Procainamide-induced agranulocytosis with reversible myeloid sensitivity.

A 56-year-old man developed procainamide-induced agranulocytosis. Bone marrow aspiration showed the absence of myeloid elements beyond the promyelocyte stage. Procainamide at therapeutic concentrations in vitro depressed bone marrow granulocyte-macrophage colonies (CFUc) while CFUc growth was normal in the absence of drug. Following the patient's recovery, CFUc growth was no longer suppressed by procainamide in vitro. The observations in this patient showing reversible sensitivity to drug contrast with those on other patients with drug-induced agranulocytosis that show persistent marrow injury or drug sensitivity despite clinical recovery.