Drug-Drug

• Lapatinib inhibits CYP3A4, CYP28 and P-glycoprotein; concurrent use of drugs, which are substrates for these enzyme should be undertaken with caution.

• May ↑ effects of midazolam , paclitaxel , and digoxin .

• Concurrent use of strong CYP3A4 inhibitors including ketoconazole , itraconazole , clarithromycin , atazanavir , indinavir , nefazodone , nelfinavir , ritonavir , saquinavir , telithromycin , and voriconazole may ↑ blood levels and the risk of toxicity. Concurrent use should be avoided, but if necessary, dose of lapatinib should be ↓.

• Concurrent use of strong CYP3A4 inducers including dexamethasone , phenytoin , carbamazepine , rifampin , rifabutin , rifapentin , and phenobarbital may ↓ blood levels and effectiveness. Concurrent use should be avoided, but if necessary, dose of lapatinib should be ↑.

Drug-Natural Products
Concurrent use of St. John's wort may ↓ blood levels and effectiveness. Concurrent use should be avoided, but if necessary dose of lapatinib should be ↑and should be avoided.

Drug-Food
Concurrent grapefruit juice may ↑ blood levels and the risk of toxicity and should be avoided.