How the interaction occurs:
Carbamazepine, dexamethasone, phenobarbital, phenytoin, rifabutin, rifampin, and St. John's wort may speed up how quickly your liver processes tamoxifen or toremifene. Toremifene may speed up how quickly your body processes phenytoin.
What might happen:
The amount of tamoxifen or toremifene in your blood may decrease and it may not work as well. If you are taking phenytoin, the amount of phenytoin in your blood may also decrease and it may not work as well.
What you should do about this interaction:
Make sure your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together or if you have taken carbamazepine, dexamethasone, phenobarbital, phenytoin, rifabutin, rifampin, or St. John's wort in the previous two weeks, or if you stop taking St. John's wort. Your doctor may want to adjust your medicines. If you are taking phenytoin with toremifene, your doctor may want to check your phenytoin levels.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Nolvadex (tamoxifen citrate) US prescribing information. AstraZeneca Pharmaceuticals LP March, 2006.
2.Fareston (toremifene citrate) US prescribing information. GTx, Inc. March, 2011.
3.Anttila M, Laakso S, Nylanden P, Sotaniemi EA. Pharmacokinetics of the novel antiestrogenic agent toremifene in subjects with altered liver and kidney function. Clin Pharmacol Ther 1995 Jun;57(6):628-35.
4.Kivisto KT, Villikka K, Nyman L, Anttila M, Neuvonen PJ. Tamoxifen and toremifene concentrations in plasma are greatly decreased by rifampin. Clin Pharmacol Ther 1998 Dec;64(6):648-54.
5.US Food and Drug Administration (FDA). Drug Development and Drug Interactions: Table of Substrates, Inhibitors and Inducers. Available at: http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/D rugInteractionsLabeling/ucm093664.htm. Updated 08/05/2011.