pentobarbital will reduce the level or result of fosamprenavir by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Keep an eye on.pentobarbital will reduce the extent or impact of irinotecan by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Watch.fentanyl transmucosal and pentobarbital each increase sedation.