Synthroid Levothyroxine Sodium: Side Effects, Uses, Dosage, Interactions, Warnings

Synthroid is a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body’s energy and metabolism. 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 ). Inadequate levothyroxine dosage will produce or fail to ameliorate the signs and symptoms of hypothyroidism.

Family history is very important when talking to these patients because there is a strong predisposition amongst family members in the primary setting to have another family member with hypothyroidism. One of the difficulties of the diagnosis of hypothyroidism is that the signs and symptoms are non-specific to the disease. So, in order to diagnose the disease accurately, given the non-specific symptoms, you must use the TSH level as a screening tool to assist in the family history and signs and symptoms that you have come across. Levothyroxine is the most commonly used treatment in this setting. Because of the increased prevalence of cardiovascular disease among the elderly, levothyroxine therapy should not be initiated at the full replacement dose (see WARNINGS, PRECAUTIONS , and DOSAGE AND ADMINISTRATION).

Concurrent use of sympathomimetics and SYNTHROID may increase the effects of sympathomimetics or thyroid hormone.
The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.
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 increases the response to oral anticoagulant therapy.

Patients with Underlying Cardiovascular Disease

There are certain foods that can interfere synthroid ovulation with the way SYNTHROID works, particularly we think about high-fiber foods that can interact with the absorption of thyroid medications. There are also certain vitamins and supplements that can interfere with the absorption of SYNTHROID. A levothyroxine product that is not therapeutically equivalent with SYNTHROID might not have the exact same effect on the patient’s TSH as SYNTHROID. The FDA has determined that drugs that are classified as therapeutically equivalent can be substituted with the full expectation that the substituted product will produce the same clinical effect and safety profile as the reference product. Levothroid is used for hashimoto’s disease, hypothyroidism, after thyroid removal, myxedema coma …

Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast.
The “optimal dose” was determined for each patient as that dosage of thyroxine being taken when the thyrotropin-releasing hormone (TRH) response was normal (ie, an increase in TSH of between 4.7 and 25 mIU/L).
If you become pregnant while taking Synthroid, do not stop taking the medicine without your doctor’s advice.
Unithroid is used for hashimoto’s disease, hypothyroidism, after thyroid removal, myxedema coma …

Antidepressant Therapy

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). 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 (T4) and L-triiodothyronine (T3), by the thyroid gland. Circulating serum T3 and T4 levels exert a feedback effect on both TRH and TSH secretion.

Levothyroxine

Notify your doctor if you experience serious side effects of Synthroid including rapid heartbeat, fluttering in your chest, or chest pain. Biochemical assessment incorporated measurement of serum TSH, T3, and T4. TSH lower limit of quantification was 0.2 mIU/L and upper limit of normal was 5.6 mIU/L, as indicated by the shaded area. Use the drop-down menu below to select your state and see the specific language required to prevent generic substitution. When prescribing SYNTHROID, protecting your script can ensure your patients receive SYNTHROID every time they refill their prescription. DAW codes are codes a pharmacy uses when filling your patient’s prescription.

Thyroid hormone synthesis and secretion is regulated by the hypothalamic-pituitary-thyroid axis.
Plasmapheresis, charcoal hemoperfusion and exchange transfusion have been reserved for cases in which continued clinical deterioration occurs despite conventional therapy.
These consequences include, among others, effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism.

Specific Patient Populations

The initial dose of levothyroxine varies with age and body weight (see DOSAGE AND ADMINISTRATION – Table 3). Dosing adjustments are based on an assessment of the individual patient’s clinical and laboratory parameters (see PRECAUTIONS – Laboratory Tests). Consumption of certain foods may affect levothyroxine absorption thereby necessitating adjustments in dosing. Soybean flour (infant formula), cotton seed meal, walnuts, and dietary fiber may bind and decrease the absorption of levothyroxine sodium from the GI tract. The therapeutic effects of digitalis glycosides may be reduced by levothyroxine. Serum digitalis glycoside levels may be decreased when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides (see Table 2).

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 recommended starting daily dosage of SYNTHROID in pediatric patients with primary, secondary, or tertiary hypothyroidism is based on body weight and changes with age as described in Table 2. Titrate the dosage (every 2 weeks) as needed based on serum TSH or free- T4 until the patient is euthyroid see Important Considerations For Dosing. For secondary or tertiary hypothyroidism, serum TSH is not a reliable measure of SYNTHROID dosage adequacy and should not be used to monitor therapy. Use the serum free-T4 level to titrate SYNTHROID dosing until the patient is clinically euthyroid and the serum free-T4 level is restored to the upper half of the normal range see Recommended Dosage And Titration.

It is not indicated for the suppression of benign thyroid nodules, or for non-toxic defuse goiter in iodine-sufficient patients. It is also not indicated for the treatment of hypothyroidism during the recovery phase of subacute thyroiditis. There are safety considerations as SYNTHROID should not be used for treatment of obesity or for weight loss.

Acute Adrenal Crisis In Patients With Concomitant Adrenal Insufficiency

SYNTHROID is indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Synthroid is prescribed in tablets that range from 25 to 300 mcg in strength and is usually taken once a day with a full glass of water (about 8 ounces) 30 to 60 minutes before breakfast for best adsorption into the body. Children can take the medicine if the tablet is crushed and put into about 1 to 2 teaspoons of water; do not store or delay giving this crushed pill suspension. Doctors often may have to slowly increase the dose; patients should not increase or decrease this medication themselves. Because some preparations of the drug may contain iodine or lactose, patients should tell their doctors about such allergies or reactions to these components.