How painkillers can affect colic surgery complications

Reducing the risk of a life-threatening complication of small intestine strangulation colic can be as simple as selecting the right type of analgesic medication.
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Reducing the risk of a life-threatening complication of small intestine strangulation colic can be as simple as selecting the right type of painkiller, according to new research from the University of North Carolina.

The study focused on the role of post-surgical medications on the development of endotoxemia.

“Endotoxemia occurs when the bacterial toxin, called endotoxin, gets across the lining of the gut and activates a massive immune response, causing shock (poor organ blood flow),” explains Anthony Blikslager, DVM, PhD. “The reason it is more likely to occur in small intestinal strangulating obstruction (SISO) of the gut is that the lining of the gut breaks down rapidly in those cases, allowing endotoxin to get across and into circulation. In simple obstructions, like impactions, this takes much longer. “

Inflammatory enzymes, such as COX-2, contribute to pain and inflammation associated with illness, injury and surgery. Nonsteroidal anti-inflammatory drugs (NSAIDs), block this enzyme and are commonly administered after colic surgery. However, COX-1, which is closely related to COX-2, produces prostaglandins that protect the stomach lining. This means that blocking both COX-1 and COX-2 has many benefits, but can also lead to negative gastrointestinal side effects because of the importance of COX-1. Some NSAIDs, such as flunixin meglumine, inhibit both COX-1 and COX-2, while selective inhibitors, such as firocoxib, target only COX-2 inhibitors and produce fewer side effects.

“In this study, the ultimate question was, ‘Does a nonselective NSAID (flunixin---which blocks COX-1 and COX-2) stop the gut from repairing rapidly as compared to a selective NSAID (firocoxib---which blocks COX-2)?’” says Blikslager.

The research was based on 56 horses who underwent surgery to repair SISO at three university clinics over a two-year period. After surgery, the horses were given either firocoxib or flunixin while researchers monitored their pain levels and bloodwork for production of a molecule called soluble CD14 (sCD14), one of the earliest signs of endotoxemia that is released by immune cells when they detect endotoxin.

The data showed that while there was no difference in pain levels among the groups, horses given flunixin had more than three times the risk of having elevated sCD14 in their blood. “The results suggest flunixin does slow down gut repair, allowing more endotoxin to get across,” says Blikslager. “This makes it less desirable, despite its ability to control signs of pain.”

Based on the findings of this study, Blikslager says he’d recommend giving horses a selective COX-2 inhibitor following SISO surgery, “because it treats pain well, but reduces the risk of slow gut repair and endotoxemia. In fact, for any horse in the field suspected of the beginning stages of SISO, I would use a selective COX-2 inhibitor. The next phase of this study is to take it to the field, because once flunixin is used, it takes up to 24 hours for COX-1 activity to come back.”

Reference:“Multicentre, blinded, randomised clinical trial comparing the use of flunixin meglumine with firocoxib in horses with small intestinal strangulating obstruction,” Equine Veterinary Journal, August 2018

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