Phenothiazines as Anti-Multi-Drug Resistant Tubercular Agents

L.      Amaral; M.      Martins; M.      Viveiros

doi:10.2174/187152607782110022

Abstract

Pulmonary tuberculosis (TB) has again become a global problem: it infects 2.2 billion people world-wide, caused the deaths of over 3 million last year and will produce over 8 million new cases of TB this coming year. Although effective therapy is widely available for antibiotic susceptible strains of Mycobacterium tuberculosis, current drugs are relatively useless against multi-drug resistant infections (MDRTB). Mortality is almost complete within two years regardless of therapy, and in the case of co-infection with HIV/AIDS, mortality is 100% within a few months of diagnosis especially the M. tuberculosis strain in XDRTB. As of the time of this writing no new effective anti-TB drugs have been made available by the pharmaceutical industry and XDRTB. Because TB is an intracellular infection of the non-killing macrophage of the lung, any agent that is to prove effective must have activity against MDRTB and XDRTB strains that have been phagocytosed by the human macrophage. This review intents to provide cogent in vitro, ex vivo and in vivo evidence that supports the use of a variety of commonly available phenothiazines for the therapy of MDRTB and XDRTB, especially when the prognosis of the infection is poor and the use of the recommend agents can take place along lines of “compassionate therapy”. In addition, we will describe the macrophage assay as indispensable when an agent is to be further studied for its effectiveness as an anti-TB drug. In vitro studies if not complemented by ex vivo studies will for the most part be dead-ended since few agents that have activity in vitro have any activity against phagocytosed M. tuberculosis.

Keywords: Thioridazine, inhibitors of efflux pumps, macrophages, enhanced killing, multi-drug resistant tuberculosis, intracellular infections, K+ transport, phagolysosome