N-Acetylprocainamide is a class III antiarrhythmic, which blocks K⁺ channels. IC50 & Target: K⁺ channel^[1] In Vitro: N-Acetylprocainamide is a K⁺ blocker. N-Acetylprocainamide decreases the tensions induced by K⁺ and methacholine. The pIC₅₀ values for N-acetylprocainamide against the contractions induced by 0.3 and 1 μM methacholine are 2.80 ± 0.03 and 2.65 ± 0.02, respectively. And such a relaxant effect of N-Acetylprocainamide is inhibited by K⁺ channel blockers^[1]. N-Acetylprocainamide shows no effect on Na⁺ absorption or Cl^- secretion^[2].