DESCRIPTION
Thyroid hormone drugs are natural or synthetic preparations
containing tetraiodothyronine (T4, levothyroxine) sodium
or triiodothyronine (T3, liothyronine) sodium or both.
T4 and T3 are produced in the human thyroid gland by the
iodination and coupling of the amino acid tyrosine T4
contains four iodine atoms and is formed by the coupling
of two molecules of diiodotyrosine (DIT). T3 contains
three atoms of iodine and is formed by the coupling of
one molecule of DIT with one molecule of monoiodotyrosine
(MIT). Both hormones are stored in the thyroid colloid
as thyroglobulin.
Thyroid hormone preparations belong to two categories
(1) natural hormonal preparations derived from animal
thyroid, and (2) synthetic preparations. Natural preparations
include desiccated thyroid and thyroglobulin. Desiccated
thyroid is derived from domesticated animals that are
used for food by man (either beef or hog thyroid) and
thyroglobulin is derived from thyroid glands of the hog.
The United States Pharmacopeia (USP) has standardized
the total iodine content of natural preparations. Thyroid
USP contains not less than (NLT) 0.17 percent and not
more than (NMT) 0.23 percent iodine, and thyroglobulin
contains not less than (NLT) 0.7 percent of organically
bound iodine. Iodine content is only an indirect indicator
of true hormonal biologic activity.
Cytomel (liothyronine sodium) Tablets contain liothyronine
(L-triiodothryonine or LT3), a synthetic form of a natural
thyroid hormone, and is available as the sodium salt.
The empirical formula and molecular weight of liothyronine
sodium are given below.
| C15H11I3NNaO4 |
|
M.W. 672.96 |
L-Tyrosine, O-(4-hydroxy-3-iodophenyl)-3,5-diiodo monosodium
salt
Twenty-five mcg of liothyronine is equivalent to approximately
1 gram of desiccated thyroid or thyroglobulin and 0.1
mg of L-thyroxine.
Each round, white to off-white Cytomel (liothyronine
sodium) tablet contains liothyronine sodium equivalent
to liothyronine as follows:
5 mcg debossed SKF and D14; 25 mcg scored and debossed
SKF and D16; 50 mcg scored and debossed SKF and D17. Inactive
ingredients consist of calcium sulfate, gelatin, starch,
stearic acid, sucrose and talc.
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