Metabolism of propafenone and lidocaine in combination in rat liver supernatant

Propafenone (Pro) and lidocaine (Lid) were incubated with rat liver supernatant and coenzyme factor. The competitive oxidations with each other were established. The original drug concentration of Pro and Lid were increased 0.7 and 0.5 times, respectively; and the metabolite dimethlglycinexylide (DGX) of Lid to be formed was decreased about 2/3 of that produced when administered alone. It was suggested that 1) they were metabolized by the same cytochrome P450 III A4 and the isozyme could be saturated, 2) the convulsive toxicity due to DGX will be decreased with its diminished formation, and 3) the combination of Lid and Pro would be beneficial for treatment of arrhythmias.