Plasma concentrations of desethyl N-acetylprocainamide in patients treated with procainamide and N-acetylprocainamide.

We describe a method for routinely measuring plasma concentrations of procainamide (PA), N-acetylprocainamide (NAPA) and desethyl N-acetylprocainamide (NAPADE) by high-performance liquid chromatography (HPLC). The method has been used together with mass spectrometry of the appropriate chromatographic fraction to demonstrate that NAPADE is a metabolite of NAPA. In addition, comparison of NAPADE concentrations in the plasma of patients receiving PA and NAPA indicates that NAPA is not an intermediate for most of the NAPADE formed from PA. We propose that the principal route of NAPADE formation from PA occurs by initial dealkylation to form rho-amino-N-[2-(ethylamino)ethyl]benzamide (PADE), a hypothetical PA metabolite that has yet to be identified.U