Comparative study of the influence of Ca2+ on absorption parameters of ciprofloxacin and ofloxacin

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Abstract
A comparative study was undertaken to investigate the influence of calcium on the absorption of ofloxacin and ciprofloxacin. The presence of CaCO3 did not significantly lower the partition coefficients of either fluoroquinolone although values for ofloxacin were significantly higher than those for ciprofloxacin (P = 0.0085). In intestinal sacs, the presence of 5000 mg/L CaCO3 significantly reduced both the absorption constant and the fraction of absorbed dose of 2000 mg/L ciprofloxacin but not 2000 mg/L ofloxacin. When the same concentration of CaCO3 was introduced into the isolated intestinal segments of rats, the absorption of both 200 mg/L ofloxacin and 400 mg/L ciprofloxacin was reduced significantly from 49% and 35% respectively to approximately 30% in each case. Co-administration of 500 mg/L CaCO3 to healthy volunteers significantly reduced the urinary excretion of 250 mg/L ciprofloxacin but not 200 mg/L ofloxacin although neither the fraction of absorbed dose nor the half-lives were markedly affected. Calcium therefore shares the same propensity as other cations in impairing the absorption of ciprofloxacin but not ofloxacin.

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