1, 7.two) ]. Pitfalls of Concomitant Use or Discontinuation of Cytochrome P450 2D6 Inhibitors The concomitant usage of Promethazine with Codeine Oral Answer with all cytochrome P450 2D6 inhibitors (eg., amiodarone, quinidine) may bring about an increase in codeine plasma concentrations and a reduce in Lively metabolite morphine plasma focus which c