Thyroid, desiccated (USP Thyroid)

Today's med: USP Thyroid, Levothyroxin, Tetraiodothyronine and Triiodothyronine, Thyroid extract   (brand names:Armour, Nature-Throid, Westhroid)

Other Drugs in this class: Levothyroxine sodium,Levothyroxine/Liothyronine

Indications: Replacement or supplemental therapy in hypothyroidism; pituitary TSH suppressants (thyroid nodules, thyroiditis, multinodular goiter, thyroid cancer)

Contraindications: Hypersensitivity to beef or pork or any component of the formulation; untreated thyrotoxicosis; uncorrected adrenal insufficiency

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

Adverse Effects: Adverse reactions often indicative of excess thyroid replacement and/or hyperthyroidism.

<1% (Limited to important or life-threatening): Alopecia, cardiac arrhythmia, chest pain, dyspnea, excessive bone loss with overtreatment (excess thyroid replacement), hand tremor, myalgia, palpitation, tachycardia, tremor

Warnings/Precautions: 

Disease-related concerns:

• Adrenal insufficiency: Use with caution in patients with adrenal insufficiency; symptoms may be exaggerated or aggravated; contraindicated in patients with uncorrected adrenal insufficiency.

• Cardiovascular disease: Use with caution and reduce dosage in patients with angina pectoris or other cardiovascular disease; chronic hypothyroidism predisposes patients to coronary artery disease.

• Diabetes: Use with caution in patients with diabetes mellitus and insipidus; symptoms may be exaggerated or aggravated.

• Myxedema: Use with caution in patients with myxedema; symptoms may be exaggerated or aggravated; initial dosage reduction is recommended in patients with long-standing myxedema.

Special populations:

• Elderly: Avoid use in this age group due to risk of cardiac effects and the availability of safer alternatives (Beers Criteria).

Dosage form specific issues:

• 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.

Other warnings/precautions:

• Infertility (unapproved use): Thyroid supplements are not recommended for the treatment of female or male infertility, unless associated with hypothyroidism.

• Weight reduction (unapproved use): [U.S. Boxed Warning]: In euthyroid patients, thyroid supplements are ineffective and potentially toxic for weight reduction. High doses may produce serious or even life-threatening toxic effects particularly when used with some anorectic drugs.

Monitoring Parameters

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.

Pregnancy Risk Factor

A

Standard Dosing: Oral: Note: The American Association of Clinical Endocrinologists does not recommend the use of desiccated thyroid for thyroid replacement therapy for hypothyroidism (Baskin, 2002).

Children: See table.

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

Table has been converted to the following text.

Recommended Pediatric Dosage for Congenital Hypothyroidism

• 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 2-3 weeks; use 15 mg in patients with cardiovascular disease or long-standing myxedema. Maintenance dose: Usually 60-120 mg/day; monitor TSH and clinical symptoms.

Administration

Administer on an empty stomach. Take in the morning before breakfast.

Dietary Considerations

Should be taken on an empty stomach.

Drug interactions: Bile Acid Sequestrants: May decrease the serum concentration of Thyroid Products. Management: Administer oral thyroid products at least 4 h prior to colesevelam, and at least 1 h before or 4-6 h after cholestyramine. Specific recommendations for colestipol are not available. Monitor for decreased concentrations/effects of the thyroid product.Consider therapy modification

Calcium Polystyrene Sulfonate: May decrease the serum concentration of Thyroid Products. Management: To minimize risk of interaction, separate dosing of oral calcium polystyrene sulfonate and thyroid products (eg, levothyroxine) or administer calcium polystyrene sulfonate rectally. Monitor for signs/symptoms of hypothyroidism with concomitant use (oral). Consider therapy modification

Calcium Salts: May diminish the therapeutic effect of Thyroid Products. Management: Separate the doses of the thyroid product and the oral calcium supplement by at least 4 hours. Consider therapy modification

CarBAMazepine: May decrease the serum concentration of Thyroid Products. Monitor therapy

Estrogen Derivatives: May diminish the therapeutic effect of Thyroid Products. Monitor therapy

Fosphenytoin: May decrease the serum concentration of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Monitor therapy

Lanthanum: May decrease the serum concentration of Thyroid Products. Management: Administer oral thyroid products at least two hours before or after lanthanum. Consider therapy modification

Phenytoin: May decrease the serum concentration of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Monitor therapy

Rifampin: May decrease the serum concentration of Thyroid Products. Monitor therapy

Sodium Iodide I131: Thyroid Products may diminish the therapeutic effect of Sodium Iodide I131. Avoid combination

Sodium Polystyrene Sulfonate: May decrease the serum concentration of Thyroid Products. Management: To minimize risk of interaction, separate dosing of oral sodium polystyrene sulfonate and thyroid products (e.g., levothyroxine) or administer sodium polystyrene sulfonate rectally. Monitor for signs/symptoms of hypothyroidism with concomitant use (oral). Consider therapy modification

Theophylline Derivatives: Thyroid Products may increase the metabolism of Theophylline Derivatives. Exceptions:Dyphylline. Monitor therapy

Vitamin K Antagonists (eg, warfarin): Thyroid Products may enhance the anticoagulant effect of Vitamin K Antagonists.Monitor therapy