Tradition might reign supreme in some cases, but when it comes to equine pain control researchers are seeking different—and sometimes safer—drugs to use in a variety of circumstances.
Veterinarians often prescribe traditionally used non-steroidal anti-inflammatory drugs (NSAIDs)—such as phenylbutazone (PBZ, Bute), flunixin meglumine (FM, Banamine), and ketoprofen (Ketofen)—for analgesia. But such drugs carry potentially dangerous side effects, including toxicity, ulcer development, decreased plasma protein levels, and renal (kidney) disease.
University of Illinois veterinarians recently tested an alternative to traditional NSAIDs—meperidine, marketed as Demerol—for its ability to treat foot pain in horses. During a presentation at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7011 in Nashville, Tenn., Jonathan H. Foreman, DVM, MS, Dipl. ACVIM, said that while the opioid drug appears effective at treating foot pain, it might have some drawbacks, as well.
To test the drug's efficacy, Foreman and colleagues induced reversible lameness in eight healthy Thoroughbreds by using an adjustable heart bar shoe that could be tightened with a screw to elicit lameness ranging from mild to severe. Then, they randomly assigned each horse to receive either 1 mg/kg of body weight intramuscular (IM) meperidine or saline (to serve as controls) one hour after lameness induction. They monitored the horses' heart rates and lameness scores every 20 minutes for five hours, then hourly for eight hours. The team also collected blood samples from the horses before treatments, five minutes after treatment, and one, two, four, six, eight, 10, and 12 hours after treatment.
The researchers found that:
- Meperidine lowered the horses' heart rates significantly, but only for a brief time period (two to four hours); the treated horses' heart rates eventually rose higher than the controls in the experiment's later hours, Foreman said.
- The drug also reduced treated horses' lameness scores, but, again, only for the same brief period.
- Meperidine's plasma concentration peaked—meaning the drug's highest plasma concentration was identified—at one hour post-administration. "It turns out meperidine peaks very quickly after intramuscular injection," Foreman said.
- Three of the eight horses' meperidine concentrations were below the lower limit of detection (or the lowest quantity of a substance that can be distinguished from an absence of that substance) when measured at 12 hours post-treatment.
In previous research using a similar study design, Foreman has shown that PBZ and FM provide foot pain analgesia for eight to 12 hours. To that end, he concluded that while meperidine provided foot pain relief, "compared to the duration of effect with PBZ and FM, it's significantly shorter."
Because it doesn't put the horse at risk for the negative side effects associated with NSAIDs, "meperidine may provide a suitable non-steroidal alternative, but it would need to be administered more frequently," he said.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.