Predictors of Treatment Success for Multidrug Resistant Tuberculosis

After decades of relatively little attention, the field of tuberculosis (TB) research has drawn much attention in recent years. New anti-TB drugs, those already commercially available and others still in the development pipeline, are among the primary drivers of active research, along with commitments from governmental and non-governmental entities for the global eradication of TB. However, many issues remain to be solved, requiring additional attention, resources, and cooperation. One of the urgent issues regarding TB is multidrug-resistant TB (MDR-TB). MDR-TB is defined as Mycobacterium tuberculosis that is resistant to at least isoniazid and rifampin. In 2015, there were estimated 480,000 new cases of MDR-TB, and additional 100,000 cases of RFP-resistant TB. Of the estimated 580,000 patients that are newly eligible for MDR-TB treatment, only 125,000 (20%) were enrolled in treatment programs. Globally, the MDR-TB treatment success rate was 52% in 2013 [1]. In South Korea, 2.7% of new patients with TB and 14% of patients undergoing retreatment of TB were infected with MDR-TB [2], which continues the decrease in incidence since 2012 [3]. For drug-susceptible TB, the standard therapeutic approach includes a combination of four drugs administered for 6-9 months [4]. In patients with MDR-TB, at least five effective anti-TB drugs during intensive phase are recommended, comprising pyrazinamide and four core second-line anti-TB drugs [5]. The suggested timeline of treatment includes the intensive phase for eight months, based on the use of a parenteral agent, a minimum of an additional four months after culture conversion, and a minimum total length of treatment of 18 months after culture conversion. The duration of treatment may be modified according to the patient’s response to therapy [6]. Overall, treatment of MDR-TB is more expensive, longer, and more toxic as compared to the relatively short-course treatment for drug-susceptible TB. In pulmonary TB, conversion of serial sputum culture results from positive to negative is an important indicator of treatment response and infectious state. Culture or smear conversion after 2 months of treatment is widely used as an indicator of treatment effectiveness in drug-susceptible TB.