Isoniazid-induced pure red cell aplasia.

The clinical courses of four individuals with pure red cell aplasia associated with isoniazid use are described. Erythroblastopenia in these individuals resolved following cessation of this antituberculous therapy. A clonal assay system that quantitates erythroid precursor cells was used to investigate the pathogenesis of the red cell aplasia in three of the patients. Using this technique, however, we were unsuccessful in demonstrating an inhibitory effect of acute phase serum, isoniazid or a combination of the two on erythroid colony formation. We conclude that isoniazid usage alone appears to be associated with a readily reversible form of acquired pure red cell aplasia. In addition, the results of our in vitro studies emphasize the limitations of bone marrow culture systems when used to implicate offending drugs in the production of drug related cytopenias.