Vol. 2, Issue 12, Part A (2016)

Abstract
Minimum Bactericidal Concentration (MBC) test is the one most frequently used to quantitate bactericidal potency. The MBC values can then be compared with concentrations attainable in blood and tissues to achieve a basis for considerations as to whether the bactericidal effect can be anticipated in the clinical situation. Also the rate of killing can be assessed thus giving a dynamic picture of drug action. It also helps to confirm the results of synergism obtained by checkerboard studies and helps to determine the potential for the antibiotic combination to demonstrate enhanced bactericidal activity as compared to each of the individual drugs. With the increasing prevalence of Mycobacterial infections, the development of new antimycobacterial agents and strategies for treating Mycobacterial infections is of paramount importance, As drug development is a long and expensive process, it becomes predominant to reexamine drugs that were formerly deemed effective against TB and increase the permeability of the Mycobacterial cell wall. One such drug is Isoxyl (ISO). ISO is an old drug, used for the clinical treatment of TB in 1960’s. The log phase, sometimes called the logarithmic phase, is a period characterized by cell doubling. The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited, doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with each consecutive time period. The stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. In this study we have evaluated bactericidal activity of INH and RF alone and in combination with ISO by time kill kinetic study in vitro against log phase and stationary phase culture against standard strain of Mycobacterium tuberculosis. Synergistic bactericidal effects between ISO & INH and RF& ISO were evident in exponential phase cultures but were absent in the stationery phase cultures. The ability of ISO particularly at their higher concentrations to the increase the bactericidal activity of INH or RF was lost at the culture changed from exponential phase to stationery phase. The result of the present study suggests that ISO could be particularly useful in the first few days of treatment of pulmonary TB, when the majority of the bacterial population is actively multiplying in cavity walls. ISO is expected to have fairly high bactericidal activity at the start of treatment. The low level of bactericidal activity on stationery phase cultures suggest that, though they would still continue to inhibit growth, ISO would not be effective in shortening the duration of treatment. The results shown here with the combined medicament, ISO was in our opinion not unsatisfactory in bactericidal activity.