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Kim MK, Nightingale C, Nicolau D. 
“Influence of sex on the pharmacokinetic interaction of fleroxacin and ciprofloxacin with caffeine”. 
Clin Pharmacokinet. 2003;42(11):985-96.

BACKGROUND: Previous pharmacokinetic studies have shown that a number of the quinolones inhibit the metabolism of caffeine.
OBJECTIVE: To evaluate the effect of sex on the interaction between two quinolones and caffeine.

DESIGN: Multiple-dose, double-blind, randomised, three-period crossover study.

PARTICIPANTS:Twelve male and twelve female healthy volunteers.

METHODS: Subjects received by mouth either fleroxacin 400 mg once daily and caffeine 100 mg three times daily, ciprofloxacin 500 mg twice daily and caffeine 100 mg three times daily, or caffeine alone, for 3 days. Subjects received each of the other regimens after 12-day washout periods. Plasma and urine concentrations were determined by validated high-performance liquid chromatography procedures and the data were analysed by noncompartmental linear pharmacokinetic methods.

RESULTS: Analysis of the interaction by sex revealed that females showed a significant difference in caffeine pharmacokinetics in the presence of ciprofloxacin (area under the concentration-time curve [AUC], peak plasma concentration [C(max)], time to C(max) [t(max)] and apparent total body clearance [CL/F]) and fleroxacin (AUC and CL/F) when compared with males. Significant differences between sexes were also observed in the pharmacokinetics of ciprofloxacin (AUC, elimination rate constant [beta] and CL/F) and fleroxacin (C(max) and beta) in the presence of caffeine. However, these significant differences disappeared when AUC and C(max) were normalised to 70 kg bodyweight and CL/F was expressed as per kg bodyweight. CONCLUSION: The effect of quinolones on the pharmacokinetics of caffeine, and the reciprocal effect, are different between the sexes, due in part to different bodyweights.
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