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Thyroid
Pronunciation
U.S. Brand Names
Generic Available
Synonyms
Pharmacological Index
Use
Pregnancy Risk Factor
Contraindications
Warnings/Precautions
Adverse Reactions
Overdosage/Toxicology
Drug Interactions
Mechanism of Action
Pharmacodynamics/Kinetics
Usual Dosage
Dietary Considerations
Mental Health: Effects on Mental Status
Mental Health: Effects on Psychiatric Treatment
Dental Health: Local Anesthetic/Vasoconstrictor Precautions
Dental Health: Effects on Dental Treatment
Patient Information
Nursing Implications
Dosage Forms
References

Pronunciation
(THYE royd)

U.S. Brand Names
Armour® Thyroid; S-P-T; Thyrar®; Thyroid Strong®

Generic Available

Yes


Synonyms
Desiccated Thyroid; Thyroid Extract; Thyroid USP

Pharmacological Index

Thyroid Product


Use

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


Pregnancy Risk Factor

A


Contraindications

Recent myocardial infarction or thyrotoxicosis uncomplicated by hypothyroidism uncorrected adrenal insufficiency; hypersensitivity to beef or pork or any constituent


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%:

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

Dermatologic: Alopecia

Endocrine & metabolic: Changes in menstrual cycle

Gastrointestinal: Weight loss, increased appetite, diarrhea, abdominal cramps, vomiting, constipation

Neuromuscular & skeletal: Excessive bone loss with overtreatment (excess thyroid replacement), tremor, hand tremors, myalgia

Respiratory: Shortness of breath

Miscellaneous: Heat intolerance, diaphoresis


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.


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 is 48% to 79% absorbed; T3 is 95% absorbed; desiccated thyroid contains thyroxine, liothyronine, and iodine (primarily bound); following absorption thyroxine is largely converted to liothyronine

Serum half-life:

Liothyronine: 1-2 days

Thyroxine: 6-7 days


Usual Dosage

Oral:

0-6 months: 15-30 mg/day; 4.8-6 mg/kg/day

6-12 months: 30-45 mg/day; 3.6-4.8 mg/kg/day

1-5 years: 45-60 mg/day; 3-3.6 mg/kg/day

6-12 years: 60-90 mg/day; 2.4-3 mg/kg/day

>12 years: >90 mg/day; 1.2-1.8 mg/kg/day

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 administered on an empty stomach


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


Dental Health: Local Anesthetic/Vasoconstrictor Precautions

No precautions with vasoconstrictor are necessary if patient is well controlled with thyroid preparations


Dental Health: Effects on Dental Treatment

No effects or complications reported


Patient Information

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.


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.


Dosage Forms

Capsule, pork source in soybean oil (S-P-T): 60 mg, 120 mg, 180 mg, 300 mg

Tablet:

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

Thyrar® (bovine source): 30 mg, 60 mg, 120 mg

Thyroid Strong® (60 mg is equivalent to 90 mg thyroid USP):

Regular: 30 mg, 60 mg, 120 mg

Sugar coated: 30 mg, 60 mg, 120 mg, 180 mg

Thyroid USP: 15 mg, 30 mg, 60 mg, 120 mg, 180 mg, 300 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.

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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