As states work their way through updated medication rules, one of the therapeutic medications that seems to garner repeated discussion is the corticosteroid methylprednisolone acetate, sold as Depo-Medrol. New York officials issued a statement warning horsemen and veterinarians not to use the drug at all in late 2014, and authorities in West Virginia sent an advisory about the cut-off time for using the corticosteroid pre-race. Horsemen there had been coming up with drug overages despite following the state's suggested three-week withdrawal guideline.
To understand why Depo-Medrol is getting more attention than the other corticosteroids used on the racetrack, it's important to understand how this class of drugs works.
The synthetic corticosteroids that are injected into a horse's body are cousins of the corticosteroids found in horses (and humans) that spike in response to fear or stress. They also reduce inflammation, which makes them a good tool for a veterinarian looking to treat an issue in the joint. A reduction in inflammation is often good for the joint's health—severe inflammation depletes the cartilage and the joint fluids, so when used properly, a corticosteroid can quiet the joint's reaction while a veterinarian treats the underlying cause of the pain.
“They're very effective at helping the interior of the joint. If you put them in, they do their job and get gone,” said Dr. Larry Bramlage, surgeon at Rood and Riddle Equine Hospital.
The downside to placing a corticosteroid into a joint is that it freezes everything—including the production of hyaluronic acid and polyglycan, substances that keep the joint protected and fluid. In the short-term, this isn't much of a problem; the joint has a reserve of these substances and once the steroid clears, the production returns to normal. With repeated re-introduction of the corticosteroid, however, that process gets too far behind and there is potential for damage to the cartilage.
Depo-Medrol packs an especially big punch compared to other drugs in its family. Synthetic corticosteroids are crystallized to increase their duration of effect, and the absorbability of a given corticosteroid's crystals determines how long the drug lasts in the joint. Depo-Medrol's crystals last an especially long time compared to other corticosteroids, which is by design.
“It can be an advantage in situations where you need a long-acting corticosteroid, but in the joint, you generally don't want a huge, long duration,” said Bramlage, who said this was especially true for high-motion joints such as knees and ankles.
Depo-Medrol is also significantly more concentrated than other corticosteroids, and Bramlage is concerned that many practitioners don't realize just how much. Most commercially-available Depo-Medrol is packaged in a concentration of 40 milligrams per milliliter. Triamcinolone and betamethasone, by contrast, are six milligrams per milliliter.
“People think in mls,” said Bramlage. “'I just put 1 ml in the joint.' Well, with Depo- Medrol that's a huge amount of steroid and it lasts a long time.
“It's sort of like drying your clothes with a blowtorch; if you get it just right, you're okay, but if you overdo it a little bit, you're in trouble.”
Depo's longer acting time could also explain some of the struggles states have had with unintentional overages, although that's dependent upon the dose a veterinarian elects to give a horse. Experimentally, Bramlage said Depo-Medrol is usually out of the horse's system in three weeks, though it has sometimes been found as long as 70 days after administration.
If you're wondering whether overuse of corticosteroids is responsible for the recent decline in starts per year, Bramlage says think again.
“That's a common fallacy,” he said. “Thirty percent of the starts in the U.S. are made by horses that are five years old and older, and that's consistent over 30 years. So successful older horses are staying in the population.”
Instead, Bramlage believes the drop in starts has more to do with the success of those individual horses and an inability of the owner to keep a horse running through more than a few unprofitable starts.
However, Bramlage said that being tough on Depo-Medrol usage is a good thing. He can tell when he's operating on a horse that has had repeated Depo-Medrol injections—the cartilage takes on a softer, yellow appearance and feel. Depo-Medrol makes it very hard to monitor a horse's joint condition.
The use of a highly concentrated long-acting steroid like Depo-Medrol doesn't just leave a horse at risk for cartilage damage. It also inhibits the veterinarian and the trainer from gauging whether the underlying cause of the inflammation has actually improved, as a horse doesn't get a chance to rebound from repeated Depo-Medrol administration like he would between repeated administrations of a short-term corticosteroid into his joints.
“You hear lots of complaints that the new corticosteroid regulations virtually eliminate the ability to use Depo-Medrol in the actively racing horse,” he said, although he pointed out it's possible if veterinarians use smaller doses less frequently. “That's true, but in my opinion, it's not all a bad thing. It makes the joint easier to follow. You have to think of that lameness as a sign of a problem, not as the problem.”
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