Proton-pump inhibitors (PPIs), frequently prescribed to lower gastric acid secretion, often exert an effect on the absorption of co-medicated drug products. A previous study showed decreased plasma levels of the lipophilic drug ritonavir after co-administration with the PPI Nexium (40 mg esomeprazole), even though duodenal concentrations were not affected. The present study explored if a PPI-induced decrease in gastrointestinal (GI) fluid volume might contribute to the reduced absorption of ritonavir. In an exploratory cross-over study, five volunteers were given a Norvir tablet (100 mg ritonavir) orally, once without PPI pre-treatment and once after a three-day pre-treatment with the PPI esomeprazole. Blood samples were collected for eight hours to assess ritonavir absorption and magnetic resonance imaging (MRI) was used to determine the gastric and duodenal fluid volumes during the first three hours after administration of the tablet. The results confirmed that PPI intake reduced ritonavir plasma concentrations by 40%. The gastric residual volume and gastric fluid volume decreased by 41% and 44% respectively, while the duodenal fluid volume was reduced by 33%. These data suggest that the PPI esomeprazole lowers the available fluid volume for dissolution, which may limit the amount of ritonavir that can be absorbed. Although additional factors may play a role, the effect of PPI intake on the GI fluid volume should be considered when simulating the absorption of poorly soluble drugs like ritonavir in real-life conditions.

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This article describes the development and validation of a liquid chromatographic method for spiramycin using a column with superficially porous particles. Gradient elution was applied and the mobile phase consisted of phosphate buffer (0.2M; pH 8.3) - HO - acetonitrile in a ratio 10:60:30 (v/v/v) for mobile phase A and 10:30:60 (v/v/v) for mobile phase B. UV detection was performed at 232nm. Compared to previous methods, the analysis time was about two times faster and impurities were better separated. Furthermore, impurities which were present above 0.25% were characterized using liquid chromatography coupled with mass spectrometry (LC/MS).