Cerebral blood flow (CBF), glucose (FDG), and oxygen metabolism (OM) were evaluated by positron emission tomography (PET) in 18 healthy volunteers who were randomized to a 72-hour course of either 600 mg/d of fleroxacin or placebo. Such studies attempted to assess potentially serious, yet unexplained, central nervous system adverse effects of the fluorinated quinolone class. Baseline and postplacebo values for CBF (mL/min/100 g) and FDG (mg/min/100 g) were: 53 ± 6 and 5.7 ± 1.8; and 49.6 ± 4.4 and 5.2 ± 1.2, respectively. Identical values for fleroxacin were: 53.9 ± 4.8 and 6.3 ± 1.1; and 54.4 ± 2.2 and 6.8 ± 1.5, respectively. The differences between fleroxacin and placebo were not significant. There was also no effect seen in OM between placebo and the active drug. The authors conclude that short-term administration of fleroxacin does not alter CBF, FDG, or OM in healthy volunteers.