pentobarbital decreases amounts of elvitegravir/cobicistat/emtricitabine/tenofovir DF by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Might cause loss of virologic response and doable resistance.pentobarbital will decrease the extent or impact of tamoxifen by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Ca