Nitroglycerine for Laminitis: Use Caution

Walk down the aisle of any vet clinic, and you're sure to see a foundered horse. Whether an acute case in treatment or a chronic case having some remedial shoeing therapy, every clinic has its pet cases...or should we call them survivors? For every "old chronic case" which revisits a veterinary clinic periodically, how many have been destroyed? This summer, the great race mare Bayakoa succumbed to laminitis. She, who was famous for throwing two shoes in one race without missing a stride, was no match for the assault of laminitis. The disease's most famous victim, of course, was Secretariat.

Hoofcare & Lameness/R. F. Redden, DVM

Nitroglycerine patches come in several dosages, sizes, and shapes. How much to use and how often to replace them are large variables.

Research is going on around the world to ascertain the systemic causes of this crippling disease. From Australia, Chris Pollitt, MRCVS, tells us that laminitis is a breakdown of the basement membranes surrounding the secondary lamellae that are the "hand in the glove" that attach outer hoof wall to inner bone. Pollitt has been able to isolate enzymatic agents that he feels are released like a gang of thugs bent on wreaking havoc in the foot. His research now focuses on finding anti-enzyme agents, very similar to the process used to fight cancer such as malignant melanoma (skin cancer). Pollitt suggested that a patch might someday be applied in the coronet area, releasing whatever agent into the foot.

In 1996, the Equine Veterinary Journal published the first article on the experimental use of glyceryl trinitrate cream on the shaved pasterns of 15 grass-foundered ponies. The study was conducted at the University of Sheffield in Britain. Primary researchers were all from the University's Institute of Endocrinology.

The cream reduced lameness and the classic bounding pulse. Two ponies not treated with the cream continued to deteriorate. A second substance, L-arginine given intravenously, was noticed to increase rapidly the blood flow to the foot, while decreasing the blood pressure.

Sending a rapid blood flow to the foot of a sick animal is a major undertaking, and not without potential complications. Careful monitoring of blood pressure and heart rate is important. Rapid perfusion of blood to injured tissue can be very painful for the animal, and anti-inflammatory drugs might be needed. The researchers stated that they saw the drugs as helpful in the acute stage of laminitis.

What the researchers didn't say in their report is that nitroglycerine is a potent agent that easily can be absorbed by humans who come into contact with it. Naturally, casual experimentation with the drug has begun in the United States, and Ric Redden, DVM, of Kentucky reports severe frustration, and personal risk, while working on a horse which had been treated with the cream. He stated that he double-gloved his hands and still felt an almost immediate severe headache. Since nitroglycerine is used on humans to stimulate the heart, this drug should not be used by anyone with a heart condition.

Pollitt, writing from the University of Queensland in Australia, offers this explanation of how and why nitroglycerine might have an effect on laminitis:

"Nitric oxide (NO) is now known to be the universal and most potent of the body's (horse or man) natural vasodilators. It is manufactured from argenine, a simple amino acid, by all the cells lining all blood vessels (the endothelial cells). GTN (glyceryl tri-nitrate or nitroglycerine) acts as a source of nitric oxide and acts very quickly to dilate. Pills of GTN are the famous heart pills (to reverse the ischemia of angina) so beloved of movie directors when the beautiful young bride snatches the pills from the outstretched hands of her aging but fabulously rich husband.

"When endothelial cells are being ravaged by an episode of septic shock or endotoxemia, they have a tendency to give up their NO and cause a rapid fall in blood pressure (terminal, irreversible shock). When horses sick with colic reach this stage, their mucous membranes go bright red, then they die. Horses with carbohydrate overload are also endotoxic, and it is my hunch that the vasodilation that always coincides with the development of anatomical destruction of the lamellae is mediated by NO. This is speculation on my part.

"If I am right it means that vasodilators like NO are contraindicated during the fever, developmental, stage of laminitis. I have no problem with GTN patches, along with other vasodilators like isoxuprine and ACP, when the metabolic crisis is over and the foot is trying to heal."

One California farrier saw the patches used on a miniature horse which had suffered repeated bouts of acute laminitis. The patches were credited with swift recovery. When the horse was sent home, it was accidentally overfed, relapsed, and the owner applied additional patches and averted more disaster. Nitroglycerine patches come in several dosages, sizes, and shapes. How much to use and how often to replace them are large variables. The skin can become inflamed when the stronger patches are used.

Texas farrier Burney Chapman, known for his successful treatment of laminitis with the use of heartbar shoes, reports that he has been working on foundered and injured horses treated with the patches for about 16 months. He believes that the patches were very helpful, both to acute and chronic cases, and to horses suffering from coronary band lacerations and even navicular-type lameness. Chapman has a high rate of success even without the patches, and his enthusiasm for including them in the treatment regimen is spreading across the United States.

However, like everyone else who has observed this phenomenon, Chapman doesn't have any answer for how or why the patches work. He recommends the use of the rectangular patches over the round ones, and stresses that use of the patches is not a replacement for sound therapeutic shoeing used in conjunction with them.

Chapman's experience is that the patches are on both the pastern and the area between the bulbs of the heels; the patches are held on with vet wrap tape and the caregiver must be sure to wear rubber gloves. The patch is left in place for 8-10 hours, then repeated, then removed for a period of 8-10 hours. The medication is administered in a "time release" fashion. Burney said that he has seen the patches used on several breeds of light horses, but not on any warmblood or draft breeds.

Rob Sigafoos, CJF, of the University of Pennsylvania's New Bolton Center, also has experience with horses treated with the patches; his comments were encouraging, although he mentioned that the patches should not be used on horses with endotoxemic episodes.

Tom Goetz, DVM, of the University of Illinois at Urbana-Champaign, also gave the potential for this type of product a big thumbs up. As with any new treatment that has not been fully researched, the patches will need to be used with extreme caution until studies show that they really do have an effect when used without expert shoeing and other medication. Manufacturers will need to correlate body weight and dosage and application sites for horses of different sizes, and calculate side effects.

"It's very promising, and very interesting," Goetz concluded. "Just as an experiment, I used them on a chronic case, and they really did seem to improve. Was it a coincidence? I really can't say. But I am optimistic that this may be something that can, and will, help us treat these horses."


"Nitric Oxide and equine laminitis: topical speculation or scientific fact," in Equine Veterinary Journal.

"Nitric Oxide donors as treatment for grass induced acute laminitis in ponies," by K.A. Hinckley et all, in Equine Veterinary Journal.

"Nitric Oxide: Friend or Foe," by Clare Bryant and J. Elliott, in Equine Veterinary Education (1994).

Quarter Horse Journal, November 1996 and subsequent editions related to the treatment of world-record holder Evening Snow with nitroglycerine patches.

About the Author

Fran Jurga

Fran Jurga is the publisher of Hoofcare & Lameness, The Journal of Equine Foot Science, based in Gloucester, Mass., and Hoofcare Online, an electronic newsletter accessible at Her work also includes promoting lameness-related research and information for practical use by farriers, veterinarians, and horse owners. Jurga authored Understanding The Equine Foot, published by Eclipse Press and available at or by calling 800/582-5604.

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