Source:http://www4.wiwiss.fu-berlin.de/dailymed/resource/drugs/1250
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Cytomel (Tablet)
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The dosage of thyroid hormones is determined by the indication
and must in every case be individualized according to patient response and
laboratory findings. Cytomel (liothyronine sodium)
Tablets are intended for oral administration; once-a-day dosage is recommended.
Although liothyronine sodium has a rapid cutoff, its metabolic effects persist
for a few days following discontinuance.<br/>Mild Hypothyroidism: Recommended starting dosage is 25 mcg daily. Daily dosage
then may be increased by up to 25 mcg every 1 or 2 weeks. Usual maintenance
dose is 25 to75 mcg daily. The rapid onset and dissipation
of action of liothyronine sodium (T), as compared with levothyroxine
sodium (T), has led some clinicians to prefer its use in patients
who might be more susceptible to the untoward effects of thyroid medication.
However, the wide swings in serum Tlevels that follow its administration
and the possibility of more pronounced cardiovascular side effects tend to
counterbalance the stated advantages. Cytomel (liothyronine
sodium) Tablets may be used in preference to levothyroxine (T)
during radioisotope scanning procedures, since induction of hypothyroidism
in those cases is more abrupt and can be of shorter duration. It may also
be preferred when impairment of peripheral conversion of Tto
Tis suspected.<br/>Myxedema: Recommended starting dosage is 5 mcg daily. This may be increased
by 5 to 10 mcg daily every 1 or 2 weeks. When 25 mcg daily is reached, dosage
may be increased by 5 to 25 mcg every 1 or 2 weeks until a satisfactory therapeutic
response is attained. Usual maintenance dose is 50 to 100 mcg daily.<br/>Myxedema Coma: Myxedema coma is usually precipitated in the hypothyroid
patient of long standing by intercurrent illness or drugs such as sedatives
and anesthetics and should be considered a medical emergency. An
intravenous preparation of liothyronine sodium is marketed by Jones Pharma
Incorporated, under the trade name Triostat for use in myxedema
coma/precoma.<br/>Congenital Hypothyroidism: Recommended starting dosage is 5 mcg daily, with a 5 mcg
increment every 3 to 4 days until the desired response is achieved. Infants
a few months old may require only 20 mcg daily for maintenance. At 1 year,
50 mcg daily may be required. Above 3 years, full adult dosage may be necessary
.<br/>Simple (non-toxic) Goiter: Recommended starting dosage is 5 mcg daily. This dosage may
be increased by 5 to 10 mcg daily every 1 or 2 weeks. When 25 mcg daily is
reached, dosage may be increased every week or two by 12.5 or 25 mcg. Usual
maintenance dosage is 75 mcg daily. In
the elderly or in pediatric patients, therapy should be started
with 5 mcg daily and increased only by 5 mcg increments at the recommended
intervals. When switching
a patient to Cytomel (liothyronine sodium) Tablets from thyroid,
L-thyroxine or thyroglobulin, discontinue the other medication, initiate Cytomel
at a low dosage, and increase gradually according to the patient's response.
When selecting a starting dosage, bear in mind that this drug has a rapid
onset of action, and that residual effects of the other thyroid preparation
may persist for the first several weeks of therapy.<br/>Thyroid Supression Therapy: Administration of thyroid hormone in doses higher than those
produced physiologically by the gland results in suppression of the production
of endogenous hormone. This is the basis for the thyroid suppression test
and is used as an aid in the diagnosis of patients with signs of mild hyperthyroidism
in whom baseline laboratory tests appear normal or to demonstrate thyroid
gland autonomy in patients with Graves' ophthalmopathy.I
uptake is determined before and after the administration of the exogenous
hormone. A 50% or greater suppression of uptake indicates a normal thyroid-pituitary
axis and thus rules out thyroid gland autonomy. Cytomel
(liothyronine sodium) Tablets are given in doses of 75 to 100 mcg/day for
7 days, and radioactive iodine uptake is determined before and after administration
of the hormone. If thyroid function is under normal control, the radioiodine
uptake will drop significantly after treatment. Cytomel (liothyronine sodium)
Tablets should be administered cautiously to patients in whom there is a strong
suspicion of thyroid gland autonomy, in view of the fact that the exogenous
hormone effects will be additive to the endogenous source.
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| dailymed-instance:descripti... |
Thyroid hormone drugs are natural or synthetic preparations
containing tetraiodothyronine (T, levothyroxine) sodium or triiodothyronine
(T, liothyronine) sodium or both. Tand Tare
produced in the human thyroid gland by the iodination and coupling of the
amino acid tyrosine. Tcontains four iodine atoms and is formed
by the coupling of two molecules of diiodotyrosine (DIT). Tcontains
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. Iodinecontent is only an indirect indicator
of true hormonal biologic activity. Cytomel (liothyronine
sodium) Tablets contain liothyronine (L-triiodothyronine or LT),
a synthetic form of a natural thyroid hormone, and is available as the sodium
salt. The structural and empirical formulas and molecular
weight of liothyronine sodium are given below. Liothyronine
Sodium L-Tyrosine, O-(4-hydroxy-3-iodophenyl)-3,5-diiodo-, monosodium salt Twenty-five
mcg of liothyronine is equivalent to approximately 1 grain 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 KPI and 115;
25 mcg scored and debossed KPI and 116; 50 mcg scored and debossed KPI and
117. Inactive ingredients consist of calcium sulfate, gelatin, starch, stearic
acid, sucrose and talc.
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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 inthe body and are of particular importance in the
development of the central nervous system.<br/>Pharmacokinetics: Since liothyronine sodium (T) is not firmly bound
to serum protein, it is readily available to body tissues. The onset of activity
of liothyronine sodium is rapid, occurring within a few hours. Maximum pharmacologic
response occurs within 2 or 3 days, providing early clinical response. The
biological half-life is about 2-1/2 days. Tis
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. Liothyronine sodium has a rapid cutoff of
activity which permits quick dosage adjustment and facilitates control of
the effects of overdosage, should they occur. The higher
affinity of levothyroxine (T) for both thyroid-binding globulin
and thyroid-binding prealbumin as compared to triiodothyronine (T)
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.
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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.
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Cytomel (liothyronine sodium) Tablets: 5 mcg in bottles
of 100; 25 mcg in bottles of 100; and 50 mcg in bottles of 100. 5
mcg 100's: NDC 60793-115-01 25 mcg 100's:
NDC 60793-116-01 50 mcg 100's: NDC 60793-117-01 Store
between 15��and 30��C (59��and 86��F). Prescribing
Information as of March 2004. Manufactured by: King
Pharmaceuticals, Inc., Bristol, TN 37620
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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.
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General: Thyroid hormone therapy in patients with concomitant diabetes
mellitus or insipidus or adrenal cortical insufficiency aggravates the intensity
of their symptoms. Appropriate adjustments of the various therapeutic measures
directed at these concomitant endocrine diseases are required. The
therapy of myxedema coma requires simultaneous administration of glucocorticoids. Hypothyroidism
decreases and hyperthyroidism increases the sensitivity to oral anticoagulants.
Prothrombin time should be closely monitored in thyroid-treated patients on
oral anticoagulants and dosage of the latter agents adjusted on the basis
of frequent prothrombin time determinations. In infants, excessive doses of
thyroid hormone preparations may produce craniosynostosis.<br/>Information for Patients: Patients on thyroid hormone preparations and parents of
pediatric patients on thyroid therapy should be informed that:<br/>Laboratory Tests: Treatment of patients with thyroid hormones requires the
periodic assessment of thyroid status by means of appropriate laboratory tests
besides the full clinical evaluation. The TSH suppression test can be used
to test the effectiveness of any thyroid preparation, bearing in mind the
relative insensitivity of the infant pituitary to the negative feedback effect
of thyroid hormones. Serum Tlevels can be used to test the effectiveness
of all thyroid medications except products containing liothyronine sodium.
When the total serum Tis low but TSH is normal, a test specific
to assess unbound (free) Tlevels is warranted. Specific measurements
of Tand Tby competitive protein binding or radioimmunoassay
are not influenced by blood levels of organic or inorganic iodine and have
essentially replaced older tests of thyroid hormone measurements, i.e., PBI,
BEI and Tby column.<br/>Drug Interactions:<br/>Oral Anticoagulants: Thyroid hormones appear to increase catabolism of vitamin
K-dependent clotting factors. If oral anticoagulants are also being given,
compensatory increases in clotting factor synthesis are impaired. Patients
stabilized on oral anticoagulants who are found to require thyroid replacement
therapy should be watched very closely when thyroid is started. Ifa patient
is truly hypothyroid, it is likely that a reduction in anticoagulant dosage
will be required. No special precautions appear to be necessary when oral
anticoagulant therapy is begun in a patient already stabilized on maintenance
thyroid replacement therapy.<br/>Insulin or Oral Hypoglycemics: Initiating thyroid replacement therapy may cause increases
in insulin or oral hypoglycemic requirements. The effects seen are poorly
understood and depend upon a variety of factors such as dose and type of thyroid
preparations and endocrine status of the patient. Patients receiving insulin
or oral hypoglycemics should be closely watched during initiation of thyroid
replacement therapy.<br/>Cholestyramine: Cholestyramine binds both Tand Tin
the intestine, thus impairing absorption of these thyroid hormones. In vitro studies indicate that the binding is
not easily removed. Therefore, 4 to 5 hours should elapse between administration
of cholestyramine and thyroid hormones.<br/>Estrogen, Oral Contraceptives: Estrogens tend to increase serum thyroxine-binding globulin
(TBg). In a patient with a nonfunctioning thyroid gland who is receiving thyroid
replacement therapy, free levothyroxine may be decreased when estrogens are
started thus increasing thyroid requirements. However, if the patient's
thyroid gland has sufficient function, the decreased free thyroxine will result
ina compensatory increase in thyroxine output by the thyroid. Therefore,
patients without a functioning thyroid gland who are on thyroid replacement
therapy may need to increase their thyroid dose if estrogens or estrogen-containing
oral contraceptives are given.<br/>Tricyclic Antidepressants: Use of thyroid products with imipramine and other tricyclic
antidepressants may increase receptor sensitivity and enhance antidepressant
activity; transient cardiac arrhythmias have been observed. Thyroid hormone
activity may also be enhanced.<br/>Digitalis: Thyroid preparations may potentiate the toxic effects of
digitalis. Thyroid hormonal replacement increases metabolic rate, which requires
an increase in digitalis dosage.<br/>Ketamine: When administered to patients on a thyroid preparation, this
parenteral anesthetic may cause hypertension and tachycardia. Use with caution
and be prepared to treat hypertension, if necessary.<br/>Vasopressors: Thyroxine increases the adrenergic effect of catecholamines
such as epinephrine and norepinephrine. Therefore, injection of these agents
into patients receiving thyroid preparations increases the risk of precipitating
coronary insufficiency, especially in patients with coronary artery disease.
Careful observation is required.<br/>Drug and Laboratory Test Interactions: The following drugs or moieties are known to interfere with
laboratory tests performed in patients on thyroid hormone therapy: androgens,
corticosteroids, estrogens, oral contraceptives containing estrogens, iodine-containing
preparations and the numerous preparations containing salicylates.<br/>Carcinogenesis, Mutagenesis, Impairment of Fertility: A reportedly apparent association between prolonged thyroid
therapy and breast cancer has not been confirmed and patients on thyroid for
established indications should not discontinue therapy. No confirmatory long-term
studies in animals have been performed to evaluate carcinogenic potential,
mutagenicity, or impairment of fertility in either males or females.<br/>Pregnancy:<br/>Category A: Thyroid hormones do not readily cross the placental barrier.
The clinical experience to date does not indicate any adverse effect on fetuses
when thyroid hormones are administered to pregnant women. On the basis of
current knowledge, thyroid replacement therapy to hypothyroid women should
not be discontinued during pregnancy.<br/>Nursing Mothers: Minimal amounts of thyroid hormones are excreted in human
milk. Thyroid is not associated with serious adverse reactions and does not
have a known tumorigenic potential. However, caution should be exercised when
thyroid is administered to a nursing woman.<br/>Geriatric Use: Clinical studies of liothyronine sodium did not include sufficient
numbers of subjects aged 65 and over to determine whether they respond differently
from younger subjects. Other reported clinical experience has not identified
differences in responses between the elderly and younger patients. In general,
dose selection for an elderly patient should be cautious, usually starting
at the low end of the dosing range, reflecting the greater frequency of decreased
hepatic, renal, or cardiac function, and of concomitant disease or other drug
therapy. This drug is known to be substantially excreted by the kidney, and
the risk of toxic reactions to this drug may be greater in patients with impaired
renal function. Because elderly patients are more likely to have decreased
renal function, care should be taken in dose selection, and it may be useful
to monitor renal function.<br/>Pediatric Use: Pregnant mothers provide little or no thyroid hormone to
the fetus. The incidence of congenital hypothyroidism is relatively high (1:4000)
and the hypothyroid fetus would not derive any benefit from the small amounts
of hormone crossing the placental barrier. Routine determinations of serum
Tand/or TSH is strongly advised in neonates in view of the deleterious
effects of thyroid deficiency on growth and development. Treatment
should be initiated immediately upon diagnosis and maintained for life, unless
transient hypothyroidism is suspected, in which case, therapy may be interrupted
for 2 to 8 weeks after the age of 3 years to reassess the condition. Cessation
of therapy is justified in patients who have maintained a normal TSH during
those 2 to 8 weeks.
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liothyronine sodium
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Cytomel (Tablet)
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Adverse reactions, other than those indicative of hyperthyroidism
because of therapeutic overdosage, either initially or during the maintenance
period are rare . In
rare instances, allergic skin reactions have been reported with Cytomel (liothyronine
sodium) Tablets.
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| dailymed-instance:warning |
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. 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 occult cardiac disease. In these patients, liothyronine
sodium therapy should be initiated with low doses, with due consideration
for its relatively rapid onset of action. Starting dosage of Cytomel (liothyronine
sodium) Tablets is 5 mcg daily, and should be increased by no more than 5
mcg increments at 2-week intervals.When, in such patients, a euthyroid state
can only be reached at the expense of an aggravation of the cardiovascular
disease, thyroid hormone dosage should be reduced. Morphologic
hypogonadism and nephrosis should be ruled out before the drug is administered.
If hypopituitarism is present, the adrenal deficiency must be corrected prior
to starting the drug. Myxedematous patients are very sensitive to thyroid;
dosage should be started at a very low level and increased gradually. Severe
and prolonged hypothyroidism can lead to a decreased level of adrenocortical
activity commensurate with the lowered metabolic state. When thyroid-replacement
therapy is administered, the metabolism increases at a greater rate than adrenocortical
activity. This can precipitate adrenocortical insufficiency. Therefore, in
severe and prolonged hypothyroidism, supplemental adrenocortical steroids
may be necessary. In rare instances the administration of thyroid hormone
may precipitate ahyperthyroid state or may aggravate existing hyperthyroidism.
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Thyroid hormone drugs are indicated: Cytomel (liothyronine sodium) Tablets can be used in patients
allergic to desiccated thyroid or thyroid extract derived from pork or beef.
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Cytomel
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