TB Control and Access to Second-Line Drugs: Better Model Needed. (Round Table Discussion)

Abstract

Pablos-Mendez et al. rightly point out that multidrug-resistant tuberculosis (MDR-TB) is hot a major pandemic (see pp. 489-494). However, as drug-susceptible TB is a worldwide problem, the first priority for national TB programmes should be the implementation or expansion of the DOTS strategy. MDR-TB is in most cases a sign of poor programme performance, although there may be highly virulent strains spreading rapidly. A weak national programme can do more harm than good if its main focus is the widespread introduction of second-line drugs to manage this problem. To tackle MDR-TB Pablos-Mendez et al. propose a matrix based on two variables: treatment success for new TB cases, and prevalence of primary MDR-TB. They propose that the use of second-line drugs should be limited to countries which belong in specified quadrants according to these two variables. We find it questionable that the management of a MDR-TB, or any other disease, should be based on only two variables. We lire in a world in which the control of illness calls for modern multidisciplinary approaches (1). We will come back to this point. The proposal of Pablos-Mendez et al. is difficult to accept for at least two reasons. Firstly, more than two variables axe needed to decide if a country should treat MDR-TB. For instance, a country may score well on treatment success, have a low number of primary MDR-TB cases but still have a high number of treatment failure cases (a variable hot taken into account in the proposed model), which axe likely to have MDR (2). Such a country may need to implement management of MDR-TB as well as DOTS, regardless of its level of primary MDR and treatment success, Furthermore, treatment success could be a very misleading variable since it is the result of cure plus treatment completion. There axe some examples of poor national TB programmes having high rates of success upon completion of treatment but low cure rates. Secondly, do we really need cut-off points to manage a disease? On what basis can we choose 5% and not, say 3% for MDR prevalence, or 70% and not, say, 60% for treatment success? No biological, statistical or epidemiological reason is given for choosing such cut-off points. A straightforward indication of the point at which to start management of MDR-TB could be helpful, but the issue is hot that simple, and other matters need to be carefully looked at when taking such a decision. The assertion that DOTS can reduce MDR-TB has not been fully proved, although it is clear that short-course chemotherapy can prevent MDR-TB. Countries that have reduced MDR-TB have also used second-line drugs and it is not clear to what extent the use of both first-line and second-line drugs have contributed to reducing MDR-TB. …