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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.
Patients should be informed of the following information to aid in the safe and effective use of SYNTHROID:
- Notify your physician if you are allergic to any foods or medicines, are pregnant or intend to become pregnant, are breast-feeding or are taking any other medications, including prescription and over-the-counter preparations.
- Notify your physician of any other medical conditions you may have, particularly heart disease, diabetes, clotting disorders, and adrenal or pituitary gland problems. Your dose of medications used to control these other conditions may need to be adjusted while you are taking SYNTHROID. If you have diabetes, monitor your blood and/or urinary glucose levels as directed by your physician and immediately report any changes to your physician. If you are taking anticoagulants (blood thinners), your clotting status should be checked frequently.
- Use SYNTHROID only as prescribed by your physician. Do not discontinue or change the amount you take or how often you take it, unless directed to do so by your physician.
- The levothyroxine in SYNTHROID is intended to replace a hormone that is normally produced by your thyroid gland. Generally, replacement therapy is to be taken for life, except in cases of transient hypothyroidism, which is usually associated with an inflammation of the thyroid gland (thyroiditis).
- Take SYNTHROID as a single dose, preferably on an empty stomach, one-half to one hour before breakfast. Levothyroxine absorption is increased on an empty stomach.
- It may take several weeks before you notice an improvement in your symptoms.
- Notify your physician if you experience any of the following symptoms: rapid or irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives or skin rash, or any other unusual medical event.
- Notify your physician if you become pregnant while taking SYNTHROID. It is likely that your dose of SYNTHROID will need to be increased while you are pregnant.
- Notify your physician or dentist that you are taking SYNTHROID prior to any surgery.
- Partial hair loss may occur rarely during the first few months of SYNTHROID therapy, but this is usually temporary.
- SYNTHROID should not be used as a primary or adjunctive therapy in a weight control program.
- Keep SYNTHROID out of the reach of children. Store SYNTHROID away from heat, moisture, and light.
- Agents such as iron and calcium supplements and antacids can decrease the absorption of levothyroxine sodium tablets. Therefore, levothyroxine sodium tablets should not be administered within 4 hours of these agents.
Synthroid Drug Class
Synthroid is part of the drug class:
Synthroid and Lactation
Tell your doctor if you are breastfeeding or plan to breastfeed.
Synthroid has been detected in human breast milk. Because of the possibility for adverse reactions in nursing infants from Synthroid, a choice should be made whether to stop nursing or to stop use of this medication. The importance of the drug to the mother should be considered.
- Store at 25°C (77°F)
- Keep away from heat, moisture, and light
- Keep this and all medicines out of the reach of children
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
- Capsule, Liquid Filled
Therapeutic Class: Thyroid Supplement
Uses For Synthroid
Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine is also used to help decrease the size of enlarged thyroid glands (also called a goiter) and to treat thyroid cancer.
This medicine is available only with your doctor's prescription.
How is this medicine (Synthroid) best taken?
Use Synthroid as ordered by your doctor. Read all information given to you. Follow all instructions closely.
- Take on an empty stomach 30 minutes before breakfast.
- Some products may cause choking, gagging, or trouble swallowing. These products must be taken with a full glass of water. Ask your pharmacist if you need to take your product with a full glass of water.
- You may crush tablet and mix with 1 or 2 teaspoons (5 or 10 mL) of water.
- Do not take iron products, antacids that have aluminum or magnesium, or calcium carbonate, within 4 hours before or 4 hours after of this drug.
- Some other drugs may need to be taken at some other time than this medicine. If you take other drugs, check with your doctor or pharmacist to see if you need to take them at some other time than Synthroid (levothyroxine tablets).
- Some foods like soybean flour (infant formula) may change how this medicine works in your body. Talk with your doctor.
- If you drink grapefruit juice or eat grapefruit often, talk with your doctor.
- There is more than 1 brand of Synthroid. One brand cannot safely be used for the other. The doctor will tell you about any needed change.
- To gain the most benefit, do not miss doses.
- Keep taking this medicine as you have been told by your doctor or other health care provider, even if you feel well.
What do I do if I miss a dose?
- Take a missed dose as soon as you think about it.
- If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
- Do not take 2 doses at the same time or extra doses.
How do I store and/or throw out Synthroid?
- Store at room temperature.
- Protect from light.
- Store in a dry place. Do not store in a bathroom.
- Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
- Check with your pharmacist about how to throw out unused drugs.
Indications and Usage for Synthroid
Synthroid is indicated as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism.
Pituitary Thyrotropin (Thyroid‑Stimulating Hormone, TSH) Suppression
Synthroid is indicated as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.
- Limitations of Use:
- Synthroid is not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment with Synthroid may induce hyperthyroidism [see Warnings and Precautions(5.4)].
- Synthroid is not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.
Use in specific populations
Experience with levothyroxine use in pregnant women, including data from post-marketing studies, have not reported increased rates of major birth defects or miscarriages [see Data]. There are risks to the mother and fetus associated with untreated hypothyroidism in pregnancy. Since TSH levels may increase during pregnancy, TSH should be monitored and Synthroid dosage adjusted during pregnancy [see Clinical Considerations]. There are no animal studies conducted with levothyroxine during pregnancy. Synthroid should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated.
The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.
Disease-Associated Maternal and/or Embryo/Fetal Risk
Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre‑eclampsia, stillbirth, and premature delivery. Untreated maternal hypothyroidism may have an adverse effect on fetal neurocognitive development.
Dose Adjustments During Pregnancy and the Postpartum Period
Pregnancy may increase Synthroid requirements. Serum TSH levels should be monitored and the Synthroid dosage adjusted during pregnancy. Since postpartum TSH levels are similar to preconception values, the Synthroid dosage should return to the pre-pregnancy dose immediately after delivery [see Dosage and Administration (2.3)].
Levothyroxine is approved for use as a replacement therapy for hypothyroidism. There is a long experience of levothyroxine use in pregnant women, including data from post-marketing studies that have not reported increased rates of fetal malformations, miscarriages or other adverse maternal or fetal outcomes associated with levothyroxine use in pregnant women.
Limited published studies report that levothyroxine is present in human milk. However, there is insufficient information to determine the effects of levothyroxine on the breastfed infant and no available information on the effects of levothyroxine on milk production. Adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for Synthroid and any potential adverse effects on the breastfed infant from Synthroid or from the underlying maternal condition.
The initial dose of Synthroid varies with age and body weight. Dosing adjustments are based on an assessment of the individual patient's clinical and laboratory parameters [see Dosage and Administration (2.3, 2.4)].
In children in whom a diagnosis of permanent hypothyroidism has not been established, discontinue Synthroid administration for a trial period, but only after the child is at least 3 years of age. Obtain serum T4 and TSH levels at the end of the trial period, and use laboratory test results and clinical assessment to guide diagnosis and treatment, if warranted.
Congenital Hypothyroidism[See Dosage and Administration (2.3, 2.4)]
Rapid restoration of normal serum T4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on intellectual development as well as on overall physical growth and maturation. Therefore, initiate Synthroid therapy immediately upon diagnosis. Levothyroxine is generally continued for life in these patients.
Closely monitor infants during the first 2 weeks of Synthroid therapy for cardiac overload, arrhythmias, and aspiration from avid suckling.
Closely monitor patients to avoid undertreatment or overtreatment. Undertreatment may have deleterious effects on intellectual development and linear growth. Overtreatment is associated with craniosynostosis in infants, may adversely affect the tempo of brain maturation, and may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature.
Acquired Hypothyroidism in Pediatric Patients
Closely monitor patients to avoid undertreatment and overtreatment. Undertreatment may result in poor school performance due to impaired concentration and slowed mentation and in reduced adult height. Overtreatment may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature.
Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height. In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height.
Because of the increased prevalence of cardiovascular disease among the elderly, initiate Synthroid at less than the full replacement dose [see Warnings and Precautions (5.1) and Dosage and Administration (2.3)]. Atrial arrhythmias can occur in elderly patients. Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly.