This study investigated the margin of safety of the COX-2e inhibitor, meloxicam on blood cells and gastrointestinal tract of dogs. After a clinical and laboratorial examination, the dogs were distributed in the following groups: I (placebo; n=3), II (piroxicam: 1.0mg kg-1; n=5), III (meloxicam: 0.2mg kg-1; n=5), IV (meloxican: 1.0mg kg-1; n=5) and V (meloxican: 2.0mg kg-1; n=5). The drugs were given orally for 16 days. On the 17th day the complete hemogram was repeated and the euthanasia and necropsy were then accomplished. In group I there were no significative alterations. In group II, all the dogs showed moderate episodes of vomit and diarrhea. The blood-cell profile was not modified. Two dogs had hematocrit and hemoglobin reduction. In the necropsy, hemorrhagic spots and moderate gastroduodenal lesions were seen. The microscopic analysis revealed the presence of gastritis and ulcerative enteritis. In group III, four dogs (80%) showed vomit and diarrhea, without alteration in blood-cell profile. The microscopic analysis showed mild lesions in the gastric mucosa and hemorrhagic spots in the duodenum of four dogs. Histology showed lesions suggesting mild gastroenteritis. In group IV, all the dogs (n=5) showed vomit and blood diarrhea. Four of them showed anemia (p <0.05). Four and five dogs, respectively, had hematocrit and hemoglobin reduction. In addition, there was a significant (p<0.05) leukocytosis, neutrophilia and linfopenia in 60% of the dogs. The necropsy showed hiperemia, hemorrhage and severe gastric ulcers in all the dogs. In the microscopic analyses, gastroenteritis ulcerative was present in all the animals. In group V, the dogs (n=5) had serious vomit, diarrhea and melena episodes. The dogs that bore the treatment (n=4) had anemia and leukocytosis with neutrophilia and linfopenia significatives (p<0.05). All the dogs had hematocrit and hemoglobin reduction. In the necropsy, hemorrhages and severe gastroduodenal ulceration were seen. The microscopic analysis showed severe gastroenteritis. It can be concluded that, although meloxicam is a COX-2 selective inhibitor, it induces deleterious effects on gastrointestinal tract and blood cells of dogs, when given five or ten times the therapeutic dose, which demonstrate its low margin of safety in this animal specie.
antiinflammatory; cyclooxygenase-2; toxicity
