Pyrazinamide > Ethambutol > Flouroquinolones. (moxifloxacin preferred) > rifabutin > cycloserine > ethionamide > PAS > clarithromycin > Linezolid > IFN - a > thioridazine. Extensive drug resistance TB ( XDR -- TB) is referred to resistance to rifampicin and isoniazid as well as to quinolone and at least one of the following second line drug kanamycin, capreomycin or amikacin. XDR -- TB = resistance to INH, rifampcin, Quinolone, and capreomycin/kanamycin/ amikacin">