Synthroid® (levothyroxine sodium tablets, usp)
Levothyroxine has a narrow therapeutic index. Regardless of the indication for use, careful dosage titration is necessary to avoid the
consequences of over- or under-treatment. These consequences include, among others, effects on growth and development, cardiovascularfunction, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid
(levothyroxine sodium tablets, USP)
metabolism. Many drugs interact with levothyroxine sodium necessitating adjustments in dosing to maintain therapeutic response
(see Drug Interactions
).Effects on bone mineral density-
In women, long-term levothyroxine sodium therapy has been associated with increased bone
resorption, thereby decreasing bone mineral density, especially in post-menopausal women on greater than replacement doses or in
SYNTHROID® (levothyroxine sodium tablets, USP) contain synthetic crystalline L-3,3’,5,5’-tetraiodothyronine sodium salt
women who are receiving suppressive doses of levothyroxine sodium. The increased bone resorption may be associated with
[levothyroxine (T4) sodium]. Synthetic T4 is identical to that produced in the human thyroid gland. Levothyroxine (T4) sodium has
increased serum levels and urinary excretion of calcium and phosphorous, elevations in bone alkaline phosphatase and suppressed
an empirical formula of C15H10I4N NaO4 • H2O, molecular weight of 798.86 g/mol (anhydrous), and structural formula as shown:
serum parathyroid hormone levels. Therefore, it is recommended that patients receiving levothyroxine sodium be given the minimumdose necessary to achieve the desired clinical and biochemical response.
Patients with underlying cardiovascular disease-
Exercise caution when administering levothyroxine to patients with cardiovascular
disorders and to the elderly in whom there is an increased risk of occult cardiac disease. In these patients, levothyroxine therapy
C COONa * xH
should be initiated at lower doses than those recommended in younger individuals or in patients without cardiac disease
, Geriatric Use
; and DOSAGE AND ADMINISTRATION
). If cardiac symptoms develop or
worsen, the levothyroxine dose should be reduced or withheld for one week and then cautiously restarted at a lower dose.
Overtreatment with levothyroxine sodium may have adverse cardiovascular effects such as an increase in heart rate, cardiac wall
acacia, confectioner’s sugar (contains corn starch), lactose monohydrate, magnesium stearate, povidone, and
thickness, and cardiac contractility and may precipitate angina or arrhythmias. Patients with coronary artery disease who are
talc. The following are the color additives by tablet strength:
receiving levothyroxine therapy should be monitored closely during surgical procedures, since the possibility of precipitating cardiac
arrhythmias may be greater in those treated with levothyroxine. Concomitant administration of levothyroxine and sympathomimeticagents to patients with coronary artery disease may precipitate coronary insufficiency.
Patients with nontoxic diffuse goiter or nodular thyroid disease-
Exercise caution when administering levothyroxine to patients with
nontoxic diffuse goiter or nodular thyroid disease in order to prevent precipitation of thyrotoxicosis (see WARNINGS
). If the serum
FD&C Red No. 40 Aluminum Lake, FD&C Blue No. 2 Aluminum Lake
TSH is already suppressed, levothyroxine sodium should not be administered (see CONTRAINDICATIONS
FD&C Blue No. 1 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake*, D&C Yellow No. 10 Aluminum Lake
Associated endocrine disorders
D&C Yellow No. 10 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake*
Hypothalamic/pituitary hormone deficiencies- In patients with secondary or tertiary hypothyroidism, additional
hypothalamic/pituitary hormone deficiencies should be considered, and, if diagnosed, treated (see PRECAUTIONS
D&C Red No. 27 & 30 Aluminum Lake
for adrenal insufficiency).
FD&C Yellow No. 6 Aluminum Lake*, FD&C Red No. 40 Aluminum Lake, FD&C Blue No. 1 Aluminum Lake
Autoimmune polyglandular syndrome- Occasionally, chronic autoimmune thyroiditis may occur in association with other
autoimmune disorders such as adrenal insufficiency, pernicious anemia, and insulin-dependent diabetes mellitus. Patients with
concomitant adrenal insufficiency should be treated with replacement glucocorticoids prior to initiation of treatment withlevothyroxine sodium. Failure to do so may precipitate an acute adrenal crisis when thyroid hormone therapy is initiated, due to
FD&C Blue No. 1 Aluminum Lake, D&C Red No. 27 & 30 Aluminum Lake
increased metabolic clearance of glucocorticoids by thyroid hormone. Patients with diabetes mellitus may require upward
adjustments of their antidiabetic therapeutic regimens when treated with levothyroxine (see PRECAUTIONS
, Drug Interactions
D&C Yellow No. 10 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake*, FD&C Blue No. 1 Aluminum Lake
Other associated medical conditions
Infants with congenital hypothyroidism appear to be at increased risk for other congenital anomalies, with cardiovascular anomalies
* Note - FD&C Yellow No. 6 is orange in color.
(pulmonary stenosis, atrial septal defect, and ventricular septal defect) being the most common association.
Information for Patients
Patients should be informed of the following information to aid in the safe and effective use of SYNTHROID:
Thyroid hormone synthesis and secretion is regulated by the hypothalamic-pituitary-thyroid axis. Thyrotropin-releasing hormone
1. Notify your physician if you are allergic to any foods or medicines, are pregnant or intend to become pregnant, are breast-feeding
(TRH) released from the hypothalamus stimulates secretion of thyrotropin-stimulating hormone, TSH, from the anterior pituitary.
or are taking any other medications, including prescription and over-the-counter preparations.
TSH, in turn, is the physiologic stimulus for the synthesis and secretion of thyroid hormones, L-thyroxine (T4) and L-triiodothyronine
2. Notify your physician of any other medical conditions you may have, particularly heart disease, diabetes, clotting disorders, and
(T3), by the thyroid gland. Circulating serum T3 and T4 levels exert a feedback effect on both TRH and TSH secretion. When serum T3
adrenal or pituitary gland problems. Your dose of medications used to control these other conditions may need to be adjusted
and T4 levels increase, TRH and TSH secretion decrease. When thyroid hormone levels decrease, TRH and TSH secretion increase.
while you are taking SYNTHROID. If you have diabetes, monitor your blood and/or urinary glucose levels as directed by your
The mechanisms by which thyroid hormones exert their physiologic actions are not completely understood, but it is thought that
physician and immediately report any changes to your physician. If you are taking anticoagulants (blood thinners), your clotting
their principal effects are exerted through control of DNA transcription and protein synthesis. T3 and T4 diffuse into the cell nucleus
status should be checked frequently.
and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and
3. Use SYNTHROID only as prescribed by your physician. Do not discontinue or change the amount you take or how often you take
synthesis of messenger RNA and cytoplasmic proteins.
it, unless directed to do so by your physician.
Thyroid hormones regulate multiple metabolic processes and play an essential role in normal growth and development, and normal
4. The levothyroxine in SYNTHROID is intended to replace a hormone that is normally produced by your thyroid gland. Generally,
maturation of the central nervous system and bone. The metabolic actions of thyroid hormones include augmentation of cellular
replacement therapy is to be taken for life, except in cases of transient hypothyroidism, which is usually associated with an
respiration and thermogenesis, as well as metabolism of proteins, carbohydrates and lipids. The protein anabolic effects of thyroid
inflammation of the thyroid gland (thyroiditis).
hormones are essential to normal growth and development.
5. Take SYNTHROID as a single dose, preferably on an empty stomach, one-half to one hour before breakfast. Levothyroxine
The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is
absorption is increased on an empty stomach.
derived from T4 by deiodination in peripheral tissues.
6. It may take several weeks before you notice an improvement in your symptoms.
Levothyroxine, at doses individualized according to patient response, is effective as replacement or supplemental therapy in
7. Notify your physician if you experience any of the following symptoms: rapid or irregular heartbeat, chest pain, shortness of
hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis.
breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting,
Levothyroxine is also effective in the suppression of pituitary TSH secretion in the treatment or prevention of various types of
diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives or skin rash, or any other unusual
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
8. Notify your physician if you become pregnant while taking SYNTHROID. It is likely that your dose of SYNTHROID will need to
and DOSAGE AND ADMINISTRATION
be increased while you are pregnant.
9. Notify your physician or dentist that you are taking SYNTHROID prior to any surgery.
– Absorption of orally administered T
10. Partial hair loss may occur rarely during the first few months of SYNTHROID therapy, but this is usually temporary.
4 from 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
11. SYNTHROID should not be used as a primary or adjunctive therapy in a weight control program.
equal nominal dose of oral levothyroxine sodium solution, is approximately 93%. T
12. Keep SYNTHROID out of the reach of children. Store SYNTHROID away from heat, moisture, and light.
4 absorption is increased by fasting, and decreased in
malabsorption syndromes and by certain foods such as soybean infant formula. Dietary fiber decreases bioavailability of T
13. Agents such as iron and calcium supplements and antacids can decrease the absorption of levothyroxine sodium tablets.
may also decrease with age. In addition, many drugs and foods affect T
Therefore, levothyroxine sodium tablets should not be administered within 4 hours of these agents.
4 absorption (see PRECAUTIONS
, Drug Interactions
– 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
The diagnosis of hypothyroidism is confirmed by measuring TSH levels using a sensitive assay (second generation assay sensitivity
≤ 0.1 mIU/L or third generation assay sensitivity ≤ 0.01 mIU/L) and measurement of free-T
4 partially explains the higher serum levels, slower metabolic clearance, and longer half-life of
T4 compared to T3. Protein-bound thyroid hormones exist in reverse equilibrium with small amounts of free hormone. Only unbound
The adequacy of therapy is determined by periodic assessment of appropriate laboratory tests and clinical evaluation. The choice
hormone is metabolically active. Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins
of laboratory tests depends on various factors including the etiology of the underlying thyroid disease, the presence of concomitant
, Drug Interactions
and Drug-Laboratory Test Interactions
). Thyroid hormones do not readily cross the
medical conditions, including pregnancy, and the use of concomitant medications (see PRECAUTIONS
, Drug Interactions and
placental barrier (see PRECAUTIONS
Drug-Laboratory Test Interactions
). Persistent clinical and laboratory evidence of hypothyroidism despite an apparent adequate
replacement dose of SYNTHROID may be evidence of inadequate absorption, poor compliance, drug interactions, or decreased T
4 is slowly eliminated (see Table 1
). The major pathway of thyroid hormone metabolism is through sequential
deiodination. Approximately eighty-percent of circulating T
3 is derived from peripheral T4 by monodeiodination. The liver is the
major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including the kidney
and other tissues. Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (rT3). T3 and
In adult patients with primary (thyroidal) hypothyroidism, serum TSH levels (using a sensitive assay) alone may be used to monitor
rT3 are further deiodinated to diiodothyronine. Thyroid hormones are also metabolized via conjugation with glucuronides and
therapy. The frequency of TSH monitoring during levothyroxine dose titration depends on the clinical situation but it is generally
sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation.
recommended at 6-8 week intervals until normalization. For patients who have recently initiated levothyroxine therapy and whose
– Thyroid hormones are primarily eliminated by the kidneys. A portion of the conjugated hormone reaches the colon
serum TSH has normalized or in patients who have had their dosage or brand of levothyroxine changed, the serum TSH concentration
unchanged and is eliminated in the feces. Approximately 20% of T
should be measured after 8-12 weeks. When the optimum replacement dose has been attained, clinical (physical examination) and
4 is eliminated in the stool. Urinary excretion of T4 decreases with age.
biochemical monitoring may be performed every 6-12 months, depending on the clinical situation, and whenever there is a change in
Table 1: Pharmacokinetic Parameters of
the patient’s status. It is recommended that a physical examination and a serum TSH measurement be performed at least annually in
Thyroid Hormones in Euthyroid Patients
patients receiving SYNTHROID (see WARNINGS
, and DOSAGE AND ADMINISTRATION
In patients with congenital hypothyroidism, the adequacy of replacement therapy should be assessed by measuring both serumTSH (using a sensitive assay) and total- or free- T
4. During the first three years of life, the serum total- or free- T4 should be
maintained at all times in the upper half of the normal range. While the aim of therapy is to also normalize the serum TSH level,
this is not always possible in a small percentage of patients, particularly in the first few months of therapy. TSH may not normalize
1 3 to 4 days in hyperthyroidism, 9 to 10 days in hypothyroidism
due to a resetting of the pituitary-thyroid feedback threshold as a result of in utero
hypothyroidism. Failure of the serum T4 to
increase into the upper half of the normal range within 2 weeks of initiation of SYNTHROID therapy and/or of the serum TSH todecrease below 20 mU/L within 4 weeks should alert the physician to the possibility that the child is not receiving adequate
INDICATIONS AND USAGE
therapy. Careful inquiry should then be made regarding compliance, dose of medication administered, and method of
Levothyroxine sodium is used for the following indications:
administration prior to raising the dose of SYNTHROID.
– As replacement or supplemental therapy in congenital or acquired hypothyroidism of any etiology, except transient
The recommended frequency of monitoring of TSH and total or free T4 in children is as follows: at 2 and 4 weeks after the initiation
hypothyroidism during the recovery phase of subacute thyroiditis. Specific indications include: primary (thyroidal), secondary
of treatment; every 1-2 months during the first year of life; every 2-3 months between 1 and 3 years of age; and every 3 to 12 months
(pituitary), and tertiary (hypothalamic) hypothyroidism and subclinical hypothyroidism. Primary hypothyroidism may result from
thereafter until growth is completed. More frequent intervals of monitoring may be necessary if poor compliance is suspected or
functional deficiency, primary atrophy, partial or total congenital absence of the thyroid gland, or from the effects of surgery, radiation,
abnormal values are obtained. It is recommended that TSH and T4 levels, and a physical examination, if indicated, be performed
or drugs, with or without the presence of goiter.
2 weeks after any change in SYNTHROID dosage. Routine clinical examination, including assessment of mental and physical growth
and development, and bone maturation, should be performed at regular intervals (see PRECAUTIONS
, Pediatric Use and DOSAGE
Pituitary TSH Suppression
– In the treatment or prevention of various types of euthyroid goiters (see WARNINGS
), including thyroid nodules (see WARNINGS
), subacute or chronic lymphocytic thyroiditis
(Hashimoto’s thyroiditis), multinodular goiter (see WARNINGS
) and, as an adjunct to surgery and radioiodine
Secondary (pituitary) and tertiary (hypothalamic) hypothyroidism
therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.
Adequacy of therapy should be assessed by measuring serum free-T4 levels, which should be maintained in the upper half of the
Levothyroxine is contraindicated in patients with untreated subclinical (suppressed serum TSH level with normal T
or overt thyrotoxicosis of any etiology and in patients with acute myocardial infarction. Levothyroxine is contraindicated in patients
Many drugs affect thyroid hormone pharmacokinetics and metabolism (e.g., absorption, synthesis, secretion, catabolism, protein
with uncorrected adrenal insufficiency since thyroid hormones may precipitate an acute adrenal crisis by increasing the metabolic
binding, and target tissue response) and may alter the therapeutic response to SYNTHROID. In addition, thyroid hormones and
clearance of glucocorticoids (see PRECAUTIONS
). SYNTHROID is contraindicated in patients with hypersensitivity to any of the
thyroid status have varied effects on the pharmacokinetics and actions of other drugs. A listing of drug-thyroidal axis interactions is
inactive ingredients in SYNTHROID tablets (See DESCRIPTION
, Inactive Ingredients
The list of drug-thyroidal axis interactions in Table 2 may not be comprehensive due to the introduction of new drugs that interact
with the thyroidal axis or the discovery of previously unknown interactions. The prescriber should be aware of this fact and shouldconsult appropriate reference sources (e.g., package inserts of newly approved drugs, medical literature) for additional information if
a drug-drug interaction with levothyroxine is suspected.
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 withhypothyroidism.
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.
Table 2: Drug-Thyroidal Axis Interactions
Table 2: continued
Drug or Drug Class
Drug or Drug Class
Drugs that may reduce TSH secretion –the reduction is not sustained; therefore, hypothyroidism does not occur
Use of these agents may result in a transient reduction in TSH secretion when
Thyroid hormones may reduce the uptake of 123I, 131I, and 99mTc.
administered at the following doses: Dopamine (≥ 1 mcg/kg/min); Glucocorticoids
(hydrocortisone ≥ 100 mg/day or equivalent); Octreotide (> 100 mcg/day).
Concurrent use may increase the effects of sympathomimetics or thyroid hormone. Thyroidhormones may increase the risk of coronary insuf ficiency when sympathomimetic agents are
Drugs that alter thyroid hormone secretion
administered to patients with coronary artery disease.
Drugs that may decrease thyroid hormone secretion, which may result in hypothyroidism
These agents have been associated with thyroid hormone and/or TSH level alterations by
Long-term lithium therapy can result in goiter in up to 50% of patients, and either subclinical
or overt hypothyroidism, each in up to 20% of patients. The fetus, neonate, elderly and
euthyroid patients with underlying thyroid disease (e.g., Hashimoto’s thyroiditis or with
Grave’s disease previously treated with radioiodine or surgery) are among those individuals
who are particularly susceptible to iodine-induced hypo thyroidism. Oral cholecystographic
agents and amiodarone are slowly excreted, producing more prolonged hypothyroidism than
parenterally administered iodinated contrast agents. Long-term aminoglutethimide therapy
Sulfonamides may minimally decrease T4 and T3 levels and increase TSH, although all values remain
within normal limits in most patients.
Drugs that may increase thyroid hormone secretion, which may result in hyperthyroidism
Oral anticoagulants- Levothyroxine increases the response to oral anticoagulant therapy. Therefore, a decrease in the dose of anticoagulant
Iodide and drugs that contain pharmacologic amounts of iodide may cause hyperthyroidism
may be warranted with correction of the hypothyroid state or when the SYNTHROID dose is increased. Prothrombin time should be closely
in euthyroid patients with Grave’s disease previously treated with antithyroid drugs or in
monitored to permit appropriate and timely dosage adjustments (see Table 2
euthyroid patients with thyroid autonomy (e.g., multinodular goiter or hyper functioning
Digitalis glycosides- The therapeutic effects of digitalis glycosides may be reduced by levothyroxine. Serum digitalis glycoside levels
thyroid adenoma). Hyperthyroidism may develop over several weeks and may persist for
may be decreased when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides
several months after therapy discontinuation. Amiodarone may induce hyperthyroidism by
(see Table 2
– Consumption of certain foods may affect levothyroxine absorption thereby necessitating adjustments in dosing.
Drugs that may decrease T
4 absorption, which may result in hypothyroidism
Soybean flour (infant formula), cotton seed meal, walnuts, and dietary fiber may bind and decrease the absorption of levothyroxine sodiumfrom the GI tract.
Concurrent use may reduce the efficacy of levothyroxine by binding and delaying
or preventing absorption, potentially resulting in hypothyroidism. Calcium carbonate
Drug-Laboratory Test Interactions
– Changes in TBG concentration must be considered when interpreting T4 and T3 values, which
may form an insoluble chelate with levothyroxine, and ferrous sulfate likely forms a
necessitates measurement and evaluation of unbound (free) hormone and/or determination of the free T4 index (FT4I). Pregnancy,
ferric-thyroxine complex. Administer levothyroxine at least 4 hours apart from these
infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentrations.
agents. Patients treated concomitantly with orlistat and levothyroxine should be monitored
Decreases in TBG concentrations are observed in nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, and after
androgen or corticosteroid therapy (see also Table 2
). Familial hyper- or hypo-thyroxine binding globulinemias have been described,
with the incidence of TBG deficiency approximating 1 in 9000.
Carcinogenesis, Mutagenesis, and Impairment of Fertility
– Animal studies have not been performed to evaluate the carcinogenic
potential, mutagenic potential or effects on fertility of levothyroxine. The synthetic T4 in SYNTHROID is identical to that produced
naturally by the human thyroid gland. Although there has been a reported association between prolonged thyroid hormone therapy
and breast cancer, this has not been confirmed. Patients receiving SYNTHROID for appropriate clinical indications should be titrated
to the lowest effective replacement dose.
Pregnancy – Category A
– Studies in women taking levothyroxine sodium during pregnancy have not shown an increased risk of
Drugs that may alter T
congenital abnormalities. Therefore, the possibility of fetal harm appears remote. SYNTHROID should not be discontinued during
4 and T
3 serum transport - but FT
4 concentration remains normal; and therefore, the patient remains
pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated.
Hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion,
Drugs that may increase
Drugs that may decrease serum
pre-eclampsia, stillbirth and premature delivery. Maternal hypothyroidism may have an adverse effect on fetal and childhood growth
serum TBG concentration
and development. During pregnancy, serum T4 levels may decrease and serum TSH levels increase to values outside the normal
range. Since elevations in serum TSH may occur as early as 4 weeks gestation, pregnant women taking SYNTHROID should have
their TSH measured during each trimester. An elevated serum TSH level should be corrected by an increase in the dose of
SYNTHROID. Since postpartum TSH levels are similar to preconception values, the SYNTHROID dosage should return to the
pre-pregnancy dose immediately after delivery. A serum TSH level should be obtained 6-8 weeks postpartum.
Thyroid hormones cross the placental barrier to some extent as evidenced by levels in cord blood of athyreotic fetuses being
approximately one-third maternal levels. Transfer of thyroid hormone from the mother to the fetus, however, may not be adequate to
prevent in utero
– Although thyroid hormones are excreted only minimally in human milk, caution should be exercised when
SYNTHROID is administered to a nursing woman. However, adequate replacement doses of levothyroxine are generally needed to
Drugs that may cause protein-binding site displacement
Administration of these agents with levothyroxine results in an initial transient increase in
FT4. Continued administration results in a decrease in serum T4 and normal FT4 and TSH
concentrations and, therefore, patients are clinically euthyroid. Salicylates inhibit binding of
The goal of treatment in pediatric patients with hypothyroidism is to achieve and maintain normal intellectual and physical growth
T4 and T3 to TBG and transthyretin. An initial increase in serum FT4 is followed by return
of FT4 to normal levels with sustained therapeutic serum salicylate concentrations,
The initial dose of levothyroxine varies with age and body weight (see DOSAGE AND ADMINISTRATION, Table 3
although total-T4 levels may decrease by as much as 30%.
Dosing adjustments are based on an assessment of the individual patient’s clinical and laboratory parameters (see PRECAUTIONS,
In children in whom a diagnosis of permanent hypothyroidism has not been established, it is recommended that levothyroxine
administration be discontinued for a 30-day trial period, but only after the child is at least 3 years of age. Serum T
Drugs that may alter T
4 and T
should then be obtained. If the T4 is low and the TSH high, the diagnosis of permanent hypothyroidism is established,
Drugs that may increase hepatic metabolism, which may result in hypothyroidism
and levothyroxine therapy should be reinstituted. If the T4 and TSH levels are normal, euthyroidism may be assumed and, therefore,
the hypothyroidism can be considered to have been transient. In this instance, however, the physician should carefully monitor the
Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased
child and repeat the thyroid function tests if any signs or symptoms of hypothyroidism develop. In this setting, the clinician should
hepatic degradation of levothyroxine, resulting in increased levothyroxine requirements.
have a high index of suspicion of relapse. If the results of the levothyroxine withdrawal test are inconclusive, careful follow-up and
Phenytoin and carb amazepine reduce serum protein binding of levothyroxine, and total-
subsequent testing will be necessary.
and free- T4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels
Since some more severely affected children may become clinically hypothyroid when treatment is discontinued for 30 days,
an alternate approach is to reduce the replacement dose of levothyroxine by half during the 30-day trial period. If, after 30 days,
Drugs that may decrease T
the serum TSH is elevated above 20 mU/L, the diagnosis of permanent hypothyroidism is confirmed, and full replacement therapy
4 5’-deiodinase activity
should be resumed. However, if the serum TSH has not risen to greater than 20 mU/L, levothyroxine treatment should be
Administration of these enzyme inhibitors decreases the peripheral conversion of T4 to T3,
discontinued for another 30-day trial period followed by repeat serum T4 and TSH testing.
leading to decreased T3 levels. However, serum T4 levels are usually normal but may
The presence of concomitant medical conditions should be considered in certain clinical circumstances and, if present, appropriately
occasionally be slightly increased. In patients treated with large doses of propranolol
treated (see PRECAUTIONS
(> 160 mg/day), T3 and T4 levels change slightly, TSH levels remain normal, and patients are
Congenital Hypothyroidism (see PRECAUTIONS, Laboratory Tests and DOSAGE AND ADMINISTRATION
clinically euthyroid. It should be noted that actions of particular beta- adrenergic antagonists
may be impaired when the hypothyroid patient is converted to the euthyroid state.
4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on
intellectual development as well as on overall physical growth and maturation. Therefore, SYNTHROID therapy should be initiated
Short-term administration of large doses of glucocorticoids may decrease serum T3
immediately upon diagnosis and is generally continued for life.
concentrations by 30% with minimal change in serum T4 levels. However, long-term
During the first 2 weeks of SYNTHROID therapy, infants should be closely monitored for cardiac overload, arrhythmias, and
glucocorticoid therapy may result in slightly decreased T3 and T4 levels due to decreased
The patient should be monitored closely to avoid undertreatment or overtreatment. Undertreatment may have deleterious effects
on intellectual development and linear growth. Overtreatment has been associated with craniosynostosis in infants, and mayadversely affect the tempo of brain maturation and accelerate the bone age with resultant premature closure of the epiphyses and
Thyroid hormones appear to increase the catabolism of vitamin K-dependent clotting factors,
thereby increasing the anticoagulant activity of oral anticoagulants. Concomitant use of these
Acquired Hypothyroidism in Pediatric Patients
agents impairs the compensatory increases in clotting factor synthesis. Prothrombin time
The patient should be monitored closely to avoid undertreatment and overtreatment. Undertreatment may result in poor school
should be carefully monitored in patients taking levothyroxine and oral anticoagulants and
performance due to impaired concentration and slowed mentation and in reduced adult height. Overtreatment may accelerate the
the dose of anticoagulant therapy adjusted accordingly.
bone age and result in premature epiphyseal closure and compromised adult stature.
Concurrent use of tri/tetracyclic antidepressants and levothyroxine may increase the
Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height.
therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to
In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height.
catecholamines. Toxic effects may include increased risk of cardiac arrhythmias and CNS
stimulation; onset of action of tricyclics may be accelerated. Administration of sertra line in
Because of the increased prevalence of cardiovascular disease among the elderly, levothyroxine therapy should not be initiated at the
patients stabilized on levothyroxine may result in increased levothyroxine requirements.
full replacement dose (see WARNINGS, PRECAUTIONS,
and DOSAGE AND ADMINISTRATION
Addition of levothyroxine to antidiabetic or insulin therapy may result in increased
Adverse reactions associated with levothyroxine therapy are primarily those of hyperthyroidism due to therapeutic overdosage
antidiabetic agent or insulin requirements. Careful monitoring of diabetic control is
). They include the following:
recommended, especially when thyroid therapy is started, changed, or discon
fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating;
Central nervous system:
headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia;
tremors, muscle weakness;
palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial
infarction, cardiac arrest;
Serum digitalis glycoside levels may be reduced in hyperthyroidism or when the
hypothyroid patient is converted to the euthyroid state. Therapeutic effect of digitalis
diarrhea, vomiting, abdominal cramps and elevations in liver function tests;
hair loss, flushing;
Therapy with interferon-α has been associated with the development of antithyroid
decreased bone mineral density;
microsomal antibodies in 20% of patients and some have transient hypothyroidism,
menstrual irregularities, impaired fertility.
hyperthyroidism, or both. Patients who have antithyroid antibodies before treatment are at
Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children receiving levothyroxine therapy.
higher risk for thyroid dysfunction during treatment. Interleukin-2 has been associated with
Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in children with resultant
transient painless thyroiditis in 20% of patients. Inter feron-β and -γ have not been reported to
Seizures have been reported rarely with the institution of levothyroxine therapy.
Excessive use of thyroid hormones with growth hormones may accelerate epiphyseal closure.
Inadequate levothyroxine dosage will produce or fail to ameliorate the signs and symptoms of hypothyroidism.
However, untreated hypothyroidism may interfere with growth response to growth
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.
Concurrent use may produce marked hypertension and tachycardia; cautious administration
to patients receiving thyroid hormone therapy is recom mended.
The signs and symptoms of overdosage are those of hyperthyroidism (see PRECAUTIONS
and ADVERSE REACTIONS
Decreased theophylline clearance may occur in hypothyroid patients; clearance returns to
In addition, confusion and disorientation may occur. Cerebral embolism, shock, coma, and death have been reported. Seizures have
normal when the euthyroid state is achieved.
occurred in a child ingesting 18 mg of levothyroxine. Symptoms may not necessarily be evident or may not appear until several days
after ingestion of levothyroxine sodium.
Treatment of Overdosage
Levothyroxine sodium should be reduced in dose or temporarily discontinued if signs or symptoms of overdosage occur.
Acute Massive Overdosage
– This may be a life-threatening emergency, therefore, symptomatic and supportive therapy should be
TSH Suppression in Well-differentiated Thyroid Cancer and Thyroid Nodules
- The target level for TSH suppression in these conditions has
instituted immediately. If not contraindicated (e.g., by seizures, coma, or loss of the gag reflex), the stomach should be emptied by
not been established with controlled studies. In addition, the efficacy of TSH suppression for benign nodular disease is controversial.
emesis or gastric lavage to decrease gastrointestinal absorption. Activated charcoal or cholestyramine may also be used to decrease
Therefore, the dose of SYNTHROID used for TSH suppression should be individualized based on the specific disease and the patient
absorption. Central and peripheral increased sympathetic activity may be treated by administering β-receptor antagonists,
e.g., propranolol, provided there are no medical contraindications to their use. Provide respiratory support as needed; control
In the treatment of well-differentiated (papillary and follicular) thyroid cancer, levothyroxine is used as an adjunct to surgery and
congestive heart failure and arrhythmia; control fever, hypoglycemia, and fluid loss as necessary. Large doses of antithyroid drugs
radioiodine therapy. Generally, TSH is suppressed to <0.1 mU/L, and this usually requires a levothyroxine sodium dose of greater
(e.g., methimazole or propylthiouracil) followed in one to two hours by large doses of iodine may be given to inhibit synthesis and
than 2 mcg/kg/day
. However, in patients with high-risk tumors, the target level for TSH suppression may be <0.01 mU/L.
release of thyroid hormones. Glucocorticoids may be given to inhibit the conversion of T4 to T3. Plasmapheresis, charcoal
In the treatment of benign nodules and nontoxic multinodular goiter, TSH is generally suppressed to a higher target (e.g., 0.1 to either
hemoperfusion and exchange transfusion have been reserved for cases in which continued clinical deterioration occurs despite
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
conventional therapy. Because T4 is highly protein bound, very little drug will be removed by dialysis.
suppressed due to the risk of precipitating overt thyrotoxicosis (see CONTRAINDICATIONS, WARNINGS
DOSAGE AND ADMINISTRATION
– 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
The goal of replacement therapy is to achieve and maintain a clinical and biochemical euthyroid state. The goal of suppressive therapy
products are not recommended to treat this condition. Thyroid hormone products formulated for intravenous administration should
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
(levothyroxine sodium tablets, USP
) are round, color coded, scored and debossed with “SYNTHROID” on one side
). Hence, the following recommendations serve only as dosing guidelines. Dosing must be individualized and
and potency on the other side. They are supplied as follows:
adjustments made based on periodic assessment of the patient’s clinical response and laboratory parameters (see PRECAUTIONS,
SYNTHROID is administered as a single daily dose, preferably one-half to one-hour before breakfast. SYNTHROID should be taken
for bottles of 90
for bottles of 100
for bottles of 1000
for unit dose cartons of 100
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
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
Specific Patient Populations
Hypothyroidism in Adults and in Children in Whom Growth and Puberty are Complete (see WARNINGS and PRECAUTIONS,
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
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
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 patientwith 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- T
4 level is restored to the upper half of the normal range.
Store at 25°C (77°F); excursions permitted to 15°-30°C (59°-86°F) [see USP Controlled Room Temperature]. SYNTHROID tablets
Pediatric Dosage – Congenital or Acquired Hypothyroidism (see PRECAUTIONS, Laboratory Tests
should be protected from light and moisture.
(Nos. 4341, 4552, 5182, 6594, 6624, 9296, 7068, 3727, 7069, 7070, 7148, 7149)
In general, levothyroxine therapy should be instituted at full replacement doses as soon as possible. Delays in diagnosis andinstitution of therapy may have deleterious effects on the child’s intellectual and physical growth and development.
Undertreatment and overtreatment should be avoided (see PRECAUTIONS, Pediatric Use
SYNTHROID may be administered to infants and children who cannot swallow intact tablets by crushing the tablet and suspending
the freshly crushed tablet in a small amount (5-10 mL or 1-2 teaspoons) of water. This suspension can be administered by spoon or by
dropper. DO NOT STORE THE SUSPENSION.
Foods that decrease absorption of levothyroxine, such as soybean infant formula,
should not be used for administering levothyroxine sodium tablets (see PRECAUTIONS, Drug-Food Interactions
The recommended starting dose of levothyroxine sodium in newborn infants is 10-15 mcg/kg/day
. A lower starting dose
(e.g., 25 mcg/day) should be considered in infants at risk for cardiac failure, and the dose should be increased in 4-6 weeks as needed
based on clinical and laboratory response to treatment. In infants with very low (< 5 mcg/dL) or undetectable serum T4
concentrations, the recommended initial starting dose is 50 mcg/day
of levothyroxine sodium. Infants and Children
Levothyroxine therapy is usually initiated at full replacement doses, with the recommended dose per body weight decreasing with
age (see Table 3
). However, in children with chronic or severe hypothyroidism, an initial dose of 25 mcg/day
of levothyroxine sodium
is recommended with increments of 25 mcg every 2-4 weeks until the desired effect is achieved.
Hyperactivity in an older child can be minimized if the starting dose is one-fourth of the recommended full replacement dose,
and the dose is then increased on a weekly basis by an amount equal to one-fourth the full-recommended replacement dose until thefull recommended replacement dose is reached.
Table 3: Levothyroxine Sodium Dosing Guidelines for Pediatric Hypothyroidism
Daily Dose Per Kg Body Weighta
>12 years but growth and puberty incomplete
a The dose should be adjusted based on clinical response and laboratory parameters (see PRECAUTIONS, Laboratory Tests and
- Pregnancy may increase levothyroxine requirements (see PREGNANCY
- 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.
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HARMONIE UND VITALITÄT IM WECHSEL DES LEBENSEin ausgewogenes und gesundes Ernährungsverhalten bietet den Hauptschutz gegen vorzeitigen Vitalitätsmangel. Besonders im Wechsel des Lebens, dieser kann bereits schon mit 40 Jahren beginnen, wenn SIE erste Zeichen von häufiger Müdigkeit und abgekühlter Leidenschaft bemerkt, deuten solche Symptome meist auf eine ernährungsbedingte Fehlverso