It has been the hot topic of forums and Facebook over the last few weeks. Last month, the Food and Drug Administration sent cease and desist letters to multiple companies who are manufacturing or distributing medications in the United States that are labelled for the treatment of gastric ulcers in horses. These medications do not have FDA approval for these label claims, and therefore cannot be sold in the US with such claims.

What’s the big deal, you may say? Maybe you have used some of these omeprazole pastes or powders on your horses, and felt liked they worked for your horse. Or you have used Prilosec OTC or other generic tablets from the pharmacy, and they seem like they worked, too. Why is the FDA making such a big deal about this?

It’s been over 15 years ago now, but Merial introduced their proprietary omeprazole paste called GastroGard to the market in 1999. It is the first, and still the only, medication labelled for the treatment of gastric ulcers in horses in the United States. The medication itself is actually manufactured in Brazil for Merial.

Merial went through the safety and efficacy studies required by the FDA label to get the label for the treatment of gastric ulcers. The paste itself is 37 percent w/w (by water weight) omeprazole in each syringe – one syringe of GastroGard contains a total of 2.28 grams of omeprazole.

Omeprazole is an effective medication for actually healing gastric ulcers. Omeprazole is a gastric acid pump inhibitor – it works by binding itself irreversibly to an enzyme that regulates the final step in hydrogen ion production and blocks gastric acid secretion in the parietal cell of the stomach lining.

GastroGard – and any omeprazole medication for that matter – does NOT work by touching the stomach lining and magically healing the ulcers. Omeprazole needs to get into the small intestine, where the drug is absorbed into the blood stream. Once absorbed, it travels through the organs and blood vessels to get to the stomach lining cells, where it binds to the enzymes and inhibits gastric acid secretion.

Omeprazole uses a roundabout mechanism to heal stomach ulcers, not a direct one. So, we need to get omeprazole intact and whole to the small intestine in order for it to be absorbed and work.

Here’s the key – the omeprazole molecule is a very tricky compound to work with – it is very unstable compound, and gets inactivated when it is put into environments that it doesn’t like. One of the environments that inactivates it quickly is an acidic one – which your horse’s stomach is naturally full of, whether they have ulcers or not. One of the keys with omeprazole is that is needs to be delivered intact to the small intestine to be absorbed effectively – whether you are a horse, dog, or human, that is where omeprazole is absorbed.

This is pretty tricky to achieve in a horse. Before the days of GastroGard paste, veterinarians would try to use human labelled omeprazole tablets or capsules to achieve gastric ulcer healing. There were several issues with using capsules – first, in those days, it was really expensive. It would take over 100 of the 20mg capsules or tablets once daily to achieve the needed therapeutic amount of omeprazole.

Second was how to get 100-plus tablets into a horse – they would have to be crushed, or mixed with something, and even if you had one of those crazy horses that would eat tablets or capsules whole, tablets would still get crushed by the teeth of the horse.

It’s probably one of those things you didn’t know, but human omeprazole tablets and capsules have a special coating on them (hint – it’s purple!) that protects the inside of the tablet from being digested until it gets into the small intestine.

It’s pretty easy to get a human to swallow a tablet or capsule intact without interrupting the coating on the outside of the tablet, but a horse? Not so much. Every tablet or capsule that gets the outside coating crushed means that the omeprazole in that tablet will be rendered useless by the stomach acid before it even gets to where it needs to be in order to be absorbed.

Here’s where GastroGard shines – Merial developed a patented paste formula that protects the omeprazole suspended in its paste from being affected by being chewed, swallowed and digested in the stomach.

Their efficacy studies show that omeprazole given to a horse in their paste form reaches therapeutic plasma levels in the horse’s bloodstream. This is pretty impressive and really important when you are trying to heal gastric ulcers. Formulating and making this special paste base was and still is a very labor intensive and expensive proposition for Merial.

Now to address the elephant in the room – the cost. GastroGard has always been expensive, and continues to be considered one of the priciest medications for horses on the market today. Retail these days is approximately $34 for a single dose. Multiply that by 28 days of therapy and, well, it’s not hard to understand why people have been looking for a cost effective alternative.

Here’s the key – those off-label, cheaper omeprazole pastes and powders are not following any regulations at all. In the letters sent to the manufacturing and distributing companies last month, many of the products were tested and contained much less active omeprazole in the paste than the label claimed.

This could be because the omeprazole is unstable in the paste base, or it also could be because an unscrupulous company is not actually putting enough omeprazole in the paste or powder that they claim they are, to save on costs. This is why the FDA is, effectively, shutting down access to these products.

So what is the average horse owner to do? Now that you understand why using “real” GastroGard is so important in a horse if you want to heal a gastric ulcer, it may be a little easier to shell out the money for a product that you know will be effective because it gets to where it needs to be in order to be absorbed, and also contains the amount of drug stated on the label.

There are also coupons available through Merial to use if you buy GastroGard directly from your veterinarian, which may also help save on costs.

Tanis MacDonald Walker, DVM graduated from the Atlantic Veterinary College on Prince Edward Island and currently practices both small animal emergency and equine medicine in Delaware. You can email her attanis_macdonald@hotmail.com or visit her at www.drtanis.com. You can also write to her in care of InStride Edition.