Antibacterial Properties of Gemifloxacin and Trovafloxacin in Urine Ex Vivo: Phase I Study

Abstract

Urine bactericidal titers (UBTs) against Escherichia coli ATCC 25922 and Staphylococcus saprophyticus ATCC 1970 were determined after the administration of single oral doses of gemifloxacin at 320 mg and trovafloxacin at 200 mg to healthy volunteers. Gemifloxacin presented significantly lower experimental versus mathematically predicted UBTs over 72 h, due to the effect of urine on the susceptibility of the E. coli strain. Experimental UBTs were significantly higher for gemifloxacin than trovafloxacin against both strains over 72 h."Ex vivo" activity in urine is important since the measurement of urine antibacterial activity correlates directly with the outcome of infection (4) more than the determination of MICs and the levels of antimicrobials in urine (2), probably because MICs are higher when tested in human urine than in conventional media (6).Urine bactericidal titers (UBTs) and the area under the urine bactericidal curve (AUBC) of gemifloxacin versus trovafloxacin were evaluated against Escherichia coli and Staphylococcus saprophyticus strains.Twelve healthy male volunteers (mean age, 26.2 Ϯ 3.5 years; height, 175.2 Ϯ 4.7 cm; weight, 73.2 Ϯ 4.2 kg) received single oral doses of 320 mg of gemifloxacin (SmithKline Beecham Pharmaceuticals, Harlow, United Kingdom) and 200 mg of trovafloxacin (Trovan; Pfizer Inc., New York, N.Y.), separated by a 14-day washout period. The protocol was approved by the Research Ethics Committee of Hospital La Paz, Madrid, Spain. Written informed consent was obtained from all subjects.Urine samples were collected prior to drug administration (0 h) and at intervals of 0 to 2, 2 to 4, 4 to 8, 8 to 12, 12 to 16, 16 to 24, 24 to 36, 36 to 48, 48 to 60, and 60 to 72 h after dosing for determination of urine concentrations of gemifloxacin and trovafloxacin by high-pressure liquid chromatography (HPLC) and bioassay and for determination of urine bactericidal titers (UBTs).In vitro susceptibility testing was performed using Laboratory reference standards of gemifloxacin and trovafloxacin (SmithKline Beecham Pharmaceuticals, Tonbridge, United Kingdom), five times each for E. coli ATCC 25922 and Staphylococcus saprophyticus ATCC 1970 by standardized methods (5). In addition, the same methodology was followed but using a pool of the volunteer's urine as test media to study the effect of urine on the antibacterial activity of the study drugs.Gemifloxacin and trovafloxacin concentrations were determined by bioassay in plates with nutrient agar (BBL; Becton Dickinson, Cockeysville, Md.) seeded with Bacillus subtilis NCTC 6633 spore suspension (Difco Laboratories, Detroit, Mich.). A total of 90 l of each sample was deposited into 7-mm-diameter wells in the inoculated plates and incubated at 30°C for 18 h. Gemifloxacin and trovafloxacin standards of from 32 to 0.125 g/ml were prepared in pooled urine obtained from volunteers before administration of the drugs. The lower limit of detection was 0.125 g/ml.For HPLC determination, frozen samples were thawed at ambient temperature, agitated at 37°C u...

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