sentences:  Treatment of MDR-TB requires second-line drugs (i.e., fluoroquinolones, aminoglycosides, and others), which in general are less effective, more toxic and much more expensive than first-line drugs.Treatment schedules for MDR-TB involving fluoroquinolones and aminoglycosides can run for 2 years, compared to the 6 months of first-line drug treatment, and cost over US$100,000.If these second-line drugs are prescribed or taken incorrectly, further resistance can develop leading to XDR-TB.