Cimetidine-induced neutropenia: a possible dose-related phenomenon.

Neutropenia associated with high-dose cimetidine therapy developed in a patient in whom earlier therapy, as well as rechallenge with low-dose cimetidine, did not result in neutropenia. As other factors cannot be implicated, a dose-related toxicity of cimetidine appears likely. Although the mechanism of cimetidine-induced neutropenia is unknown, it may involve the previously demonstrated ability of histamine H2 receptor antagonists to block the histamine-induced initiation of DNA synthesis in bone marrow stem cells.