**12. Totally drug-resistant tuberculosis**

Totally drug-resistant tuberculosis (TDR-TB or XXDR-TB) was recently defined as TB bacilli which resist to all first-line and the 6 second-line drugs (para-aminosalicylic acid, fluoroqui‐ nolones, aminoglycosides, thiamines, polypeptides, and cycloserine) [75]. Meanwhile, a recent report from the US-CDC listed 7 challenges that should be addressed before new terminology of TDR-TB should be considered for adopting [76], following are the challenges:


with DST of several anti-TB agents, the lack of standardized DST methods for several present and new investigational drugs, and insufficient evidence to link such DST results to patients' treatment outcomes [78]. No DST methods for group 5 and new investigational agents currently exist [78]. Molecular DST for the second-line drugs cannot yet replace phenotypic methods [78]. Collaboration between the national TB control programme, Ministries of Public Health, and the pharmaceutical companies will be required to resolve the limitations of treatment options by the compassionate use of new anti-TB agents [78]. The WHO will be the lead in ensuring that better patient data provide a more robust information for future policy decision [78].
