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Adaptation of rat gastric mucosa to repeated doses of non‐salicylate non‐steroidal anti‐inflammatory drugs

To determine whether gastric mucosal adaptation occurs to the damaging effects of repeated non‐steroidal anti‐inflammatory drug (NSAID) administration, we compared the extent of gastric damage in rats after single or repeated doses of four non‐salicylate NSAID. With daily dosing, adaptation occurred only to repeated doses of the short‐acting NSAID ibuprofen and diclofenac but not to indomethacin and naproxen, both of which have considerably longer half‐lives. Adaptation to indomethacin was demonstrable if the dosage interval was lengthened and the drug was given on alternate days rather than daily. Histological examination of the gastric mucosa of diclofenac‐treated rats showed a similar degree of superficial damage in the single and repeatedly dosed groups. However there was a highly significant reduction in the amount of deeper mucosal damage in the repeatedly dosed rats. Our findings show that under certain conditions of dosage, adaptation to non‐salicylate NSAID is demonstrable. The pharmacokinetics of individual NSAID appear to be important in determining whether or not adaptation occurs. Histological examination showed that adaptation to one of the shorter acting NSAID, diclofenac, was characterized by a significant reduction in deeper mucosal damage.