Drug-induced inhibition of myeloid colony growth: protective effect of colony-stimulating factor.

The effect of some potentially myelotoxic drugs on the growth of colony-forming cells in mouse marrow in vitro was examined. Among the drugs tested chloramphenicol, thiamphenicol, and chlorpromazine were inhibitory in therapeutic concentrations, a finding consistent with the common occurrence of a dose-dependent leukopenia from these drugs. The degree of drug-induced inhibition of colony growth was inversely proportional to the concentration of colony-stimulating factor in the medium. It is postulated that the concentration of colony-stimulating factor in the cell milieu in vivo may play a significnat role in determining the occurrence or degree of leukopenia from thses drugs.