Background: Newer NSAIDs that more selectively target the induced isoform of the cyclooxygenase enzyme (COX2) activity might reduce adverse effects while preserving therapeutic benefits of these drugs.Objectives: To compare the effect of oral administration of multiple dose rates of meloxicam and phenylbutazone (PBZ) on gastric mucosal integrity in horses.Animals: Twenty-five light breed horses. Methods: In vivo toxicity study. Horses were randomly assigned to 5 treatment groups, receiving placebo, PBZ (4.4 mg/kg PO q12h day 1, 2.2 mg/kg PO q12h for 4 days, 2.2 mg/kg PO q24h for 9 days), or 3 dose rates of meloxicam (0.6 mg/kg q24h, 1.8 mg/kg q24h, 3.0 mg/kg q24h) for 14 days. Sucrose permeability testing was performed on Day 0 (before treatment) and on Day 13. All personnel involved with data collection or analysis were blinded to treatment.Results: Administration of PBZ at the above dose rate significantly increased gastric permeability to sucrose, evidenced by increased peak serum sucrose concentrations (280-1,580 pg/lL, P = .001) after treatment. Similar changes were not evident after administration of meloxicam at any dose rate tested, or in control horses (P > .05). Treatment was not associated with significant differences in ulceration of the squamous or glandular mucosa. Peak sucrose concentrations were not correlated with serum total protein or albumin concentrations (R 2 = À0.07, P = .61, R 2 = À0.08, P = .58, respectively). Conclusion and Clinical Importance: These results suggest that PBZ was associated with greater compromise to gastric mucosal integrity than meloxicam.

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