Euthyrox Drug Interactions

Protease inhibitors: Protease inhibitors (e.g. ritonavir, indinavir, lopinavir) may influence the effect of levothyroxine. Close monitoring of thyroid hormone parameters is recommended. If necessary, the levothyroxine dose has to be adjusted.
Phenytoin: Phenytoin may influence the effect of levothyroxine by displacing levothyroxine from plasma proteins resulting in an elevated fT4 and fT3 fraction. On the other hand, phenytoin increases the hepatic metabolisation of levothyroxine. Close monitoring of thyroid hormone parameters is recommended.
Influence of levothyroxine on other medicinal products: Anti-diabetic medicinal products: Levothyroxine may reduce the effect of anti-diabetics. Therefore, it is necessary to check blood glucose levels frequently at the start of thyroid hormone therapy. If necessary, the anti-diabetic dose has to be adjusted.
Coumarin derivates: Levothyroxine may intensify the effect of anticoagulants by displacing them from plasma protein bounds, which may increase the risk of haemorrhage e.g. CNS or gastrointestinal bleeding, especially in elderly patients. Therefore, it is necessary to check the coagulation parameters regularly at the start of and during concomitant therapy. If necessary, the anticoagulant dose has to be adjusted.
The following medicinal products intensify the effect of levothyroxine: Salicylates, dicumarol, furosemide, clofibrate: Salicylates, dicumarol, furosemide in high doses (250 mg), clofibrate and other substances can displace levothyroxine from plasma proteins, resulting in an elevated fT4 fraction.
The following medicinal products may reduce the effect of levothyroxine: Proton pump inhibitors (PPIs): Possible decrease in the absorption of the thyroid hormones, due to the increase of the intragastric pH caused by PPIs. Regular biological and clinical monitoring, with a possible increase in the dose of thyroid hormones.
Orlistat: Hypothyroidism and / or reduced control of hypothyroidism may occur when orlistat and levothyroxine are taken at the same time. This could be due to a decreased absorption of iodine salts and / or levothyroxine.
Sevelamer: Sevelamer may decrease levothyroxine absorption. Therefore, it is recommended that patients are monitored for changes in thyroid function at the start or end of concomitant treatment. If necessary, the levothyroxine dose has to be adjusted.
Tyrosine kinase inhibitors: Tyrosine kinase inhibitors (e.g. imatinib, sunitinib) may decrease the efficacy of levothyroxine. Therefore, it is recommended that patients are monitored for changes in thyroid function at the start or end of concomitant treatment. If necessary, the levothyroxine dose has to be adjusted.
Ion exchange resins: Ion exchange resins (e.g. cholestyramine or cholestipol) inhibit the absorption of levothyroxine. It is therefore recommended that levothyroxine be taken 4 - 5 hours before administration of such agents.
Aluminium, iron and calcium salts: Aluminium-containing medicinal products (antacids, sucralfate) have been reported in literature as potentially decreasing the effect of levothyroxine. It is therefore recommended that levothyroxine be administered at least 2 hours prior to the administration of aluminium-containing medicinal products. The same applies to medicinal products containing iron and calcium salts.
Propylthiouracil, glucocorticoids, beta-sympatholytics, and iodine-containing contrast media: These substances inhibit the peripheral conversion of T4 to T3.
Amiodarone: This substance inhibits the peripheral conversion of T4 to T3.
Due to its high iodine content amiodarone can trigger hyperthyroidism as well as hypothyroidism. Particular caution is advised in the case of nodular goiter with possibly unrecognised autonomy.
Sertraline, chloroquine/proguanil: These substances decrease the efficacy of levothyroxine and increase the serum TSH level.
Medicinal products leading to hepatic enzyme induction (e.g. barbiturates, carbamazepine): These substances can increase the hepatic clearance of levothyroxine.
Oestrogens: Women using oestrogen-containing contraceptives or postmenopausal women under hormone-replacement therapy may have an increased need for levothyroxine.
Interaction with food: Soy containing compounds: Soy containing compounds can decrease the intestinal absorption of levothyroxine. Therefore, a dosage adjustment of Euthyrox may be necessary, in particular at the beginning or after termination of nutrition with soy supplements.
Interference with laboratory test: Biotin may interfere with thyroid immunoassays that are based on a biotin/streptavidin interaction, leading to either falsely decreased or falsely increased test results (see Precautions).