The antibacterial effect of selected phenothiazines and thioxanthenes on slow-growing mycobacteria.

The aim of the present investigation was to illustrate the antibacterial effect of various phenothiazine and thioxanthene derivatives on mycobacteria in vitro. It was demonstrated that clopenthixol is about twice as potent as chlorpromazine (CPZ) and levomepromazine-maleate is about half as potent as CPZ, measured by the inhibitory effect on the growth of the mycobacterial strains. Measured in the same way the stereoisomeric compounds of flupenthixol are shown to be more potent than the stereo-isomeric compounds of clopenthixol and chlorprothixen. The two last-named compounds are equal in potency. The stereo-isomeric analogs of the thioxanthene derivatives are equal in antibacterial potency against the slow-growing mycobacteria. The mycobacterial strains investigated show no difference in sensitivity between the cis (Z)--and and trans (E)--compounds of the thioxanthenes. It seems particularly promising that also the more resistant mycobacteria other than Mycobacterium tuberculosis, e.g. M. avium and M. intracellulare, are sensitive in the concentration range investigated. Considered as a whole, these results might be a stimulus to investigate the antimicrobial effect of the thioxanthenes in vivo.