Interaction of salicylates and other non-steroidal anti-inflammatory agents in rats as shown by gastro-ulcerogenic and anti-inflammatory activities, and plasma concentrations.

The interaction of salicylates and other non-steroidal anti-inflammatory drugs was studied in rats. Concurrent oral administration of sodium salicylate (SS) or salicylic acid (SA) and indomethacin (IND) significantly reduced the gastro-ulcerogenicity and the plasma concentrations of IND. Acetylsalicylic acid (ASA) failed to do so. IND had no significant influence on plasma concentrations of SA. Simultaneous administration of SS and IND intraperitoneally or subcutaneously showed the same pattern of interaction as for oral administration. Concurrent oral administration of SS and IND exerted similar anti-inflammatory activity as the single drugs. SS significantly antagonized the ulcerogenicity of ibuprofen and tended to antagonize the ulcerogenic activity of ASA, phenylbutazone, tolfenamic acid and naproxen. The results suggest that in rats SS and SA (but not ASA) interact with IND concerning both gastro-ulcerogenicity and plasma concentrations of IND (but not of SA) and that the interaction is systemic in nature. We propose that the ulcerogenic interaction might be explained partly by the reduced IND plasma concentrations and partly by a weaker inhibition by SS of the prostaglandin system in the rat stomach.