Thyroid tablets

Armour Thyroid tablets (thyroid tablets, USP) are supplied as follows: 15 mg (1/4 gr) are available in bottles of 100 (NDC 0456-0457-01). 30 mg (½ gr) are available in bottles of 100 (NDC 0456-0458- 01) and unit dose cartons of 100 (NDC 0456-0458-63). 60 mg (1 gr) are available in bottles of 100 (NDC 0456-0459-01) and unit dose cartons of 100 (NDC 0456-0459-63). 90 mg (1 ½ gr) are available in bottles of 100 (NDC 0456-0460-01). 120 mg (2 gr) are available in bottles of 100 (NDC 0456-0461-01) and unit dose cartons of 100 (NDC 0456-0461-63). 180 mg (3 gr) are available in bottles of 100 (NDC 0456-0462-01). 240 mg (4 gr) are available in bottles of 100 (NDC 0456-0463- 01). 300 mg (5 gr) are available in bottles of 100 (NDC 0456-0464-01). The bottles of 100 are special dispensing bottles with child-resistant closures.

Armour Thyroid tablets are evenly colored, light tan, round tablets, with convex surfaces. One side is debossed with a mortar and pestle beneath the letter “A” on the top and strength code letters on the bottom as defined below

Note: (T3 liothyronine is approximately four times as potent as T4 levothyroxine on a microgram for microgram basis.)

Store in a tight container protected from light and moisture. Store between 15°C and 30°C (59°F and 86°F).

*Armour Thyroid (thyroid tablets, USP) has not been approved by FDA as a new drug.

Forest Pharmaceuticals, Inc., A Subsidiary of Forest Laboratories, Inc., St. Louis, MO 63045. Revised: Jan 2011

The steps in the synthesis of the thyroid hormones are controlled by thyrotropin (Thyroid Stimulating Hormone, TSH) secreted by the anterior pituitary. This hormone's secretion is in turn controlled by a feedback mechanism effected by the thyroid hormones themselves and by thyrotropin releasing hormone (TRH), a tripeptide of hypothalamic origin. Endogenous thyroid hormone secretion is suppressed when exogenous thyroid hormones are administered to euthyroid individuals in excess of the normal gland's secretion.

The mechanisms by which thyroid hormones exert their physiologic action are not well understood. These hormones enhance oxygen consumption by most tissues of the body, increase the basal metabolic rate, and the metabolism of carbohydrates, lipids, and proteins. Thus, they exert a profound influence on every organ system in the body and are of particular importance in the development of the central nervous system.

The normal thyroid gland contains approximately 200 mcg of levothyroxine (T4) per gram of gland, and 15 mcg of liothyronine (T3) per gram. The ratio of these two hormones in the circulation does not represent the ratio in the thyroid gland, since about 80 percent of peripheral liothyronine (T3) comes from monodeiodination of levothyroxine (T4). Peripheral monodeiodination of levothyroxine (T4) at the 5 position (inner ring) also results in the formation of reverse liothyronine (T3), which is calorigenically inactive.

Liothyronine (T3) levels are low in the fetus and newborn, in old age, in chronic caloric deprivation, hepatic cirrhosis, renal failure, surgical stress, and chronic illnesses representing what has been called the “T3 thyronine syndrome.”

Pharmacokinetics

Animal studies have shown that levothyroxine (T4) is only partially absorbed from the gastrointestinal tract. The degree of absorption is dependent on the vehicle used for its administration and by the character of the intestinal contents, the intestinal flora, including plasma protein, and soluble dietary factors, all of which bind thyroid and thereby make it unavailable for diffusion. Only 41 percent is absorbed when given in a gelatin capsule as opposed to a 74 percent absorption when given with an albumin carrier.

Depending on other factors, absorption has varied from 48 to 79 percent of the administered dose. Fasting increases absorption. Malabsorption syndromes, as well as dietary factors, (children's soybean formula, concomitant use of anionic exchange resins such as cholestyramine) cause excessive fecal loss. Liothyronine (T3) is almost totally absorbed, 95 percent in 4 hours. The hormones contained in the natural preparations are absorbed in a manner similar to the synthetic hormones.

More than 99 percent of circulating hormones are bound to serum proteins, including thyroid-binding globulin (TBg), thyroid-binding prealbumin (TBPA), and albumin (TBa), whose capacities and affinities vary for the hormones. The higher affinity of levothyroxine (T4) for both TBg and TBPA as compared to liothyronine (T3) partially explains the higher serum levels and longer half-life of the former hormone. Both protein-bound hormones exist in reverse equilibrium with minute amounts of free hormone, the latter accounting for the metabolic activity.

Deiodination of levothyroxine (T4) occurs at a number of sites, including liver, kidney, and other tissues. The conjugated hormone, in the form of glucuronide or sulfate, is found in the bile and gut where it may complete an enterohepatic circulation. Eighty-five percent of levothyroxine (T4) metabolized daily is deiodinated.

Adverse reactions other than those indicative of hyperthyroidism because of therapeutic overdosage, either initially or during the maintenance period, are rare (See .

Patients on thyroid hormone preparations and parents of children on thyroid therapy should be informed that:

1. Replacement therapy is to be taken essentially for life, with the exception of cases of transient hypothyroidism, usually associated with thyroiditis, and in those patients receiving a therapeutic trial of the drug.
2. They should immediately report, during the course of therapy, any signs or symptoms of thyroid hormone toxicity, e.g., chest pain, increased pulse rate, palpitations, excessive sweating, heat intolerance, nervousness, or any other unusual event.
3. In case of concomitant diabetes mellitus, the daily dosage of antidiabetic medication may need readjustment as thyroid hormone replacement is achieved. If thyroid medication is stopped, a downward readjustment of the dosage of insulin or oral hypoglycemic agent may be necessary to avoid hypoglycemia. At all times, close monitoring of urinary glucose levels is mandatory in such patients.
4. In case of concomitant oral anticoagulant therapy, the prothrombin time should be measured frequently to determine if the dosage of oral anticoagulants is to be readjusted.
5. Partial loss of hair may be experienced by children in the first few months of thyroid therapy, but this is usually a transient phenomenon and later recovery is usually the rule.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

If you also take cholestyramine (Prevalite, Questran) or colestipol (Colestid), avoid taking these medications within 4 hours before or after you take desiccated thyroid.

Avoid taking an antacid within 4 hours before or after you take desiccated thyroid. Some antacids can make it harder for your body to absorb desiccated thyroid.

Your pharmacist can provide more information about desiccated thyroid.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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• Hypothyroidism