Disposition, metabolism, and excretion of [14C]doripenem after a single 500-milligram intravenous infusion in healthy men.

In this open-label, single-center study, eight healthy men each received a single 500-mg dose of [(14)C]doripenem, containing 50 microCi of [(14)C]doripenem, administered as a 1-h intravenous infusion. The concentrations of unchanged doripenem and its primary metabolite (doripenem-M-1) resulting from beta-lactam ring opening were measured in plasma and urine by a validated liquid chromatography method coupled to a tandem mass spectrometry assay. Total radioactivity was measured in blood, plasma, urine, and feces by liquid scintillation counting. Further metabolite profiling was conducted on urine samples using liquid chromatography coupled to radiochemical detection and high-resolution mass spectrometry. Unchanged doripenem and doripenem-M-1 accounted for means of 80.7% and 12.7% of the area under the plasma total-radioactivity-versus-time curve (area under the concentration-time curve extrapolated to infinity) and exhibited elimination half-lives of 1.1 and 2.5 h, respectively. Total clearance of doripenem was 16 liters/h, and renal clearance was 12.5 liters/h. At 7 days after the single dose, 95.3% of total doripenem-related radioactivity was recovered in urine and 0.72% in feces. A total mean of 97.2% of the administered dose was excreted in the urine as unchanged doripenem (78.7% +/- 5.7%) and doripenem-M-1 (18.5% +/- 2.6%). Most of the urinary recovery occurred within 4 h of dosing. Three additional minor metabolites were identified in urine: the glycine and taurine conjugates of doripenem-M-1 and oxidized doripenem-M-1. These results show that doripenem is predominantly eliminated in urine as unchanged drug, with only a fraction metabolized to doripenem-M-1 and other minor metabolites.

Pharmacokinetic considerations and efficacy of levofloxacin in an inhalational anthrax (postexposure) rhesus monkey model.

Because the treatment of inhalational anthrax cannot be studied in human clinical trials, it is necessary to conduct efficacy studies using a rhesus monkey model. However, the half-life of levofloxacin was approximately three times shorter in rhesus monkeys than in humans. Computer simulations to match plasma concentration profile, area under the concentration-time curve (AUC), and time above MIC for a human oral dose of 500 mg levofloxacin once a day identified a dosing regimen in rhesus monkeys that would most closely match human exposure: 15 mg/kg followed by 4 mg/kg administered 12 h later. Approximately 24 h following inhalational exposure to approximately 49 times the 50% lethal doses of Bacillus anthracis (Ames strain), monkeys were treated daily with vehicle, levofloxacin, or ciprofloxacin for 30 days. Ciprofloxacin was administered at 16 mg/kg twice a day. Following the 30-day treatment, monkeys were observed for 70 days. Nine of 10 control monkeys died within 9 days of exposure. No clinical signs were observed in fluoroquinolone-treated monkeys during the 30 treatment days. One monkey died 8 days after levofloxacin treatment, and two monkeys from the ciprofloxacin group died 27 and 36 days posttreatment, respectively. These deaths were probably related to the germination of residual spores. B. anthracis was positively cultured from several tissues from the three fluoroquinolone-treated monkeys that died. MICs of levofloxacin and ciprofloxacin from these cultures were comparable to those from the inoculating strain. These data demonstrate that a humanized dosing regimen of levofloxacin was effective in preventing morbidity and mortality from inhalational anthrax in rhesus monkeys and did not select for resistance.