In vitro susceptibility testing and totally drug-resistant tuberculosis

It is important to consider totally drug-resistant (TDR) tuberculosis (TB) cases as being curable. No case is incurable by definition; we need to re-enforce the message that, although difficult-to-treat, XDRTB cases can have concrete chances of winning their battle against the disease. This message is even more convincing now that we have much improved diagnostic tools e.g. GenXpert and new drugs, e.g. delamanid, bedaquiline and PA-824.
The present evidence on the extent of drug susceptibility testing, as of today, still provides suboptimal predictions for the in vivo effect of second-line anti-TB drugs and further research is needed. In addition, the real impact of the cocktail of anti-TB drugs prescribed on an individual basis is not fully clear. It is difficult, in fact, to attribute cause and effect to each specific drug and the design of prospective clinical trials is also difficult when dealing with XDR-TB and other complicated multidrug-resistant cases.
The therapeutic drug monitoring represents the future for improving the quality of second-line anti-TB drugs prescription. Any contribution in this direction will represent a significant step forward in improving patient management, optimising doses, minimising adverse events and, consequently, maximising the drugs’ effect.