TF.G4.2.28.14
30
BIO-THROID
NP THYROID (THYROID TABLETS, USP) Bio-throid
RX ONLY
NP Thyroid (thyroid tablets, USP) for oral use is a natural preparation derived from porcine thyroid glands. They contain both tetraiodothyronine
sodium (T4 levothyroxine) and triiodothyronine sodium (T3 liothyronine) providing 38 mcg levothyroxine (T4) and 9 mcg liothyronine (T3)
per grain of thyroid (or per 65 mg of the labeled amount of thyroid). The inactive ingredients are calcium stearate, dextrose monohydrate,
maltodextrin and mineral oil.
CLINICAL PHARMACOLOGY
: 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 affected 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 liodothyronine (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
triiodothyronine comes from monodeiodination of levothyroxine. Peripheral monodeiodination of levothyroxine at the 5 position (inner ring) also
results in the formation of reverse triiodothyronine (T3), which is calorigenically inactive. Triiodothyronine (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 T4 is only partially absorbed from the gastro- intestinal 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 lbumin 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. 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 triiodothyronine (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.
INDICATIONS AND USAGE:
NP Thyroid tablets (thyroid tablets, USP) are indicated: 1. As replacement or supplemental therapy in patients
with hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis. This category includes
cretinism, myxedema, and ordinary hypothyroidism in patients of any age (children, adults, the elderly), or state (including pregnancy); primary
hypothyroidism resulting from functional deficiency, primary atrophy, partial or total absence of thyroid gland, or the effects of surgery, radiation,
or drugs, with or without the presence of goiter; and secondary (pituitary), or tertiary (hypothalamic) hypothyroidism (See WARNINGS). 2. As
pituitary TSH suppressants, in the treatment or prevention of various types of euthyroid goiters, including thyroid nodules, subacute or chronic
Iymphocytic thyroiditis (Hashimoto’s), multinodular goiter, and in the management of thyroid cancer. 3. As diagnostic agents in suppression tests
to differentiate suspected mild hyperthyroidism or thyroid gland autonomy.
CONTRAINDICATIONS
: Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal
cortical insufficiency, untreated thyrotoxicosis, and apparent hypersensitivity to any of their active or extraneous constituents. There is no well
documented evidence from the literature, however, of true allergic or idiosyncratic reactions to thyroid hormone.
WARNINGS
Drugs with thyroid hormone activity, alone or together with other
therapeutic agents, have been used for the treatment of obesity. In
euthyroid patients, doses within the range of daily hormonal
requirements are ineffective for weight reduction. Larger doses may
produce
serious or even life-threatening manifestations of toxicity, particularly
when given in association with sympathomimetic amines such as
those used for their anorectic effects.
The use of thyroid hormones in the therapy of obesity, alone or
combined with other drugs, is unjustified and has been shown to be
ineffective. Neither is their use justified for the treatment of male or
female infertility unless this condition is accompanied by
hypothyroidism
PRECAUTIONS: General
— Thyroid hormones should be used with great caution in a number of circumstances where the integrity of the
cardiovascular system, particularly the coronary arteries, is suspected. These include patients with angina pectoris or the elderly, in whom
there is a greater likelihood of acute cardiac disease. In these patients therapy should be initiated with low doses, i.e., 15-30 mg NP Thyroid.
When, in such patients, a euthyroid state can only be reached at the expense of an aggravation of the cardiovascular disease, thyroid hormone
