Check Closely (1)pentobarbital will enhance the level or impact of clopidogrel by affecting hepatic/intestinal enzyme CYP3A4 metabolism.pentobarbital will decrease the extent or influence of guanfacine by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Closely. Sturdy or reasonable CYP3A4 inducers significantly reduce