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|Thyroid, Desiccated

Thyroid, Desiccated

Trade Names:
Armour Thyroid
- Tablets 15 mg (¼ grain)
- Tablets 30 mg (½ grain)
- Tablets 60 mg (1 grain)
- Tablets 90 mg (1½ grain)
- Tablets 120 mg (2 grain)
- Tablets 180 mg (3 grain)
- Tablets 240 mg (4 grain)
- Tablets 300 mg (5 grain)

Trade Names:
S-P-T
- Capsules 60 mg (1 grain) (Pork thyroid suspended in soybean oil)
- Capsules 120 mg (2 grain) (Pork thyroid suspended in soybean oil)
- Capsules 180 mg (3 grain) (Pork thyroid suspended in soybean oil)
- Capsules 300 mg (5 grain) (Pork thyroid suspended in soybean oil)

Trade Names:
Thyrar
- Tablets 30 mg (½ grain) (Bovine thyroid)
- Tablets 60 mg (1 grain) (Bovine thyroid)
- Tablets 120 mg (2 grain) (Bovine thyroid)

Trade Names:
Thyroid Strong
- Tablets 30 mg (½ grain) (50% stronger than thyroid USP. Each grain is eq. to 1½ grain of thyroid USP.)
- Tablets 60 mg (1 grain) (50% stronger than thyroid USP. Each grain is eq. to 1½ grain of thyroid USP.)
- Tablets 120 mg (2 grain) (50% stronger than thyroid USP. Each grain is eq. to 1½ grain of thyroid USP.)
- Tablets 180 mg (3 grain) (50% stronger than thyroid USP. Each grain is eq. to 1½ grain of thyroid USP.)

Mechanism of Action

Pharmacology

Increases metabolic rate of body tissues.

Pharmacokinetics

Absorption

Levothyroxine (T ₄ ) is only partially absorbed from the GI tract. Absorption varies from 48% to 79%. Fasting increases absorption. Liothyronine (T ₃ ) is almost totally absorbed (95%) in 4 hr.

Distribution

More than 99% is bound to serum proteins.

Metabolism

Deiodination of levothyroxine (T ₄ ) occurs at a number of sites, including liver, kidney, and other tissues.

Indications and Usage

Replacement or supplemental therapy in hypothyroidism; TSH suppression (in thyroid cancer, nodules, goiters, and enlargement in chronic thyroiditis); diagnostic agent to differentiate suspected hyperthyroidism from euthyroidism.

Contraindications

Hypersensitivity to any ingredient; acute MI and thyrotoxicosis uncomplicated by hypothyroidism. Also contraindicated when hypothyroidism and hypoadrenalism (Addison disease) coexist, unless treatment of hypoadrenalism with adrenocortical steroids precedes initiation of thyroid therapy.

Dosage and Administration

Optimal dosage determined by clinical response and laboratory findings.

PO 30 mg/day initially, increasing by 15 mg increments q 2 to 3 wk. In patients with long-standing myxedema, 15 mg/day, particularly if cardiovascular impairment is suspected. Reduce dosage if angina occurs.

60 to 120 mg/day.

PO See table for recommended dose in congenital hypothyroidism.

Larger doses required.

Storage/Stability

Store at room temperature in tightly closed container.

Drug Interactions

Anticoagulant effects may be increased.

May decrease thyroid efficacy.

Digitalis levels may increase, resulting in toxicity.

Theophylline clearance may be altered in hyperthyroid or hypothyroid patients.

Laboratory Test Interactions

Consider changes in thyroid-binding globulin concentration when interpreting T ₄ and T ₃ values. Medicinal or dietary iodine interferes with all in vivo tests of radioiodine uptake, producing low uptakes that may not reflect true decrease in hormone synthesis.

Adverse Reactions

Cardiovascular

Palpitations; tachycardia; cardiac arrhythmias; angina pectoris; cardiac arrest.

CNS

Tremors; headache; nervousness; insomnia.

GI

Diarrhea; vomiting.

Genitourinary

Menstrual irregularities.

Miscellaneous

Hypersensitivity; weight loss; sweating; heat intolerance; fever.

Adverse reactions generally indicate hyperthyroidism caused by therapeutic overdosage.

Precautions

Pregnancy

Category A .

Lactation

Excreted in breast milk.

Children

Routine determinations of serum T ₄ or TSH are strongly advised in newborns. Initiate treatment immediately on diagnosis and continue for life, unless transient hypothyroidism is suspected. In infants, excessive doses of thyroid hormone preparations may produce craniosynostosis. Children may experience transient partial hair loss in first few months of thyroid therapy.

Cardiovascular disease

Use caution when integrity of CV system, particularly coronary arteries is suspect (eg, angina, elderly). Development of chest pain or worsening CV disease requires decrease in dosage. Observe patients with coronary artery disease during surgery, since possibility of cardiac arrhythmias may be greater in those treated with thyroid hormones.

Endocrine disorders

Therapy in patients with concomitant diabetes mellitus or insipidus or adrenal insufficiency (Addison disease) exacerbates intensity of symptoms. Therapy of myxedema coma requires simultaneous administration of glucocorticoids. In patients whose hypothyroidism is secondary to hypopituitarism, adrenal insufficiency, if present, should be corrected with corticosteroids before administering thyroid hormones.

Hyperthyroid effects

May rarely precipitate hyperthyroid state or may aggravate existing hyperthyroidism.

Morphologic hypogonadism and nephrosis

Rule out before therapy.

Myxedema

Patients are particularly sensitive to thyroid preparations. Begin with small doses.

Obesity

Should not be used for weight reduction; may produce serious or even life-threatening toxicity in larger doses, particularly when given with anorexiants.

Overdosage

Symptoms

Tachycardia, arrhythmias, hypertension, angina, fever, tremor, vomiting, diarrhea, insomnia, headache, seizures, coma.

Patient Information

• Explain that children may have short-term temporary hair loss at start of therapy.
• Tell patient to report fever, weight loss, menstrual irregularity, palpitations, chest pain, headache, faint feeling, sweatiness, diarrhea, vomiting, inability to sleep, excitability, irritability, anxiety, nervousness, or any changes to health care provider.
• Teach patient to avoid OTC preparations and food with iodine: iodinated salt, soy beans, tofu, turnips, some seafood, some types of bread.
• Instruct patient not to switch drug brands unless health care provider approves.
• Caution patients not to take thyroid for weight control.