butabarbital will decrease the level or impact of sulfamethoxazole by influencing hepatic enzyme CYP2C9/ten metabolism. Minor/Importance Not known.butabarbital will reduce the level or impact of carvedilol by impacting hepatic enzyme CYP2C9/ten metabolism. Use Caution/Watch.butabarbital will lessen the extent or effect of levoketoconazole by influe