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Author: Admin | 2025-04-28
Concurrent use of sympathomimetics and levothyroxine sodium tablets may increase the effects of sympathomimetics or thyroid hormone. Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease. 7.8 Tyrosine-Kinase Inhibitors Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism. Closely monitor TSH levels in such patients. 7.9 Drug-Food Interactions Consumption of certain foods may affect levothyroxine sodium tablets 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 levothyroxine sodium tablets from the gastrointestinal tract. Grapefruit juice may delay the absorption of levothyroxine and reduce its bioavailability. 7.10 Drug-Laboratory Test Interactions Consider changes in TBG concentration when interpreting T4 and T3 values. Measure and evaluate unbound (free) hormone and/or determine the free-T4 index (FT4I) in this circumstance. Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentration. Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens, and corticosteroids decrease TBG concentration. Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000. Biotin supplementation is known to interfere with thyroid hormone immunoassays that are based on a biotin and streptavidin interaction, which may result in erroneous thyroid hormone test results. Stop biotin and biotin-containing supplements for at least 2 days prior to thyroid testing. 8 Use In Specific Populations Pregnancy may require the use of higher doses of levothyroxine sodium tablets. (2.3, 8.1) 8.1 Pregnancy The clinical experience, including data from postmarketing studies, in pregnant women treated with oral levothyroxine to maintain euthyroid state have not reported increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes. 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 levothyroxine sodium tablets dosage adjusted during pregnancy (see Clinical Considerations). Animal reproductive studies have not been conducted with levothyroxine sodium. Levothyroxine sodium tablets 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. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in
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