Table 1.

Patterns of Initial and Acquired Resistance to Second-Line Injectable Drugs and Fluoroquinolones Among Patients With Multidrug-Resistant (MDR) Tuberculosis. Initial Resistance Signifies Resistance at Diagnosis of MDR Tuberculosis Before Starting Treatment With a Second-Line Drug Regimen; Acquired Resistance, Signifies Resistance that Develops During (and due to) Treatment With a Second-Line Regimen in The Same Strain as The Initial Pretreatment Strain, Confirmed by Genotyping.

5 Major Categories	All 9 Categories	Explanation
Plain MDR tuberculosis	Plain MDR tuberculosis	Initial resistance to isoniazid and rifampicin without resistance to FQs or SLIs (kanamycin, amikacin, and capreomycin), irrespective of resistance to other drugs
Initial pre-XDR tuberculosis	Initial SLI resistance	Plain MDR tuberculosis with additional initial resistance to an SLI
	Initial FQ resistance	Plain MDR tuberculosis with additional initial resistance to an FQ
Acquired pre-XDR tuberculosis	Acquired SLI resistance	Plain MDR tuberculosis with acquired resistance to an SLI
	Acquired FQ resistance	Plain MDR tuberculosis with acquired resistance to an FQ
Initial XDR tuberculosis	Initial XDR tuberculosis	MDR tuberculosis plus additional resistance to both an SLI and an FQ
Acquired XDR tuberculosis	Acquired SLI and FQ resistance	Plain MDR tuberculosis that acquires resistance to both an SLI and an FQ
	Acquired SLI resistance	Pre-XDR tuberculosis (with initial FQ resistance) that acquires resistance to an SLI
	Acquired FQ resistance	Pre-XDR tuberculosis (with initial SLI resistance) that acquires resistance to an FQ

Abbreviations: FQ, fluoroquinolones; MDR, multidrug-resistant; SLI, second-line injectable drugs; XDR, extensively drug-resistant.