The purpose of this study is to evaluate the effectiveness and safety of two antibiotics in the treatment of complicated urinary tract infection or acute pyelonephritis (kidney infection). A 5-day course of 750 milligrams of levofloxacin given intravenously and/or by mouth once daily will be compared to a 10-day course of 400 milligrams of ciprofloxacin given intravenously and/or 500 milligrams of ciprofloxacin given by mouth twice daily.

Levofloxacin has been approved in both its oral and intravenous forms to treat a large number of infections caused by bacteria. Levofloxacin and other members of a class of antibiotics known as fluoroquinolones have been used successfully to treat urinary and kidney infections. This study will compare the effectiveness and safety of levofloxacin given for 5 days to that of another fluoroquinolone, ciprofloxacin, given for 10 days in treating complicated urinary tract infection or acute pyelonephritis (kidney infection). A shorter course of antibiotics may help patients take all of their medication, which is critically important for curing the infection. A shorter course may also help prevent the development of bacteria that cannot be killed by antibiotics. Patients will take 750 milligrams of levofloxacin intravenously and/or by mouth once daily for 5 days or 400 milligrams of ciprofloxacin intravenously and/or 500 milligrams of ciprofloxacin by mouth twice daily for 10 days. To prevent the study doctor, study staff and patients from knowing which study drug they are taking, all study drug will manufactured to look the same and patients on the 5-day regimen will be given placebo for the last 5 days of their participation in the study. The intravenous infusion bags will be covered so that the solution cannot be seen. The objective of the study is to demonstrate that 5 days of levofloxacin once daily is at least as effective as 10 days of ciprofloxacin twice daily in treating complicated urinary tract infection or acute pyelonephritis. Patients will take 750 milligrams of levofloxacin intravenously and/or by mouth once daily for 5 days or 400 milligrams of ciprofloxacin intravenously and/or 500 milligrams of ciprofloxacin by mouth twice daily for 10 days.

Inclusion Criteria:

• Positive dipstick test for leukocyte esterase AND/OR at least 5 white blood cells per centrifuged urine sediment AND/OR at least 10 white blood cells per microliter of uncentrifuged urine
• outpatient or inpatient (in hospital, nursing home, or other extended-care facility)
• clinical diagnosis of either complicated urinary tract infection or acute pyelonephritis.

Exclusion Criteria:

• Allergy or serious adverse reaction to levofloxacin, ciprofloxacin, or other fluoroquinolone
• urinary tract surgery or lithotripsy (treatment for kidney stones) within 7 days before study entry
• a second coexisting bacterial infection that requires systemic antibiotics
• need for a second antibiotic to treat the urinary tract infection
• obstruction of the urinary tract
• prostate infection.