Carprofen interferes with early repair of ileal anastomoses in the rat. Signs of anastomotic leakage comprise the main outcome parameter in this study. If carprofen is used from the day of operation, these signs are already abundantly present 24 hours later. Delaying the first gift of carprofen for 48 hours significantly reduces signs of leakage, without completely preventing them. Reducing the dose fourfold lowers the incidence of this complication, but not significantly so.
NSAIDs are commonly used in small animals and equine practice for peri-operative pain relief because of their analgetic and anti-inflammatory features. NSAIDs inhibit the family of COX enzymes. COX-2 is expressed mainly in response to external stimuli and is postulated to be involved in essentially pathological conditions such as inflammation, pain and fever . Selective inhibitors of COX-2 supposedly allow specific targeting of inflammatory disease processes, without disruption of normal homeostatic mechanisms that accounts for many side-effects of non-selective NSAID therapy. Both COX-1 and −2 are believed to be involved in wound healing [10, 11] and Figure 1 demonstrates their presence in the healing anastomosis. There is a growing understanding that NSAIDs, and especially those with a certain preference for COX-2, may increase the risk of anastomotic leakage [12, 13]. Carprofen is such a drug that is used in domestic animals , but is also effective as an analgesic in laboratory animals undergoing laparotomy . Recent evidence shows that its long-term use can inhibit bone healing in dogs , but nothing is known about its potential effects on soft tissue healing. Recent incidental reports suggest that carprofen administration to dogs alters functions of platelets, which are relevant to the repair sequence . Also, carprofen has been shown to compromise the integrity and barrier function of the gastrointestinal mucosa in dogs . The present data, which expand on a previous short communication  unequivocally demonstrate that carprofen can interfere significantly with anastomotic integrity in the rat small bowel.
While signs of leakage in the carprofen group greatly surpass those in the buprenorphine group (Table 1), the average anastomotic strength is not dramatically reduced (Figure 1). It seems likely that in the majority of animals the leakage can be contained, e.g. by the formation of fibrinous adhesions. This way, some degree of strength is restored to the anastomotic segment. On the whole though, throughout the three experiments anastomoses which display signs of leakage at necropsy display lower bursting pressures than those that are free of such signs. These findings raise the question what the fate would have been of the animals which survive until day 3 or later, but which show signs of leakage. Most likely, those with zero bursting pressure, thus in fact with a gap in the suture line at that time, will eventually die from secondary peritonitis. However, the possibility cannot be excluded that in some cases a fibrinous adhesion barrier will prevent full feacal leakage into the abdominal cavity. The resulting subclinical leakage could eventually allow complete healing of the intestinal wall. just as the majority of animals with anastomotic strength compatible with normal repair at day 3 may be expected to survive and show increasing strength in the proliferative phase of healing (as observed in the animals in experiment 2).
From the data presented it is clear that, whatever mechanism is responsible for leakage to occur, the origin of the phenomenon must lie within the first days after operation. It is not confined to the first 24, or even 48, hours since in the group where carprofen was first given at day 2, 20% of the animals still showed proof of leakage 3 days later (Table 2). Thus, carprofen somehow affects the inflammatory phase of healing, where anastomotic integrity is determined by the capacity of the existing submucosal matrix to retain sutures. Induction of massive matrix degradation seems unlikely since hydroxyproline (collagen) levels in the anastomotic segments remain unaffected. Also, total activities of MMP-2 and MMP-9 remain unchanged during the first 2 days. These results do not exclude the possibility of limited and local matrix degradation, e.g. around the sutures, by one of the other enzymes from the MMP family. Still, it is believed that COX-2 inhibitors generally suppress MMP activity .
It has been suggested that COX-2 plays a regulatory role in maintaining gastrointestinal barrier function and motility and is needed to maintain small bowel integrity [20, 21].
Interestingly, the effect described here does not occur in colonic anastomoses  while the highest level of COX-2 expression in normal uninjured rats is located on the ileal side of the ileocaecal junction . The question then arises if the carprofen effect is mediated specifically through COX-2 and if it is species specific. It has been suggested that determining the exact specificity of any inhibitor for either of the COX enzymes is frought with practical difficulties and may depend on the test and the laboratory that uses it . Still, carprofen seems to possess a certain degree of specificity for COX-2, although it may vary between species. Thus, as yet the question remains if these findings are limited to laboratory animals or that they can also occur in dogs and cats. Using a commercially available formulation and the manufacturer’s recommended dose it seems likely that carprofen also produces significant inhibition of COX-1 . Very recent data from our own laboratory suggest that diclofenac, another inhibitor with specificity for COX-2, shows effects similar to carprofen, while naproxen, with a suspected lesser specificity for COX-2, leaves ileal anastomoses intact (unpublished results), Older data indicate increased complications in rats with anastomoses in both ileum and colon after preoperative administration of either ibuprofen or indomethacin . It thus remains to be determined if preference for COX-2 is essential for a drug to exert the negative effects observed.
It is necessary to gain knowledge about the potential drawbacks of NSAID’s like carprofen, as they are rapidly becoming cornerstones in peri-operative pain relief and are able to minimize post-operative opioid requirement in veterinary practice and in experimental studies [2–24]. The findings reported here may also be relevant to the human situation where NSAIDs are frequently used after gastro-intestinal surgery and are even incorporated in protocols for fast track surgery, despite emerging evidence that they may affect repair [12, 13].
Thus, we conclude that carprofen interferes with wound healing in the rat ileum at a very early stage. If it does not kill the animal, at least it renders it more vulnerable to second hits after initial surgery. Although the mechanisms responsible remain to be fully understood, there appears to be an increasing body of evidence which suggests that one should be aware that NSAIDs may affect the outcome of the wound healing sequence.