The effect of ferrous sulphate on the absorption of norfloxacin, ciprofloxacin and ofloxacin.

The effect of ferrous sulphate on the absorption of norfloxacin, ciprofloxacin and ofloxacin was studied in three separate, two-period crossover trials, each involving eight healthy volunteers. After an overnight fast, a single dose of norfloxacin (400 mg), ciprofloxacin (500 mg) or ofloxacin (400 mg) was administered with and without ferrous sulphate (corresponding to 100 mg elemental iron). The absorption of all the fluoroquinolones studied was significantly reduced when they were co-administered with ferrous sulphate. The reduction in the area under the plasma drug concentration-time curve from 0 to 24 h was most marked in the case of norfloxacin, while ofloxacin was least affected by ferrous sulphate. The AUC of norfloxacin was reduced by 73% (P < 0.001) and its peak plasma concentration by 75% (P < 0.01) by concomitant ingestion of ferrous sulphate. The AUC and peak plasma concentration of ciprofloxacin were reduced by 57% (P < 0.001) and 54% (P < 0.01), respectively, by ferrous sulphate. Concomitant ingestion of ferrous sulphate reduced the AUC and peak plasma concentration of ofloxacin by 25% (P < 0.01) and 36% (P < 0.01), respectively. Similar results were obtained with respect to the urinary recoveries of each fluoroquinolone. We recommend that norfloxacin and ciprofloxacin should not be taken together with ferrous sulphate. It would also be advisable not to take ofloxacin with ferrous sulphate, especially if the organism causing infection is only moderately susceptible.