one, seven.two) ]. Threats of Concomitant Use or Discontinuation of Cytochrome P450 2D6 Inhibitors The concomitant use of Promethazine with Codeine Oral Solution with all cytochrome P450 2D6 inhibitors (eg., amiodarone, quinidine) may perhaps cause a rise in codeine plasma concentrations in addition to a decrease in active metabolite morphine plasm