Istradefylline 40 mg/day greater peak levels and AUC of CYP3A4 substrates in clinical trials. This effect wasn't observed with istradefylline twenty mg/day. Consider dose reduction of delicate CYP3A4 substrates.If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at Repeated i