Morphine Controls Pain Within Joints, Researchers Report

Researchers from Denmark and Norway report that morphine within a joint appears to be a useful part of a multimodal pain management protocol for horses that have undergone arthroscopic surgery.

Morphine is widely employed in human medicine after arthroscopic procedures; however, there is a reluctance to use the drug in equine medicine because unwanted side effects such as excitation, sedation, and reduced gastrointestinal motility.

Thus, alternative routes of administration using reduced doses of the drug could potentially decrease the side effects but still help control pain.

According to the study authors, "The discovery of opioid receptors in the equine synovial membrane makes it plausible that (intra-articularly) administered morphine may have analgesic and anti-inflammatory properties in horses."

To investigate the analgesic effect of intra-articular (IA) compared to intravenous (IV) morphine, Casper Lindegaard, DVM, PhD, from the Department of Large Animal Sciences at the University of Copenhagen, and colleagues, induced acute synovitis in eight healthy adult horses. Horses were administered morphine either IA or IV. Two observers subsequently assessed lameness and pain over the 168-hour study period.

Key findings were:

  • IA morphine resulted in significantly less lameness than IV morphine;
  • Pain was not significantly different between the two groups as determined via two separate pain scales (visual analog scale and the composite measure pain scale).

Based on these results, the research team noted, "A definite analgesic effect of IA morphine (0.05 mg/kg) was demonstrated by significantly lower lameness scores after IA compared to IV morphine in horses with LPS-induced joint pain."

This supports the common practice of including IA morphine in the post-arthroscopic analgesic protocol. The study authors did add, however, that further studies in clinical classes are needed.

The study, "Analgesic efficacy of intra-articular morphine in experimentally induced radiocarpal synovitis in horses," was published in the March 2010 edition of the journal Veterinary Anesthesia and Analgesia. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.