Efavirenz and Toremifene interaction
Efavirenz and Toremifene: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Toremifene (Fareston) label · effective 2024-11-13
Drugs known to prolong the QT interval and strong CYP3A4 inhibitors should be avoided [see Warnings and Precautions (5.1) ] .
Coadministration with a strong CYP3A4 inducer may result in a relevant decrease in FARESTON exposure and should be avoided.
Coadministration with a strong CYP3A4 inhibitor can result in a relevant increase in FARESTON exposure and should be avoided.
Effect of Strong CYP3A4 Inhibitors on Toremifene In a study of 18 healthy subjects, 80 mg toremifene once daily coadministered with 200 mg of ketoconazole twice daily increased the toremifene Cmax and AUC by 1.4- and 2.9-fold, respectively.
The administration of FARESTON with agents that are strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, clarithromycin, atazanavir, indinavir, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, and voriconazole) increase the steady-state concentration in serum and should be avoided.
From the Efavirenz label · effective 2024-03-31
QT Prolonging Drugs There is limited information available on the potential for a pharmacodynamic interaction between efavirenz and drugs that prolong the QTc interval.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.