- Use of CYP3A4 enzyme-inducing anticonvulsants phenytoin and strong CYP3A4 inducers is not allowed and patients must be off any of these exclusionary products for > 2 weeks from day 1. The use of strong CYP3A4 inducers (e.g., rifampin, phenytoin, carbamazepine, rifabutin, rifapentine, phenobarbital, St. John's wort) should not be used during the trial. If possible, substitute non-enzyme inducing therapies at least 2 weeks prior to treatment day 1.