Abstract

This chapter deals with the classification and mechanisms of drug resistance in tuberculosis, from mono-resistant to extensive drug resistance (XDR) strains. Resistance can be classified as “new cases” for patients never treated before (or treated for less than a month) with antituberculosis drugs and infected by an already drug resistant strain, and “previously treated cases”. There are multiple factors associated to drug resistance but they can be grouped in three basic categories: clinical, biological and social factors. Clinical factors include, among others, inadequate treatment regimens (wrong drugs, wrong doses), using drugs of unproven quality, drug shortages, and treatment with weak regimens by private physicians. Biological factors can include factors both the host and from the mycobacteria: being infected with an already resistant strain or host immunosuppression. Social factors include residing in areas with high rates of DR-TB, extreme poverty and lack of social support, illiteracy, poorly structured and supported TB control programs and lack of political compromise.