Yes

Thyroid Product

Replacement or supplemental therapy in hypothyroidism; some clinicians suggest levothyroxine is the drug of choice for replacement therapy

A

Recent myocardial infarction or thyrotoxicosis, uncorrected adrenal insufficiency, hypersensitivity to levothyroxine sodium or any component

Ineffective for weight reduction; high doses may produce serious or even life-threatening toxic effects particularly when used with some anorectic drugs. Use with caution and reduce dosage in patients with angina pectoris or other cardiovascular disease; levothyroxine tablets contain tartrazine dye which may cause allergic reactions in susceptible individuals; use cautiously in elderly since they may be more likely to have compromised cardiovascular functions. Patients with adrenal insufficiency, myxedema, diabetes mellitus and insipidus may have symptoms exaggerated or aggravated; thyroid replacement requires periodic assessment of thyroid status. Chronic hypothyroidism predisposes patients to coronary artery disease.

<1%: Palpitations, cardiac arrhythmias, tachycardia, chest pain, nervousness, headache, insomnia, fever, ataxia, alopecia, changes in menstrual cycle, weight loss, increased appetite, diarrhea, abdominal cramps, constipation, myalgia, hand tremors, tremor, shortness of breath, diaphoresis

Chronic overdose is treated by withdrawal of the drug; massive overdose may require beta-blockers for increased sympathomimetic activity. Chronic overdose may cause hyperthyroidism, 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.

Decreased effect:

Phenytoin may decrease levothyroxine levels

Cholestyramine may decrease absorption of levothyroxine

Increased oral hypoglycemic requirements

Increased effect: Increased effects of oral anticoagulants

Increased toxicity: Tricyclic antidepressants may increase toxic potential of both drugs

Protect tablets from light; do not mix I.V. solution with other I.V. infusion solutions; reconstituted solutions should be used immediately and any unused portions discarded

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

Onset of therapeutic effect: Oral: 3-5 days; I.V. Within 6-8 hours

Peak effect: I.V.: Within 24 hours

Absorption: Oral: Erratic

Metabolism: In the liver to triiodothyronine (active)

Time to peak serum concentration: 2-4 hours

Half-life: Euthyroid: 6-7 days; Hypothyroid: 9-10 days; Hyperthyroid: 3-4 days

Elimination: In feces and urine

Children: Congenital hypothyroidism:

Oral:

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

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

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

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

>12 years: 2-3 mcg/kg/day or greater than or equal to 150 mcg/day

I.M., I.V.: 50% to 75% of the oral dose

Adults:

Oral: Initial: 0.05 mg/day, then increase by increments of 25 mcg/day at intervals of 2-3 weeks; average adult dose: 100-200 mcg/day; maximum dose: 200 mcg/day

I.M., I.V.: 50% of the oral dose

Myxedema coma or stupor: I.V.: 200-500 mcg one time, then 100-300 mcg the next day if necessary

Thyroid suppression therapy: Oral: 2-6 mcg/kg/day for 7-10 days

Should be administered on an empty stomach; limit intake of goitrogenic foods (asparagus, cabbage, peas, turnip greens, broccoli, spinach, Brussels sprouts, lettuce, soybeans)

Thyroid function test (serum thyroxine, thyrotropin concentrations), resin triiodothyronine uptake (RT₃U), free thyroxine index (FTI), 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

Pediatrics: Cord T₄ and values in the first few weeks are much higher, falling over the first months and years. greater than or equal to 10 years: ~5.8-11 mg/dL (SI: 75-142 nmol/L). Borderline low: less than or equal to 4.5-5.7 mg/dL (SI: 58-73 nmol/L); low: less than or equal to 4.4 mg/dL (SI: 57 nmol/L); results <2.5 mg/dL (SI: <32 nmol/L) are strong evidence for hypothyroidism.

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

May rarely cause nervousness or insomnia

Used to augment antidepressants; TCAs may increase toxic potential of both drugs

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

No effects or complications reported

Thyroid replacement therapy is generally for life. Take as directed, in the morning before breakfast. Do not change brands and do not discontinue without consulting prescriber. Consult prescriber if drastically increasing or decreasing intake of goitrogenic food (eg, asparagus, cabbage, peas, turnip greens, broccoli, spinach, Brussels sprouts, lettuce, soybeans). Report chest pain, rapid heart rate, palpitations, heat intolerance, excessive sweating, increased nervousness, agitation, or lethargy.

I.V. form must be prepared immediately prior to administration; should not be admixed with other solutions

Powder for injection, as sodium, lyophilized: 200 mcg/vial (6 mL, 10 mL); 500 mcg/vial (6 mL, 10 mL)

Tablet, as sodium: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg

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.

Escalante DA, Arem N, and Arem R, "Assessment of Interchangeability of Two Brands of Levothyroxine Preparations With a Third-Generation TSH Assay," Am J Med, 1995, 98(4):374-8.

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.

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.

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.

Tunget CL, Clark RF, Turchen SG, et al, "Raising the Decontamination Level for Thyroid Hormone Ingestions," Am J Emerg Med, 1995, 13(1):9-13.

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