In vitro antibacterial activity of drugs against human intestinal anaerobic bacteria.

The in vitro antibacterial activity, against the major groups of anaerobic fecal bacteria, of a series of drugs was examined by an agar diffusion test and the minimum inhibitory concentration (MIC) test. Only the phenothiazines and amitriptyline showed any marked antibacterial activity, the MIC's being in the 40-640-mu-g/ml range. It is suggested that the detergent nature of the molecules of these drugs in aqueous solution is responsible for the observed antibacterial activity.