Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, U.K.
Joint pain due to osteoarthritis (OA) is one of the major causes (60%) of lameness and lost training days in horses. To alleviate this pain, veterinarians most often turn to non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids, but how do all the different medications stack up against each other? René van Weeren, DVM, PhD, Dipl. ECVS, from the University of Utrecht's Faculty of Veterinary Medicine, in The Netherlands, evaluated pharmacologic methods of OA pain management and their recent advances at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, UK.
Osteoarthritis is characterized by a vicious cycle of inflammation and cartilage degradation--one leads to the other, said van Weeren, and there is no cure. Veterinarians can manage affected horses' pain, however, using either systemic or local treatments.
Systemic Treatment of Joint Pain
NSAIDs are the most important and commonly used pain relievers. They work by inhibiting the enzyme cyclooxygenase (COX) and impeding production of pro-inflammatory molecules called prostaglandins. Most traditional NSAIDs inhibit both COX-1 and COX-2 enzymes (COX-2 causes inflammation and pain in the body, while COX-1 is associated with beneficial functions such as protecting mucosal barriers in the gut), whereas newer NSAIDs are "more selective COX-2 inhibitors and have a superior gastrointestinal safety profile," said van Weeren.
Phenylbutazone (Bute) is the most commonly used NSAID, and it's highly effective as well as inexpensive, said van Weeren. However, he added, its effect on cartilage is questionable, it has a narrow safety margin, and it might cause gastric ulcer development. "Although proven effective, comparative research on clinical efficacy vs. other NSAIDs in horses is limited, and information on the effects on the primary disease process is even scarcer and conflicting," he explained.
Flunixin (Banamine) is primarily used for treating abdominal pain, but is also effective for treating lameness. Veterinarians consider it to be safe to handle as well.
Meloxicam (Metacam), a COX-2 inhibitor, is the only NSAID with data on its in vivo (in the live horse) effects on cartilage, said van Weeren, indicating it not only helps reduce acute joint inflammation, but also has a mitigating effect on the inflammation-induced damage to the cartilage.
Local Treatment of Joint Pain
Local treatment mainly consists of intra-articular (IA) corticosteroids, which inhibit inflammation and can affect cartilage turnover and repair. "Intra-articular corticosteroid use has been controversial because of the deleterious effects of frequent long-term use on cartilage integrity, but now there is agreement that, if used judiciously with respect to frequency, interval, and dose, the benefits outweigh the disadvantages," said van Weeren.
Methylprednisolone acetate is a long-acting corticosteroid that has a clear anti-inflammatory effect with still preserving the normal joint environment.
Betamethasone acetate is a medium- to long-acting corticosteroid; however, researchers have observed in vitro (in the lab) evidence of a detrimental effect on the cartilage.
Triamcinolone acetate has a medium duration of action, but is one of the most widely used corticosteroids. "In vitro studies indicated it may potentially suppress inflammation without negative effects on the transcription of extracellular matrix (in articular cartilage, comprised of type II collagen, proteoglycans, and water) genes," van Weeren explained.
Opioids such as morphine are used frequently in humans to control post-operative pain. These have shown a significant effect on lameness, joint effusion, and behavioral signs of pain but are still in their experimental stage.
After discussing each of these pain relievers, van Weeren pointed to intra-articular opioids as a new and promising treatment. Other analgesics on the horizon include new gel-like biomaterials and nanoparticles or microspheres that can be used as carriers for drugs "to get a (controlled) prolonged release of the drug in the joint after a single injection, avoiding long-term use of much higher oral doses," he said.
"Pain relief alone may have a favorable (short- to medium-term) clinical effect, but could potentially also have adverse effects on the underlying disease process and long-term outcome," he concluded. Owners should work with their veterinarians to use these drugs judiciously and determine what works best for each individual horse.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.