- Use of any known inducers or inhibitors of CYP2C9 within 30 days (or at least 5 half-lives, whichever is shorter) prior to enrollment. Drugs that are inhibitors or inducers of CYP2C9 are also excluded throughout Periods 1 and 2. Drugs that are known to increase the hypoprothrombinemic effect of warfarin are excluded prior to enrollment and throughout Periods 1 and 2.