Original Paper Veterinarni Medicina, 58, 2013: (8): 430–436 430 Efect of selected non-steroidal anti-infammatory drugs on the pathomorphology of the mucous membrane of the canine colon M. Szweda 1 , J. Szarek 1 , K. Dublan 1 , M. Gesek 1 , T. Mecik-Kronenberg 2 1 University of Warmia and Mazury, Olsztyn, Poland 2 Medical University of Silesia, Zabrze, Poland ABSTRACT: Non-steroidal anti-inflammatory drugs (NSAIDs) have been commonly used for the management of chronic pain caused by inflammatory joint disease in dogs. Although effective at relieving pain and inflam- mation, NSAIDs are associated with a significant risk of serious gastrointestinal side effects. The present study was therefore designed to investigate the effects of carprofen as a poorly-selective COX (cyclooxygenase) inhibi- tor and robenacoxib as a selective COX-2 inhibitor on the colon mucosa. A biopsy of the gastrointestinal tract was performed before treatment and on the last day of treatment with orally-administered carprofen (Group I), robenacoxib (Group II) and empty gelatine capsule (Group III) for twenty-one days in a randomised study. The most evident microscopic lesions in the colonic mucosa in young beagles were caused by a 21-day treatment with robenacoxib. The infiltration with inflammatory cells in the lamina propria of the colonic mucosa was the most commonly-found histopathological lesion. Keywords: carprofen; robenacoxib; cyclooxygenase; beagle; gastrointestinal tract; inflammatory cells List of abbrevations ARI = absolute risk increase, BM = body mass, CBC = complete blood count, COX = cyclooxygenase, GI = gastro- intestinal, IC 50 = half maximal inhibitory concentration, NSAIDs = non-steriodal anti-inflammatory drugs, PGE 2 = prostaglandin, PGI 2 = prostacyclin Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of chronic pain caused by arthritis in dogs. They have potent analgesic and anti-inflammatory activity, inhibit transmission in the nociceptors and are indicated for prevention and treatment of joint oedema and inflammation, especially in the musculoskeletal system (Lascelles et al. 2005, 2007). NSAIDs are one of the best medicaments to prevent and treat post- surgical pain in dogs (Mathews 2000). A search for novel non-steroidal anti-inflammatory drugs has been simultaneously pursued in two directions: (1) towards finding compounds with more potent anti-inflammatory activity and (2) substances with less-severe adverse effects (Miedzybrodzki 2004; Bjorkamn 2006). All NSAIDs have a similar mecha- nism of activity, which consists in inhibiting the activity of cyclooxigenase – an enzyme which par- ticipates in one of the pathways of arachidonic acid transformation (Sakamoto et al. 2006; Lascelles et al. 2007). Cyclooxygenase has at least three iso- forms. COX-1 has been described as a constitutive isozyme (a so-called “good” isozyme) whose final products may be involved in physiological process- es (protective effects on the gastrointestinal tract, maintenance of correct kidney function, regulation of homeostasis) (Clark et al. 2003; Deneuche et al. 2004), whereas COX-2 has been described as an inducible isozyme (a so-called “bad” isozyme) whose final products take part only in pathologi- cal processes (such as pain, inflammation, fever, inhibition of apoptosis) (Dow et al. 1990; Esteve et al. 2005). COX-3 is a recently-discovered COX iso- form whose role in the inflammatory reaction has