FEATURE DENIS BLAKE
Gabapentin in Horses Gabapentin does have clinically useful applications in horses. Like humans, horses may experience neuropathic pain, and there are a handful of reports about its beneficial use. Neuropathic pain is caused by abnormal neural stimulation rather than from inflammation and therefore does not respond to anti-inflammatory drugs (e.g., phenylbutazone, flunixin). Specifically, horses may be treated with gabapentin subsequent to nerve injury and laminitis, conditions associated with neuropathy. Most significantly, the inflammation from a preexisting bone injury would not respond to treatment with gabapentin. The dose recommendations range from 2.5 mg/kg to 20 mg/kg orally once to twice per day. Similar to humans, the effective plasma concentration of gabapentin in horses is in the range of 10 micrograms per milliliter (10,000 nanograms per milliliter).
Gabapentin Positives in Horse Racing Our first notice of a gabapentin positive occurred in 2018 when a horse running at Charles Town Races in West Virginia showed a gabapentin identification of about 3 nanograms per milliliter (ng/ml) in serum and 86 ng/ml in urine. It turned out the source of gabapentin in this matter was inadvertent transfer from the horse’s groom, who had been prescribed the medication for diabetic neuropathy. No split sample analysis was performed, given that the history of the case showed that the groom involved was being prescribed 2,000 milli46
grams a day of gabapentin. The good news is that these events were considered mitigating circumstances by the stewards and the trainer was not fined or suspended, although there was a loss of purse. To the best of our recollection, there has been a small number of similar gabapentin identifications at Charles Town, all following the same general pattern with the penalties imposed recognizing the mitigating circumstances and generally involving a simple withholding of the purse with—and this is important—generally no medication penalty points awarded against the trainers. The next sequence of gabapentin events brought to our attention was the occurrence of an apparently ongoing sequence of gabapentin identifications in Ohio. To the best of our knowledge, the first Ohio gabapentin positive was called on January 6, 2018, at Northfield Park (a harness track), followed by two more, one on October 23 in blood and urine and another on November 18 in blood only. Another positive was called on November 19 at Mahoning Valley Race Course, the only, to our knowledge, gabapentin identification at an Ohio Thoroughbred track. Then, in 2019, this Ohio gabapentin identification pattern recommenced, starting on May 25 and totaling six identifications at the Scioto Downs harness track. Additionally, between August 21 and September 27, there were 10 gabapentin identifications at Ohio county fair tracks and two other identifications at Northfield Park on August 16 and September 11 for a reported total of 18 gabapentin identifications that year in Ohio racing. While the penalties imposed were generally a 15-day suspension, a $500 fine and loss of purse, the apparently random, unavoidable and completely unknown origins of these identifications led to a request by the Ohio Harness Horsemen’s Association for us to review the situation. Our review began with an analysis of the Association of Racing Commissioners International (ARCI) records on gabapentin identifications in U.S. racing, which showed the sequence of gabapentin identifications as set forth in Figure 1. The first ARCI-listed gabapentin identifications were four cases in 2009 in California. Next, in 2014, was one case in Oklahoma. In 2015, there was one case each in North Dakota, Indiana and Illinois. In 2016, there was one case in a Thoroughbred in West Virginia. In 2017, there were two cases in New Mexico and one case each in Arizona and Massachusetts. The year 2018 shows seven cases: three in Ohio and two each in West Virginia and Indiana. For 2019, there were 17 cases reported, including eight cases in Ohio (plus another 10 called in that state but not yet adjudicated/reported). The other nine cases in 2019 include one in Florida, two in California and three each in Kentucky and West Virginia. For 2020 to date, there has been one case each in West Virginia and New Jersey. Testing for gabapentin in Ohio was remarkably productive, with a total of 22 cases called, accounting for half and then some of the total of U.S. gabapentin identifications. The Ohio cases started with three reported (and at least one not yet added to the database) in 2018, with the identifications apparently in both blood and urine. In 2019, there were 18 reported identifications, all in blood, but that September, the Ohio gabapentin identifications abruptly stopped and no further identifications have been reported to date. The ARCI data records four cases as being associated with inadvertent human exposure. Of these four cases, two arise from Hoosier Park, and two come from Charles Town. Given their low concentrations and apparently inadvertent origins, the usual penalty for a gabapentin identification has been a $500 fine and a 15-day suspension with loss of purse. A recent exception was the Sadler matter in California; he was fined $15,000 and suspended for 60 days, 45 of which were stayed with a probationary license as long as he received no further medication violations. However, we must note that the Sadler ruling covered two gabapentin identifications and one for clenbuterol, so this ruling was not based on a single gabapentin identification. As shown at the beginning of the article, the apparent source of the gabapentin in the two Sadler horses was inadvertent transfer from a groom who had been prescribed gabapentin, just as in the THE HORSEMEN’S JOURNAL
FALL 2020