pentobarbital will decrease the extent or impact of gefitinib by impacting hepatic/intestinal enzyme CYP3A4 metabolism.pentobarbital will lower the extent or impact of etoposide by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Watch.Doxycycline: Phenobarbital is shown to shorten the half-life of doxycycline for so long as 2 mon