Quinidine-induced neutropenia: report of a case with drug-dependent inhibition of granulocyte colony generation.

We describe a case of quinidine-induced agranulocytosis in which in vitro marrow culture studies suggested immune inhibition of committed human granulocyte-macrophage progenitors (CFU-GM). Autologous, but not allogeneic, inhibition of CFU-GM was seen with 'acute' serum from the patient in the presence of quinidine but not other drugs. Cytotoxic antibodies to mature granulocytes were not found. These studies provide a novel mechanism for drug-induced neutropenia and suggest that a battery of in vitro assays of progenitor and of mature granulocyte cytotoxicity might identify offending agents in suspected drug-induced neutropenias.