1, 7.two) ]. Hazards of Concomitant Use or Discontinuation of Cytochrome P450 2D6 Inhibitors The concomitant use of Promethazine with Codeine Oral Resolution with all cytochrome P450 2D6 inhibitors (eg., amiodarone, quinidine) could result in a rise in codeine plasma concentrations in addition to a minimize in active metabolite morphine plasma focu