Clinical meaning
Drug-resistant TB emerges through selection pressure from inadequate treatment regimens, poor adherence, or transmission of resistant strains. MDR-TB is resistant to at least isoniazid and rifampin. XDR-TB (extensively drug-resistant) is MDR-TB plus resistance to a fluoroquinolone and at least one injectable agent. Treatment requires prolonged courses (9-20+ months) with more toxic second-line drugs. The BPaL regimen (bedaquiline, pretomanid, linezolid) represents a breakthrough for treatment-resistant cases.
Diagnosis & workup
Diagnostics & workup: - Order rapid molecular testing: GeneXpert MTB/RIF for rifampin resistance detection (results in 2 hours) - Order full drug susceptibility testing (DST) on all positive cultures - Order liquid culture (BACTEC MGIT) for faster results vs solid media - Order line probe assays for rapid detection of INH and rifampin resistance - Whole genome sequencing for comprehensive resistance profiling - Order baseline audiometry, visual acuity, hepatic panel, renal function, CBC - Monitor therapeutic drug levels for second-line agents