Isoniazid-induced pure red cell aplasia.

Pure red blood cell aplasia (PRCA) is an extremely rare side effect of isoniazid (INH). We have encountered 2 patients who developed anemia caused by PRCA. One was receiving INH preventive therapy and the other was being treated with INH and rifampin. On withdrawal of INH, the anemia responded rapidly. For unexplained anemia during INH therapy, PRCA should be considered as a cause.