- Concomitant use of known strong (eg. phenobarbital, phenytoin, rifampicin, rifabutin, rifapentine, carbamazepine, and St John's Wort ) or moderate CYP3A inducers (eg. bosentan, modafinil). The required washout period prior to starting olaparib is 5 weeks for phenobarbital and 3 weeks for other agents.