Levofloxacin is a second-generation fluoroquinolone and is the levo isomer of the racemate ofloxacin. Ofloxacin and levofloxaxin were synthesized and developed by scientists at Daiichi Seiyaku.Daiichi, working with Johnson & Johnson, obtained FDA approval in 1996 under the brand name Levaquin to treat bacterial sinusitus, bacterial exacerbations of bronchitis, community-acquired pneumonia, uncomplicated skin infections, complicated urinary tract infections, and acute pyelonephritis. Levofloxacin is on the World Health Organization's List of Essential Medicines. Along with other antibiotics it may be used to treat tuberculosis, meningitis, or pelvic inflammatory disease. It is available by mouth, intravenously, and in eye drop form. TBTC 32/NIAID OPTI-Q Phase 2 study will determine the levofloxacin dose and exposure that achieves the greatest reduction in M. tuberculosis burden with acceptable tolerability by studying 100 adults with smear- and culture-positive pulmonary MDR-TB at sites in Peru and South Africa. Levofloxacin (11, 14, 17, 20 mg/kg) will be administered with an optimized background regimen (OBR) to: Determine the levofloxacin AUC/MIC that provides the shortest time to sputum culture conversion in solid medium. Determine the highest levofloxacin AUC that is both safe and associated with fewer than 25% of patients discontinuing or reducing their dose of levofloxacin. Develop a dosing algorithm to achieve the levofloxacin AUC associated with maximal efficacy and acceptable safety/tolerability.