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Pronunciation:

(THYE roid)

U.S. Brand Names:

Armour® Thyroid; Nature-Throid® NT; Westhroid®

Synonyms:

Desiccated Thyroid; Thyroid Extract; Thyroid USP

Generic Available:

Yes

Use:

Replacement or supplemental therapy in hypothyroidism; pituitary TSH suppressants (thyroid nodules, thyroiditis, multinodular goiter, thyroid cancer), thyrotoxicosis, diagnostic suppression tests

Pregnancy Risk Factor:

Lactation:

Enters breast milk/compatible

Contraindications:

Hypersensitivity to beef or pork or any component of the formulation; recent myocardial infarction; thyrotoxicosis uncomplicated by hypothyroidism; uncorrected adrenal insufficiency

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. Chronic hypothyroidism predisposes patients to coronary artery disease. Desiccated thyroid contains variable amounts of T3, T4, and other triiodothyronine compounds which are more likely to cause cardiac signs or symptoms due to fluctuating levels. Should avoid use in the elderly for this reason. Drug of choice is levothyroxine in the minds of many clinicians.

Adverse Reactions:

<1%: Abdominal cramps, alopecia, ataxia, cardiac arrhythmia, changes in menstrual cycle, chest pain, constipation, diaphoresis, diarrhea, dyspnea, excessive bone loss with overtreatment (excess thyroid replacement), fever, hand tremor, headache, heat intolerance, increased appetite, insomnia, myalgia, nervousness, palpitation, tachycardia, tremor, vomiting, weight loss

Overdosage/Toxicology:

Chronic excessive use results in signs and symptoms of hyperthyroidism, weight loss, nervousness, sweating, tachycardia, insomnia, heat intolerance, palpitations, vomiting, psychosis, fever, seizures, angina, arrhythmias, and CHF in those predisposed.

Reduce dose or temporarily discontinue therapy. 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 and give general supportive care.

Drug Interactions:

Decreased effect:

Beta-blocker effect is decreased when patients become euthyroid

Thyroid hormones increase the therapeutic need for oral hypoglycemics or insulin

Estrogens increase TBG, thereby decreasing effect of thyroid replacement

Cholestyramine and colestipol decrease the effect of orally administered thyroid replacement

Serum digitalis concentrations are reduced in hyperthyroidism or when hypothyroid patients are converted to a euthyroid state

Theophylline levels decrease when hypothyroid patients converted to a euthyroid state

Increased toxicity: Thyroid may potentiate the hypoprothrombinemic effect of oral anticoagulants

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; 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: T4: 48% to 79%; T3: 95%; desiccated thyroid contains thyroxine, liothyronine, and iodine (primarily bound)

Metabolism: Thyroxine: Largely converted to liothyronine

Half-life elimination, serum: Liothyronine: 1-2 days; Thyroxine: 6-7 days

Dosage:

Oral:

Children: See table.

Dietary Considerations:

Recommended Pediatric Dosage for Congenital Hypothyroidism

Age	Daily Dose (mg)	Daily Dose/kg (mg)
0-6 mo	15-30	4.8-6
6-12 mo	30-45	3.6-4.8
1-5 y	45-60	3-3.6
6-12 y	60-90	2.4-3
>12 y	>90	1.2-1.8

Adults: Initial: 15-30 mg; increase with 15 mg increments every 2-4 weeks; use 15 mg in patients with cardiovascular disease or myxedema. Maintenance dose: Usually 60-120 mg/day; monitor TSH and clinical symptoms.

Thyroid cancer: Requires larger amounts than replacement therapy

Dietary Considerations:

Should be taken on an empty stomach.

Patient Education:

Inform prescriber of all prescriptions, OTC medications, or herbal products you are taking, and any allergies you have. Do not take any new medication during therapy unless approved by prescriber. Thyroid replacement therapy is generally for life. Take as directed, in the morning before breakfast. Do not take antacids or iron preparations within 8 hours of thyroid medication. 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). If you have diabetes, monitor glucose levels closely (may increase need for oral hypoglycemics or insulin). Report chest pain, rapid heart rate, palpitations, heat intolerance, excessive sweating, increased nervousness, agitation, or lethargy.

Nursing Implications:

Monitor T4, TSH, heart rate, blood pressure, clinical signs of hypo- and hyperthyroidism; 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. Thyroid replacement requires periodic assessment of thyroid status; 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.

Anesthesia and Critical Care Concerns/Other Considerations:

Equivalent dosing: Thyroid USP 60 mg is equivalent to:

Levothyroxine 0.05-0.06 mg

Liothyronine 15-37.5 mcg

Liotrix 60 mg

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 thyroid preparations

Mental Health: Effects on Mental Status:

May cause nervousness or insomnia

Mental Health: Effects on Psychiatric Treatment:

Use to augment antidepressants and treat lithium-induced hypothyroidism

Dosage Forms:

Capsule: 15 mg, 30 mg, 60 mg, 90 mg, 120 mg, 180 mg, 240 mg

Tablet: 30 mg, 32.5 mg, 60 mg, 65 mg, 120 mg, 130 mg, 180 mg

Armour® Thyroid: 15 mg, 30 mg, 60 mg, 90 mg, 120 mg, 180 mg, 240 mg, 300 mg

Nature-Throid® NT, Westhroid®: 32.4 mg, 64.8 mg, 129.6 mg, 194.4 mg

References

Bhasin S, Wallace W, Lawrence JB, et al, "Sudden Death Associated With Thyroid Hormone Abuse,"Am J Med, 1981, 71(5):887-90.

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.

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.

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.

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