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Pronunciation |
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(THYE
royd) |
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U.S. Brand
Names |
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Armour® Thyroid; S-P-T; Thyrar®;
Thyroid
Strong® |
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Generic
Available |
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Yes |
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Synonyms |
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Desiccated Thyroid; Thyroid Extract; Thyroid USP |
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Pharmacological Index |
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Thyroid Product |
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Use |
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Replacement or supplemental therapy in hypothyroidism; pituitary TSH
suppressants (thyroid nodules, thyroiditis, multinodular goiter, thyroid
cancer), thyrotoxicosis, diagnostic suppression tests |
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Pregnancy Risk
Factor |
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A |
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Contraindications |
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Recent myocardial infarction or thyrotoxicosis uncomplicated by
hypothyroidism uncorrected adrenal insufficiency; hypersensitivity to beef or
pork or any constituent |
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Warnings/Precautions |
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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. |
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Adverse
Reactions |
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<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 |
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Overdosage/Toxicology |
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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. |
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Drug
Interactions |
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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 |
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Mechanism of
Action |
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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 |
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Pharmacodynamics/Kinetics |
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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 |
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Usual Dosage |
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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
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Dietary
Considerations |
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Should be administered on an empty stomach |
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Mental Health: Effects
on Mental Status |
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May cause nervousness or insomnia |
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Mental Health:
Effects on Psychiatric
Treatment |
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Use to augment antidepressants and treat lithium-induced
hypothyroidism |
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Dental Health: Local
Anesthetic/Vasoconstrictor
Precautions |
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No precautions with vasoconstrictor are necessary if patient is well
controlled with thyroid preparations |
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Dental Health:
Effects on Dental Treatment |
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No effects or complications reported |
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Patient
Information |
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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. |
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Nursing
Implications |
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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. |
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Dosage Forms |
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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
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References |
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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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