butabarbital will lessen the extent or outcome of levonorgestrel oral/ethinylestradiol/ferrous bisglycinate by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Carefully. The efficacy of hormonal contraceptives may be lowered.butabarbital will lower the level or outcome of levamlodipine by impacting hepatic/intestinal