New Topical Osteoarthritis Treatment Available

The FDA recently approved a new non-steroidal anti-inflammatory drug (NSAID) that can be applied to the skin over a horse's joint to relieve pain of osteoarthritis. The approval represents the first topical equine pharmaceutical formulation of a compound called diclofenac that uses liposome technology--which allows medication to be absorbed straight to the site of the horse’s joint problem. This provides a new option for practitioners treating with NSAIDs, since a disadvantage of systemic NSAID use is that it has been shown to increase risk of gastrointestinal or renal toxicity.

The product, developed by IDEXX pharmaceuticals, is called SURPASS, and it will be available by veterinary prescription only.

Diclofenac has been used in humans for relief of pain and inflammation, and it has been available for oral, intravenous, intramuscular, intracolon, rectal, and topical administration. The drug is designed to inhibit cyclooxygenase activity and prostaglandin biosynthesis. Cyclooxygenase is an enzyme that directs production of prostaglandins, which are chemical substances that cause inflammation by increasing blood flow to the damaged tissue, make blood vessels more "leaky," and produce pain in inflamed tissue. Therefore, the medication serves as a potent anti-inflammatory that acts as an analgesic (reduces pain) and antipyretic (reduces fever).

SURPASS is labeled for the treatment of equine osteoarthritis of the carpus (knee), tarsus (hock), fetlock, and pastern.

Joseph J. Bertone, DVM, MS, Dipl. ACVIM, now professor of equine medicine in the College of Veterinary Medicine at the Western University of Health Sciences, presented information on SURPASS field studies at the 2002 American Association of Equine Practitioners Convention in Orlando, Fla., while the drug was still under development. (Bertone was practicing with Alpine Animal Hospital in Carbondale, Colo., at the time of the presentation.)

Bertone and collaborators wrote in the study, "Liposomes are microscopic vesicles composed of membrane-like lipid layers surrounding a compartment. The lipid layers are made up of phospholipids that have a hydrophilic (readily interacting with water) head and a lipophilic (having an affinity for fat) tail. Liposomes penetrate the skin, carrying their content," in this case diclofenac.

"They are used as slow-release vehicles or to target or localize a drug to a specific site," added the researchers. "They provide enhanced penetration and sustained release when compared with conventional topical products."

In Bertone's study, 60 horses received SURPASS, 56 horses received a placebo, and both groups were scored on the basis of pain, lameness, and joint mobility before, during, and after treatment with either SURPASS or the placebo. Following treatment, there were significant differences in investigator scores of lameness and pain (these horses improved), and owner evaluation of improvement in horses receiving SURPASS. Improvements in joint mobility were not statistically significant.

"Three of the four lameness indicators evaluated in the study had a statistically significant improvement with diclofenac treatment," wrote the authors. Statistically significant improvements were noted in hocks alone, fetlocks alone, and fetlocks and pasterns together.

The authors added, "When a joint lameness can be treated safely and effectively with local therapy, this route is preferable to administration by systemic routes."

Another study designed to detect absorption of SURPASS completed at the University of Georgia found that the medication was "readily absorbed transdermally and may be efficacious for reducting subcutaneous inflammation in horses."

According to Rob Keene, DVM, equine professional services veterinarian at IDEXX, "The Georgia study shows that diclofenac gets through the horse’s skin and reduces inflammatory mediators. The AAEP abstract (Bertone’s study) shows that SURPASS is clinically effective.

"Rather than treating the whole horse with potentially harmful NSAIDs like phenylbutazone, with this drug, if your veterinarian diagnoses osteoarthritis in the hock joint of the horse, we know that application of SURPASS will significantly improve lameness scores."

Jim Mitchell, DVM, an associate with John R. Steele and Associates in Cream Ridge, N.J., treats harness horses and hunter jumpers. He performed some of the field trials using Surpass. "We did 12 cases in the study--most were knees, one hock, one ankle--and we had a really positive experience with the drug," said Mitchell. "I was disappointed that it took so long to get it approved. I will definitely use it when it comes available."

Safety of SURPASS
"Because we believe that it is locally enhanced, the chances of systemic side effects at the recommended dose are minimal," said Keene. "If we compare 2 g of Bute, which is 2,000 mg given systemically, versus the 73 mg of diclofenac applied directly, the data shows this approach to therapy to be very safe."

"Diclofenac is a potent anti-inflammatory drug and some is going to be absorbed systemically," he added. "If you exceed recommended dose levels, you could see side effects typical of other NSAIDs."

IDEXX performed target animal safety studies, in which six horses were given SURPASS twice a day at up to 5.6 times the recommended dose for 14 days; and six horses were given 2.8 times the recommended dose for 28 days. One horse in the 5.6 times the recommended dose group developed a gastric ulcer. Four of six in that group lost weight during the study. In the 2.8 times higher group, one horse developed diarrhea and uterine discharge.

In the efficacy studies completed by Bertone and colleagues, one diclofenac horse developed colic on Day 4 of the study, but both the treating practitioner and the study investigator believed it was not caused by the drug.

Finally, in the Georgia study, no adverse events were noted on blood tests, and no adverse experiences were noted that could be attributed to the treatment.

The recommended dose of SURPASS is a five-inch ribbon of the ointment applied over the affected joint twice a day for up to 10 days. Veterinarians and horse owners should wear gloves while applying it. Keene added that SURPASS should not be mixed with any other medications or agents on the area to be treated.

The company is in the process of evaluating the status of SURPASS on drug tests and determining a recommended withdrawal time before competitions. According to IDEXX, the cost of SURPASS to horse owner should be comparable to most other osteoarthritis or lameness-type products.


About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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