Istradefylline forty mg/working day improved peak levels and AUC of CYP3A4 substrates in clinical trials. This effect was not observed with istradefylline 20 mg/day. Consider dose reduction of delicate CYP3A4 substrates.If coadministration of CYP3A4 inhibitors with fentanyl is essential, keep track of patients for respiratory depression and sedatio