Buffering the stomach content enhances the absorption of diflunisal in man

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Abstract
Diflunisal, a lipophilic salicylate, is absorbed more slowly in healthy volunteers than aspirin. In this paper we report on attempts to influence diflunisal absorption by buffering the gastric milieu. Sodium bicarbonate given together and 30 min after diflunisal tablets significantly (p < 0·05) shortened the time to reach peak plasma concentration (tmax > 15 per cent), raised maximum plasma concentration slightly (Cmax 6 per cent) and increased the area under the plasma concentration‐time curve (AUC > 8 per cent). Other pharmacokinetic parameters, including terminal half‐life and renal elimination of the compound, were not considerably influenced. These findings indicate that the absorption of diflunisal was enhanced by increased gastric pH, presumably a result of an increased solubility of diflunisal in the stomach together with faster transport into the small intestine. In one volunteer, after intravenous administration diflunisal plasma concentrations declined in a triphasic manner with a terminal half‐life of 12·8 h. The volume of distribution was approximately 10 per cent of body weight. Based on the ratio of AUC after equivalent i.v. and oral diflunisal doses, the absolute bioavailability was 89·5 per cent.