Clinical assessment of cimetidine myelotoxicity.

After case reports of alleged cimetidine-induced neutropenia, we investigated the possibility that cimetidine might produce occult bone marrow injury by a mechanism other than idiosyncratic hypersensitivity. We performed hydrocortisone challenge tests to assess the bone marrow granulocyte reserves before, during, and after cimetidine administration. No decrease in marrow granulocyte reserves was associated with the administration of cimetidine. When cimetidine and lithium were given to volunteers, the granulocytosis normally associated with lithium was not diminished. Although a general myelosuppressive effect of cimetidine has been postulated by others, we found no evidence of such a phenomenon in this study. Idiosyncratic drug sensitivity is probably the mechanism of cimetidine-induced neutropenia.