Analgesic Efficacy of Non-Steroidal Anti-Inflammatory Drug Therapy in Horses with Abdominal Pain: A Systematic Review

SIMPLE SUMMARY: The use of non-steroidal anti-inflammatory drugs, that primarily act via the inhibition of COX isomers, is one of the most common therapeutic means to control abdominal pain in horses. However, these drugs can elicit gastrointestinal side effects. Drugs that are more selective for COX-2 inhibition are considered to cause less adverse effects. Despite some physiological effects of the COX-2 isoform, it is mainly induced by inflammatory processes, whereas the COX-1 isoform has a protective role and is considered to be constitutive. Despite the availability of several non-steroidal anti-inflammatory drugs with varying degrees of COX isoform inhibition, non-selective molecules remain the most frequently prescribed non-steroidal anti-inflammatory drugs. This is likely because the analgesic effect achieved by COX-2-selective drugs is not considered sufficient. To date, the scientific evidence concerning the analgesic efficacy of non-steroidal anti-inflammatory drugs in the treatment of abdominal pain in horses still remains uncertain. This systematic review showed that the current scientific literature cannot adequately justify the therapeutic choice of one non-steroidal anti-inflammatory drug over another for the treatment of abdominal pain in horses. Therefore, prospective randomised blinded clinical trials are deemed necessary to elucidate the analgesic efficacy of non-steroidal anti-inflammatory drugs in the treatment of abdominal pain in horses. ABSTRACT: This systematic review aimed to identify the evidence concerning the analgesic efficacy of non-steroidal anti-inflammatory drugs to treat abdominal pain in horses, and to establish whether one non-steroidal anti-inflammatory drug could provide better analgesia compared to others. This systematic review was conducted following the “Systematic Review Protocol for Animal Intervention Studies”. Research published between 1985 and the end of May 2023 was searched, using three databases, namely, PubMed, Embase, and Scopus, using the words equine OR horse AND colic OR abdominal pain AND non-steroidal anti-inflammatory drug AND meloxicam OR flunixin meglumine OR phenylbutazone OR firocoxib OR ketoprofen. Risk of bias was assessed with the SYRCLE risk of bias tool, and level of evidence scored according to the Oxford Centre for Evidence-based Medicine. A total of 10 studies met the inclusion criteria. From those only one study judged pain with a validated pain score, and a high risk of bias was identified due to the presence of selection, performance, and “other” types of bias. Therefore, caution is required in the interpretation of results from individual studies. To date, the evidence on analgesic efficacy to determine whether one drug is more potent than another regarding the treatment of abdominal pain in horses is sparse.