Euthyrox Drug Interactions

Antidiabetic drugs: Levothyroxine (Euthyrox) may reduce the effect of antidiabetics. Therefore, it is necessary to check blood glucose levels frequently at the start of thyroid hormone therapy. If necessary, the dose of the antidiabetic drug has to be adjusted.
Coumarin derivatives: Levothyroxine (Euthyrox) may intensify the effect of anticoagulants as levothyroxine displaces anticoagulants from plasma protein bounds which may increase the risk of hemorrhage, 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 dose of the anticoagulant has to be adjusted.
Protease inhibitors: The doctor should be informed if the patient is taking protease inhibitors (e.g. ritonavir, indinavir, lopinavir) because these substances may influence the effect of levothyroxine (Euthyrox). Close monitoring of thyroid hormone parameters is recommended. If necessary, the levothyroxine (Euthyrox) dose has to be adjusted.
Phenytoin: Phenytoin may influence the effect of levothyroxine (Euthyrox) by displacing levothyroxine from plasma proteins resulting in an elevated fT4 and fT3 fraction. On the other hand, phenytoin increases the hepatic metabolization of levothyroxine. Close monitoring of thyroid hormone parameters is recommended.
Salicylates, dicoumarol, furosemide (in high doses of 250 mg), clofibrate: These drugs may intensify the effect of levothyroxine (Euthyrox). These drugs and other substances can displace levothyroxine (Euthyrox) from plasma proteins, resulting in an elevated fT4 fraction.
Proton Pump Inhibitors (PPIs): Possible decrease in the absorption of the thyroid hormones, due to the increase of the intragastric pH caused by the 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 (Euthyrox) 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 (Euthyrox). 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 (e.g. cholestyramine, cholestipol): Ion exchange resins inhibit the absorption of levothyroxine (Euthyrox). It is therefore recommended that levothyroxine (Euthyrox) be taken 4-5 hours before administration of ion exchange resins.
Aluminum containing drugs, iron-containing drugs, calcium salts: Aluminum-containing drugs (antacids, sucralfate), iron-containing drugs and calcium salts have been reported in literature as potentially decreasing the effect of levothyroxine. Drugs containing levothyroxine should therefore be administered at least 2 hours prior to the administration of aluminum-containing drugs, iron-containing drugs 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 unrecognized autonomy.
Sertraline, chloroquine/proguanil: These substances decrease the efficacy of levothyroxine (Euthyrox) and increase the serum TSH level.
Drugs leading to hepatic enzyme induction (e.g. barbiturates, carbamazepine): These substances can increase the hepatic clearance of levothyroxine (Euthyrox).
Estrogen: Women using estrogen-containing contraceptives or postmenopausal women under hormone-replacement therapy may have an increased need for levothyroxine (Euthyrox).
Soy products: Soy products may lower the uptake of levothyroxine (Euthyrox) from the intestine and therefore, an adjustment of the levothyroxine (Euthyrox) dose may be necessary, in particular at the beginning or after termination of nutrition with soy supplements.
Interaction 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).