Distribution and antimicrobial activity of ciprofloxacin in human soft tissues

Interstitial ciprofloxacin concentrations in soft tissues were measured by microdialysis following intravenous administration of 200 mg to each of eig ht healthy volunteers. Interstitial ciprofloxacin concentrations were signi ficantly lower than corresponding total serum drug concentrations; the inte rstitium-to-serum concentration ratios ranged from 0.55 to 0.73. An in vitr o simulation based on interstitial pharmacokinetics showed a substantially lower antimicrobial activity than did the simulation based on serum pharmac okinetics. Thus, ciprofloxacin concentrations at the site of effect may be subinhibitory although effective concentrations are attained in serum.