Source:http://www4.wiwiss.fu-berlin.de/dailymed/resource/drugs/464
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SYNTHROID (Tablet)
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General Principles: The goal of replacement
therapy is to achieve and maintain a clinical and biochemical euthyroid
state. The goal of suppressive therapy is to inhibit growth and/or
function of abnormal thyroid tissue. The dose of SYNTHROID that is
adequate to achieve these goals depends on a variety of factors including
the patient's age, body weight, cardiovascular status, concomitant
medical conditions, including pregnancy, concomitant medications,
and the specific nature of the condition being treated (see WARNINGS and PRECAUTIONS). Hence, the following recommendations serve
only as dosing guidelines. Dosing must be individualized and adjustments
made based on periodic assessment of the patient's clinical response
and laboratory parameters (see PRECAUTIONS
- Laboratory Tests). SYNTHROID is administered as a single daily dose, preferably one-half
to one-hour before breakfast. SYNTHROID should be taken at least
4 hours apart from drugs that are known to interfere with its absorption
(see PRECAUTIONS - Drug Interactions). Due to
the long half-life of levothyroxine, the peak therapeutic effect at
a given dose of levothyroxine sodium may not be attained for 4-6 weeks. Caution should be exercised
when administering SYNTHROID to patients with underlying cardiovascular
disease, to the elderly, and to those with concomitant adrenal insufficiency
(see PRECAUTIONS ).<br/>Specific Patient Populations:<br/>Hypothyroidism in Adults and in Children in Whom Growth and
Puberty are Complete: (see WARNINGS and PRECAUTIONS - Laboratory Tests) Therapy
may begin at full replacement doses in otherwise healthy individuals
less than 50 years old and in those older than 50 years who have been
recently treated for hyperthyroidism or who have been hypothyroid
for only a short time (such as a few months). The average full replacement
dose of levothyroxine sodium is approximately 1.7 mcg/kg/day (e.g., 100-125 mcg/day for a 70 kg adult). Older
patients may require less than 1 mcg/kg/day. Levothyroxine sodium
doses greater than 200 mcg/day are seldom required. An inadequate
response to daily doses���300 mcg/day is rare and may indicate
poor compliance, malabsorption, and/or drug interactions. For most patients
older than 50 years or for patients under 50 years of age with underlying
cardiac disease, an initial starting dose of 25-50 mcg/day of levothyroxine sodium is recommended,
with gradual increments in dose at 6-8 week intervals, as needed.
The recommended starting dose of levothyroxine sodium in elderly
patients with cardiac disease is 12.5-25
mcg/day , with gradual dose increments at 4-6 week intervals.
The levothyroxine sodium dose is generally adjusted in 12.5-25 mcg
increments until the patient with primary hypothyroidism is clinically
euthyroid and the serum TSH has normalized. In patients with severe hypothyroidism, the recommended initial levothyroxine
sodium dose is 12.5-25 mcg/day with increases of 25 mcg/day every 2-4 weeks, accompanied by clinical
and laboratory assessment, until the TSH level is normalized. In patients with
secondary (pituitary) or tertiary (hypothalamic) hypothyroidism, the
levothyroxine sodium dose should be titrated until the patient is
clinically euthyroid and the serum free- Tlevel is restored
to the upper half of the normal range.<br/>Pediatric Dosage - Congenital or Acquired Hypothyroidism: (see PRECAUTIONS - Laboratory Tests)<br/>Pregnancy: Pregnancy may increase levothyroxine requirements (see PREGNANCY).<br/>Subclinical Hypothyroidism: If this condition is treated, a lower levothyroxine sodium dose (e.g., 1 mcg/kg/day) than that used for full replacement
may be adequate to normalize the serum TSH level. Patients who are
not treated should be monitored yearly for changes in clinical status
and thyroid laboratory parameters.<br/>TSH Suppression in Well-differentiated Thyroid Cancer and Thyroid
Nodules: The target level for TSH suppression in these conditions has not
been established with controlled studies. In addition, the efficacy
of TSH suppression for benign nodular disease is controversial. Therefore,
the dose of SYNTHROID used for TSH suppression should be individualized
based on the specific disease and the patient being treated. In the treatment
of well-differentiated (papillary and follicular) thyroid cancer,
levothyroxine is used as an adjunct to surgery and radioiodine therapy.
Generally, TSH is suppressed to<0.1 mU/L, and this usually
requires a levothyroxine sodium dose of greater than 2 mcg/kg/day. However, in patients with high-risk
tumors, the target level for TSH suppression may be<0.01
mU/L. In the treatment of benign nodules and nontoxic multinodular goiter,
TSH is generally suppressed to a higher target (e.g., 0.1 to either
0.5 or 1.0 mU/L) than that used for the treatment of thyroid cancer.
Levothyroxine sodium is contraindicated if the serum TSH is already
suppressed due to the risk of precipitating overt thyrotoxicosis (see CONTRAINDICATIONS - WARNINGS and PRECAUTIONS).<br/>Myxedema Coma: Myxedema coma is a life-threatening emergency characterized by poor
circulation and hypometabolism, and may result in unpredictable absorption
of levothyroxine sodium from the gastrointestinal tract. Therefore,
oral thyroid hormone drug products are not recommended to treat this
condition. Thyroid hormone products formulated for intravenous administration
should be administered.
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SYNTHROID (levothyroxine
sodium tablets, USP) contain synthetic crystalline L-3,3',5,5'-tetraiodothyronine
sodium salt [levothyroxine (T) sodium]. Synthetic Tis identical to that produced in the human thyroid gland.
Levothyroxine (T) sodium has an empirical formula of
CHIN NaO���HO, molecular weight
of 798.86 g/mol (anhydrous), and structural formula as shown:<br/>Inactive Ingredients: Acacia, confectioner's
sugar (contains corn starch), lactose monohydrate, magnesium stearate,
povidone, and talc. The following are the color additives by tablet
strength: Meets USP Dissolution Test 3
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Thyroid hormone synthesis
and secretion is regulated by the hypothalamic-pituitary-thyroid axis.
Thyrotropin-releasing hormone (TRH) released from the hypothalamus
stimulates secretion of thyrotropin-stimulating hormone, TSH, from
the anterior pituitary. TSH, in turn, is the physiologic stimulus
for the synthesis and secretion of thyroid hormones, L-thyroxine (T) and L-triiodothyronine (T), by the thyroid gland.
Circulating serum Tand Tlevels exert a
feedback effect on both TRH and TSH secretion. When serum Tand Tlevels increase, TRH and TSH secretion decrease.
When thyroid hormone levels decrease, TRH and TSH secretion increase. The mechanisms by which thyroid
hormones exert their physiologic actions are not completely understood,
but it is thought that their principal effects are exerted through
control of DNA transcription and protein synthesis. Tand Tdiffuse into the cell nucleus and bind to thyroid
receptor proteins attached to DNA. This hormone nuclear receptor
complex activates gene transcription and synthesis of messenger RNA
and cytoplasmic proteins. Thyroid hormones regulate multiple metabolic processes and play an
essential role in normal growth and development, and normal maturation
of the central nervous system and bone. The metabolic actions of
thyroid hormones include augmentation of cellular respiration and
thermogenesis, as well as metabolism of proteins, carbohydrates and
lipids. The protein anabolic effects of thyroid hormones are essential
to normal growth and development. The physiological actions of thyroid hormones are produced predominantly
by T, the majority of which (approximately 80%) is derived
from Tby deiodination in peripheral tissues. Levothyroxine, at doses individualized
according to patient response, is effective as replacement or supplemental
therapy in hypothyroidism of any etiology, except transient hypothyroidism
during the recovery phase of subacute thyroiditis. Levothyroxine is also effective in the suppression of pituitary TSH
secretion in the treatment or prevention of various types of euthyroid
goiters, including thyroid nodules, Hashimoto's thyroiditis,
multinodular goiter and, as adjunctive therapy in the management of
thyrotropin-dependent well-differentiated thyroid cancer (see INDICATIONS AND USAGE, PRECAUTIONS, and DOSAGE AND ADMINISTRATION).<br/>Pharmacokinetics:<br/>Absorption: Absorption
of orally administered Tfrom the gastrointestinal (GI)
tract ranges from 40% to 80%. The majority of the levothyroxine dose
is absorbed from the jejunum and upper ileum. The relative bioavailability
of SYNTHROID tablets, compared to an equal nominal dose of oral levothyroxine
sodium solution, is approximately 93%. Tabsorption is
increased by fasting, and decreased in malabsorption syndromes and
by certain foods such as soybean infant formula. Dietary fiber decreases
bioavailability of T. Absorption may also decrease with
age. In addition, many drugs and foods affect Tabsorption
(see PRECAUTIONS - Drug Interactions and Drug-Food Interactions ).<br/>Distribution: Circulating
thyroid hormones are greater than 99% bound to plasma proteins, including
thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA),
and albumin (TBA), whose capacities and affinities vary for each hormone.
The higher affinity of both TBG and TBPA for Tpartially
explains the higher serum levels, slower metabolic clearance, and
longer half-life of Tcompared to T. Protein-bound
thyroid hormones exist in reverse equilibrium with small amounts of
free hormone. Only unbound hormone is metabolically active. Many
drugs and physiologic conditions affect the binding of thyroid hormones
to serum proteins (see PRECAUTIONS - Drug
Interactions and Drug-Laboratory
Test Interactions). Thyroid hormones do not readily cross
the placental barrier (see PRECAUTIONS -
Pregnancy).<br/>Metabolism: Tis slowly eliminated (see Table 1). The major pathway of thyroid hormone metabolism is through sequential
deiodination. Approximately eighty-percent of circulating Tis derived from peripheral Tby monodeiodination. The
liver is the major site of degradation for both Tand
T, with Tdeiodination also occurring at a
number of additional sites, including the kidney and other tissues.
Approximately 80% of the daily dose of Tis deiodinated
to yield equal amounts of Tand reverse T(rT). Tand rTare further deiodinated
to diiodothyronine. Thyroid hormones are also metabolized via conjugation
with glucuronides and sulfates and excreted directly into the bile
and gut where they undergo enterohepatic recirculation.<br/>Elimination: Thyroid
hormones are primarily eliminated by the kidneys. A portion of the
conjugated hormone reaches the colon unchanged and is eliminated in
the feces. Approximately 20% of Tis eliminated in the
stool. Urinary excretion of Tdecreases with age.
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Levothyroxine is contraindicated
in patients with untreated subclinical (suppressed serum TSH level
with normal Tand Tlevels) or overt thyrotoxicosis
of any etiology and in patients with acute myocardial infarction.
Levothyroxine is contraindicated in patients with uncorrected adrenal
insufficiency since thyroid hormones may precipitate an acute adrenal
crisis by increasing the metabolic clearance of glucocorticoids (see PRECAUTIONS). SYNTHROID is contraindicated
in patients with hypersensitivity to any of the inactive ingredients
in SYNTHROID tablets (See DESCRIPTION -
Inactive Ingredients ).
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SYNTHROID (levothyroxine sodium
tablets, USP) are round, color coded, scored and debossed
with "SYNTHROID" on one side and potency on the other side. They
are supplied as follows:<br/>Storage Conditions: Store at 25��C
(77��F); excursions permitted to 15��-30��C (59��-86��F)
[see USP Controlled Room Temperature]. SYNTHROID tablets should be
protected from light and moisture.
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WARNING: Thyroid hormones, including SYNTHROID, either alone or with
other therapeutic agents, should not be used for the treatment of
obesity or for weight loss. 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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The signs and symptoms of
overdosage are those of hyperthyroidism (see PRECAUTIONS and ADVERSE REACTIONS). In addition, confusion and disorientation may occur. Cerebral
embolism, shock, coma, and death have been reported. Seizures have
occurred in a child ingesting 18 mg of levothyroxine. Symptoms may
not necessarily be evident or may not appear untilseveral days after
ingestion of levothyroxine sodium.<br/>Treatment of Overdosage: Levothyroxine sodium
should be reduced in dose or temporarily discontinued if signs or
symptoms of overdosage occur.<br/>Acute Massive Overdosage: This may
be a life-threatening emergency, therefore, symptomatic and supportive
therapy should be instituted immediately. If not contraindicated
(e.g., by seizures, coma, or loss of the gag reflex), the stomach
should be emptied by emesis or gastric lavage to decrease gastrointestinal
absorption. Activated charcoal or cholestyramine may also be used
to decrease absorption. Central and peripheral increased sympathetic
activity may be treated by administering��-receptor antagonists,
e.g., propranolol, provided there are no medical contraindications
to their use. Provide respiratory support as needed; control congestive
heart failure and arrhythmia; control fever, hypoglycemia, and fluid
loss as necessary. Large doses of antithyroid drugs (e.g., methimazole
or propylthiouracil) followed in one to two hours by large doses of
iodine may be given to inhibit synthesis and release of thyroid hormones.
Glucocorticoids may be given to inhibit the conversion of Tto T. Plasmapheresis, charcoal hemoperfusion and exchange
transfusion have been reserved for cases in which continued clinical
deterioration occurs despite conventional therapy. Because Tis highly protein bound, very little drug will be removed
by dialysis.
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levothyroxine sodium
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SYNTHROID (Tablet)
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Adverse reactions associated
with levothyroxine therapy are primarily those of hyperthyroidism
due to therapeutic overdosage (see PRECAUTIONS and OVERDOSAGE ). They include
the following:<br/>General: fatigue, increased
appetite, weight loss, heat intolerance, fever, excessive sweating;<br/>Central nervous system: headache, hyperactivity,
nervousness, anxiety, irritability, emotional lability, insomnia;<br/>Musculoskeletal: tremors, muscle
weakness;<br/>Cardiovascular: palpitations, tachycardia,
arrhythmias, increased pulse and blood pressure, heart failure, angina,
myocardial infarction, cardiac arrest;<br/>Respiratory: dyspnea;<br/>Gastrointestinal: diarrhea, vomiting,
abdominal cramps and elevations in liver function tests;<br/>Dermatologic: hair loss, flushing;<br/>Endocrine: decreased bone mineral
density;<br/>Reproductive: menstrual irregularities,
impaired fertility. Pseudotumor cerebri and slipped capital femoral epiphysis
have been reported in children receiving levothyroxine therapy. Overtreatment
may result in craniosynostosis in infants and premature closure of
the epiphyses in children with resultant compromised adult height. Seizures have been reported
rarely with the institution of levothyroxine therapy. Inadequate levothyroxine dosage
will produce or fail to ameliorate the signs and symptoms of hypothyroidism. Hypersensitivity reactions
to inactive ingredients have occurred in patients treated with thyroid
hormone products. These include urticaria, pruritus, skin rash, flushing,
angioedema, various GI symptoms (abdominal pain, nausea, vomiting
and diarrhea), fever, arthralgia, serum sickness and wheezing. Hypersensitivity
to levothyroxine itself is not known to occur.
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WARNING: Thyroid hormones, including SYNTHROID, either alone or with
other therapeutic agents, should not be used for the treatment of
obesity or for weight loss. 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. Levothyroxine sodium should not be used in the treatment
of male or female infertility unless this condition is associated
with hypothyroidism. In
patients with nontoxic diffuse goiter or nodular thyroid disease,
particularly the elderly or those with underlying cardiovascular disease,
levothyroxine sodium therapy is contraindicated if the serum TSH level
is already suppressed due to the risk of precipitating overt thyrotoxicosis
(see CONTRAINDICATIONS).If the
serum TSH level is not suppressed, SYNTHROID should be used with caution
in conjunction with careful monitoring of thyroid function for evidence
of hyperthyroidism and clinical monitoring for potential associated
adverse cardiovascular signs and symptoms of hyperthyroidism.
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Levothyroxine sodium is
used for the following indications:<br/>Hypothyroidism: As replacement or
supplemental therapy in congenital or acquired hypothyroidism of any
etiology, except transient hypothyroidism during the recovery phase
of subacute thyroiditis. Specific indications include: primary (thyroidal),
secondary (pituitary), and tertiary (hypothalamic) hypothyroidism
and subclinical hypothyroidism. Primary hypothyroidism may result
from functional deficiency, primary atrophy, partial or total congenital
absence of the thyroid gland, or from the effects of surgery, radiation,
or drugs, with or without the presence of goiter.<br/>Pituitary TSH Suppression: In the treatment
or prevention of various types of euthyroid goiters (see WARNINGS and PRECAUTIONS), including thyroid nodules (see WARNINGS and PRECAUTIONS ), subacute or chronic lymphocytic thyroiditis
(Hashimoto's thyroiditis), multinodular goiter (see WARNINGS and PRECAUTIONS) and, as an adjunct to surgery and radioiodine
therapy in the management of thyrotropin-dependent well-differentiated
thyroid cancer.
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SYNTHROID
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