Levothyroxine: Uses, Dosage, Side Effects

Soybean flour (infant formula), cotton seed meal, walnuts, and dietary fiber may bind and decrease the absorption of levothyroxine sodium from the GI tract. Addition of SYNTHROID therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control, especially when thyroid therapy is started, changed, or discontinued see Warnings and Precautions (5.5). Stop biotin and biotin-containing supplements for at least 2 days before assessing TSH and/or T4 levels see Drug Interactions (7.10). Do not administer in foods that decrease absorption of SYNTHROID, such as soybean-based infant formula see Drug Interactions (7.9). SYNTHROID may reduce the therapeutic effects of digitalis glycosides.

PRECAUTIONS

Thyroid hormones do not readily cross the placental barrier see Use in Specific Populations (8.1). Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins see DRUG INTERACTIONS. Thyroid hormones do not readily cross the placental barrier see Use In Specific Populations. Administration of thyroid hormone in doses higher than those produced physiologically by the gland results in suppression of the production of endogenous hormone. 131I uptake is determined before and after the administration of the exogenous hormone.

• This is important because the amount of medicine you need is very precise.
• Levothyroxine sodium is contraindicated if the serum TSH is already suppressed due to the risk of precipitating overt thyrotoxicosis (see CONTRAINDICATIONS, WARNINGS and PRECAUTIONS).
• Do not administer in foods that decrease absorption of SYNTHROID, such as soybean-based infant formula.
• 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.
• 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.

1 General Administration Information

• This initial dose is followed by daily supplements of 100 to 200 mcg given IV.
• Sometimes it is not safe to use certain medicines at the same time.
• However, you may not be able to take this medicine if you have certain medical conditions.
• Tell your doctor about all your current medicines and any medicine you start or stop using.
• Although thyroid hormones are excreted only minimally in human milk, caution should be exercised when SYNTHROID is administered to a nursing woman.

The signs and symptoms of overdosage are those of hyperthyroidism see Warnings and Precautions (5) and Adverse Reactions (6). Seizures occurred in a 3-year-old child ingesting 3.6 mg of levothyroxine. Titrate the dose of SYNTHROID carefully and monitor response to titration to avoid these effects see Dosage and Administration (2.4). Consider the potential for food or drug interactions and adjust the administration or dosage of SYNTHROID as needed see Dosage and Administration (2.1), Drug Interactions (7.1), and Clinical Pharmacology (12.3). The signs and synthroid lpr symptoms of overdosage are those of hyperthyroidism see WARNINGS AND PRECAUTIONS and Adverse Reactions.

Many drugs can inhibit Synthroid’s adsorption by the body; other medications may increase or decrease its effectiveness once it is adsorbed. Providing a complete list of medications to the doctor will help with getting the correct dose established for each individual patient. If you become pregnant while taking Synthroid, do not stop taking the medicine without your doctor’s advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Thyroid hormones should be administered cautiously to patients in whom there is strong suspicion of thyroid gland autonomy, in view of the fact that the exogenous hormone effects will be additive to the endogenous source.

Precautions for Synthroid

Adequate therapy usually results in normal TSH and T4 levels after 2 to 3 weeks of therapy. 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). In order for Synthroid to be effective, it should always be taken the same way every day. This is important because the amount of medicine you need is very precise. And even the way you take Synthroid can affect how much medicine your body is getting.

If the serum TSH is already suppressed, levothyroxine sodium should not be administered (see CONTRAINDICATIONS). Consumption of certain foods may affect SYNTHROID absorption thereby necessitating adjustments in dosing see Dosage and Administration (2.1). Soybean flour, cottonseed meal, walnuts, and dietary fiber may bind and decrease the absorption of SYNTHROID from the gastrointestinal tract. Grapefruit juice may delay the absorption of levothyroxine and reduce its bioavailability. If so, advise them to stop biotin supplementation at least 2 days before assessing TSH and/or T4 levels see Dosage and Administration (2.4) and Drug Interactions (7.10).

This list is not complete and many other drugs may interact with levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of this medicine, especially if you are taking any other weight-loss medications or appetite suppressants. You may not be able to use levothyroxine if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder or any heart problems such as a recent heart attack.

Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast. Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use levothyroxine only for the indication prescribed. You may be more likely to have a broken bone while using levothyroxine.

• The patient should be monitored closely to avoid undertreatment and overtreatment.
• 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.
• Patients with diabetes mellitus may require upward adjustments of their antidiabetic therapeutic regimens when treated with levothyroxine (see PRECAUTIONS – Drug Interactions).
• Prothrombin time should be closely monitored to permit appropriate and timely dosage adjustments (see Table 2).
• Intramuscular administration is not advisable because of reported poor absorption.
• SYNTHROID® (levothyroxine sodium) tablets, for oral use is a prescription, man-made thyroid hormone that is used to treat a condition called hypothyroidism in adults and children, including infants.

SYNTHROID should be taken at least 4 hours apart from drugs that are known to interfere with its absorption (see PRECAUTIONS – Drug Interactions). Levothyroxine sodium should be reduced in dose or temporarily discontinued if signs or symptoms of overdosage occur. 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. 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.

We anticipate reposting the images once we are able identify and filter out images that do not match the information provided in the drug labels. Foods containing soy and cottonseed meal can make Synthroid less effective. Walnuts, grapefruit juice, and dietary fiber can also make Synthroid less effective.