The influence of chronic administration of calcium carbonate on the bioavailability of oral ciprofloxacin.

Six healthy male volunteers participated in a two-period, two-treatment study to determine the effect of chronic calcium carbonate administration on ciprofloxacin bioavailability. There was a mean reduction of 40% in Cmax and 43% in AUC when calcium carbonate was administered with ciprofloxacin, compared with ciprofloxacin alone (P < 0.05). There were no changes in either half-life or tmax. It is therefore recommended that patients being treated with ciprofloxacin for serious infections refrain from ingesting calcium supplements. If this is not possible, administration of ciprofloxacin 2 h before ingestion of the supplement is suggested.