Istradefylline forty mg/working day elevated peak levels and AUC of CYP3A4 substrates in clinical trials. This effect wasn't observed with istradefylline 20 mg/day. Consider dose reduction of delicate CYP3A4 substrates.viloxazine will increase the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Keep