over synthetic levothyroxine sodium.

Anesthesia and Critical Care Concerns/Other Considerations

Since T3 is produced by monodeiodination of T4 in peripheral tissues (80%) and since elderly have decreased T3 (25% to 40%), little advantage to this product exists and cost is not justified. Its use has no advantage over synthetic levothyroxine sodium.

Equivalent dosing: 1 grain (60 mg) liotrix is equivalent to:

0.05-0.06 mg levothyroxine

60 mg thyroid USP

12.5-15 mcg T3

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No precautions with vasoconstrictor are necessary if patient is well controlled with liotrix

Mental Health: Effects on Mental Status

May cause nervousness or insomnia

Mental Health: Effects on Psychiatric Treatment

None reported

Dosage Forms

Tablet:

¹ /4 [levothyroxine sodium 12.5 mcg and liothyronine sodium 3.1 mcg]

¹ /2 [levothyroxine sodium 25 mcg and liothyronine sodium 6.25 mcg]

1 [levothyroxine sodium 50 mcg and liothyronine sodium 12.5 mcg]

2 [levothyroxine sodium 100 mcg and liothyronine sodium 25 mcg]

3 [levothyroxine sodium 150 mcg and liothyronine sodium 37.5 mcg]

References

Berkner PD, Starkman H, and Person N, "Acute L-Thyroxine Overdose: Therapy With Sodium Ipodate: Evaluation of Clinical and Physiologic Parameters," J Emerg Med , 1991, 9(3):129-31.

Binimelis J, Bassas L, Marruecos L, et al, "Massive Thyroxine Intoxication: Evaluation of Plasma Extraction," Intens Care Med , 1987, 13(1):33-8.

Gorman RL, Chamberlain JM, Rose SR, et al, "Massive Levothyroxine Overdose: High Anxiety - Low Toxicity," Pediatrics , 1988, 82(4):666-9.

Helfand M and Crapo LM, "Monitoring Therapy in Patients Taking Levothyroxine," Ann Intern Med , 1990, 113(6):450-4.

Johnson DG and Campbell S, "Hormonal and Metabolic Agents," Geriatric Pharmacology , Bressler R and Katz MD, eds, New York, NY: McGraw-Hill, 1993, 427-50.

Kulig K, Golightly LK, and Rumack BH, "Levothyroxine Overdose Associated With Seizures in a Young Child," JAMA , 1985, 254(15):2109-10.

Mandel SH, Magnusson AR, Burton BT, et al, "Massive Levothyroxine Ingestion: Conservative Management," Clin Pediatr (Phila) , 1989, 28(8):374-6.

Sanders LR, "Pituitary, Thyroid, Adrenal and Parathyroid Diseases in the Elderly," Geriatric Medicine , 1990, 475-87.

Sawin CT, Geller A, Hershman JM, et al, "The Aging Thyroid. The Use of Thyroid Hormone in Older Persons," JAMA , 1989, 261(18):2653-5.

Watts NB, "Use of a Sensitive Thyrotropin Assay for Monitoring Treatment With Levothyroxine," Arch Intern Med , 1989, 149(2):309-12.

International Brand Names

Thyrolar® (CA)

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