[Effect of cimetidine on human granulopoietic stem cells. In vitro study in 31 patients].

We studied the action of cimetidine at various concentrations on human hematopoeitic colony and cluster forming cells "in vitro" (CFUc). Bone marrow samples obtained from 31 patients with various hematological and neoplastic diseases were cultured in semisolid agar. When cimetidine was added to cultures there was a reduction of colony and macrocluster formation. At the concentration used in our study (20 micrograms/ml, 30 micrograms/ml, 40 micrograms/ml) these effects were not dose-related. We did not find any significant reduction of microcluster formation. These results are relevant with the hypothesis that histamine H2 receptors antagonists may have an inhibiting action on bone marrow CFUc proliferation. They point out the need for hematological surveillance during long-term cimetidine therapy.