One of the most potentially damaging drugs to hit the racetrack in recent years is erythropoietin, or EPO. A synthetic version of a naturally-occurring hormone which stimulates the bone marrow to make more red blood cells, EPO was designed to treat anemia in human chemotherapy patients, and those with severe renal disease.  It was considered a medical breakthrough when it was introduced in the 1980’s, and is still a valuable part of the drug arsenal for these conditions, with sales in the billions of dollars in 2002.

Unfortunately it wasn’t long before human athletes noticed the potential of EPO for performance enhancement. Cyclists, swimmers, and long-distance runners reasoned that more oxygen in the tissues meant more endurance–and the results bore them out, with an estimated 10-15% performance boost. But EPO administered to a human athlete prompts the release of so many red blood cells (RBCs) that the blood becomes thick and sludgy (a condition called polycythemia), and that may set athletes up for blood clots, strokes, and heart attacks. It’s estimated that EPO was a factor in the deaths of at least 15 European cyclists in the 1980s and 90s, and EPO scandals have plagued the Tour de France bicycle race and several Olympic events in the past decade or so.

In theory, EPO ought to work as a performance-enhancer in horses for the same reasons it does so in human athletes, but there’s some debate as to whether the drug actually functions this way in equines. Because horses are "natural blood dopers," with spleens that have the unique ability to dump up to 12 liters of extra RBCs into the bloodstream at times of stress, how much EPO might increase–or over-ride–their natural splenic contraction is a major question mark.

Furthermore, dangerous allergic reactions and severe, often fatal anemia are two significant, documented risks of administering EPO to horses. And for horses already being given diuretics, such as Lasix, the ‘sludging effect’ of the cocktail could be potentially lethal.

Stan Bergstein, the executive vice-president of Harness Tracks of America, doesn’t mince words when it comes to EPO. "It’s extremely dangerous from my perspective," he says. "The sludging of the blood is so ominous that any trainers using this drug have no regard for their animals, in my opinion. It subjects the horse to stroke and the danger of falling in a race–which is a danger not only to that horse, but also to the other horses racing all around them."

EPO has become a popular drug on the backstretch partly because it’s difficult to detect and clears the system rapidly. The half-life of EPO in a horse’s system is only minutes or hours, while its effects (increased levels of RBCs) may last for up to four months. At the track, a horse may have had EPO administered many days or weeks prior to a standard post-race visit to the test barn. And because the drug’s effects mimic the natural splenic response, measuring the haematocrit (the level of RBCs in the blood) is also ineffective.

Regulatory bodies, therefore, have pinned their hopes on a different approach: a test for EPO antibodies in the blood, rather than the actual drug itself. Because injectable EPO is actually a human recombinant version of the hormone, it’s slightly different than the equine version, and thus is recognized as ‘foreign’ by the horse’s immune system. Over time, he will build up antibodies, which reach measurable levels after about three injections’ worth, researchers say. The advantage of measuring antibodies is that they linger in the system for far longer than does the drug itself.

Steven Barker, MSc, PhD, state chemist to the Louisiana Racing Commission, and a professor in the Department of Comparative Biomedical Sciences at Louisiana State University’s School of Veterinary Medicine, has been running EPO antibody tests for approximately three years now. He notes that about 19 out of every 100 tests in Louisiana produce a "suspicious" response to the antibody test, similar to those noted in horses known to have been given EPO. But, he says, a positive test is not necessarily an indication that the horse was given EPO recently. "Any horse who’s had EPO might have a positive antibody response for its entire life–we really don’t know how long the titer stays elevated." In an industry where horses sometimes change hands frequently, this can make it difficult to pinpoint whether the current handlers are guilty when a horse tests positive.

Furthermore, says Barker, "Some horses just don’t mount an antibody response to the drug, and we don’t know how common that is. Overall, I’d say the test has less than 40% accuracy. But it’s the best we’ve got right now."

Researchers at the Pennsylvania Equine Toxicology and Research Laboratory (PETRL) at the University of Pennsylvania are currently working on the development of a test which will confirm the results of the EPO antibody test. "At the moment we can’t confirm (a positive test)," says Barker, "which limits the sanctions we can take against trainers or owners." In most racing jurisdictions now testing for EPO, punishments are limited to warnings or the reversal of claims. "We need something more sensitive which can detect the drug for a longer period of time after administration."

Because of the way EPO is administered and metabolized over time, drug testing would also be far more effective if it were to be performed on a random basis instead of just post-race. "(Random testing) would be the easiest way to catch them," says Barker. "It’s the norm for human athletes in many sports, so why not racing? Basically it’s a problem of logistics and funding at this point."

Regardless of all these snags, EPO testing appears to be having an impact. In Ontario, for example, 16,250 horses were tested for the drug (and a related substance, darbopoeitin) from November 2003 to April 2004, with six positives noted in that time, all Standardbreds. Three of the positive tests were observed in November, one each in December, January, and February, and there have been none since that time. Barker says he’s seen similar results in the Louisiana racing jurisdiction. "There was an initial flurry of positive tests, but significantly fewer since then. That’s the way it often works–as soon as there’s a test, the drug tends to disappear.

"But that always makes me worry about what they’ve moved on to," he added.