The purpose of using anti-tubercular drug therapy in combination is:

Ans. c (To reduce the possibility of drug resistance). (Ref. KDT, Pharmacology, 6th ed., p 739)PRINCIPLES OF ANTI-TB CHEMOTHERAPY# Multiple drugs used in combination will reduce the possibility of selecting drug-resistant strains and hence chances of relapse. Among the first-line drugs, pyrazinamide, being active in an acidic environment, takes care of the persistent intracellular bacilli.# In general, regimens that are adequate for treating pulmonary TB are also effective for treating extrapulmonary TB. The problem lies in deciding on the appropriate duration of treatment. By WHO criteria, all caries spine cases should be treated for a minimum of 6 months.# For the purpose of rationalizing and initiating treatment, WHO categorizes TB patients into four categories depending upon clinical severity and priority.# Treatment in a category is divided into initial, intensive, and subsequent continuation phases.# The intensive phase comprises maximum number of drugs given daily (preferably under supervision) and is intended to bring about rapid clinical amelioration and achieve non-infectivity. Treatment is then continued with 2 or 3 drugs given daily or intermittently to eliminate residual bacilli and prevent relapse.# The initial intensive phase drugs may need to be maintained into the continuation phase. It is recommended that for infants and children with miliary TB or bone and joint TB treatment should last at least 12 months. For adults with these forms of extrapulmonary TB, the patient's response to therapy should be monitored closely. If response is slow or inadequate, treatment may be prolonged on a case-by-case basis.# Treatment in HIV-positive individuals:# The treatment regimens as outlined above are also effective in the presence of HIV infection. Unfortunately, complex interactions between rifampicin and antiretroviral drugs may force withdrawal of conventional regimens. Rifabutin has been used as an alternative to rifampicin in such situations.