Background: Plasma Inhibitory Activity Assay (Plasma Bactericidal Assay) is an assay that gives quantitative estimates of effectiveness of the bactericidal effect in patients who are on anti tuberculosis therapy .The assay involves the use of pre-isolated organisms and blood (plasma) from the same patient on treatment. Minimum Inhibitory Concentration is the minimum concentration of drug that will kill/inhibit the growth of micro-organism. This is the quantitative estimation of Drug Susceptibility of an organism to tested drugs. It involves the use of pre-isolated organism from the patient before the start of treatment. Study aim: Was to determine and compare the Tuberculosis drug activity (TDA) and Minimum Inhibitory Concentration (MIC) of second line anti TB drugs among MDR-TB patients admitted at KNTH. Methodology: The study was cross-sectional study. It involved participants who were diagnosed and confirmed to have MDR-TB, who agreed to sign the consent form. Prior to the start of MDR-TB treatment sputum was collected from each participant, processed and cultured on liquid and solid media. Three weeks after the initiation of MDR-TB treatment, blood was collected from each participant and plasma separated. Plasma was used to test the pre-isolated organisms in a liquid culture and TTP was recorded. DST results (MIC) was done on trek MIC plates (Sensititre® MYCOTB MIC plates) using the pre-isolated organism from solid media. TDA (calculated from TTP) were correlated with MIC. Results: The mean TDA among 14 participants was 2.19±0.62 for those who were treated with Capreomycin, ofloxacilin, ethionamide, and pyrazinamide. Among the 14 participants, 7 participants were treated with Kanamycin, ethionamide, levofloxacin, pyrazinamide and cycloserine later showed mean TDA of 2.19±1.0. MIC and TDA showed inverse relationship.Since TDA>2 none of the participants showed resistance to treatment. Conlusion: Drug activity was found to correlate with Minimum inhibitory concentration during treatment of pulmonary TB. This indicates that these markers have a role and should be used in monitoring the treatment outcome which includes prediction of drug resistance in early stages of treatment. Recommendation: We recommend that, this method to be implemented and used in assessing the effectiveness of treatment and determine resistance among MDR-TB patients on therapy.