Are Drugs Effective for Acute Laminitis?

Article by: Nancy S. Loving, DVM March 18 2009, Article # 13802

At the 2008 AAEP Convention, which was held Dec. 6-10 in San Diego, Calif., Bill Moyer, DVM, professor of sports medicine and head of the Department of Large Animal Clinical Sciences at the Texas A&M College of Veterinary Medicine and Biomedical Sciences, presented a variety of considerations on the state of medical treatment for laminitis. He stressed that once clinical signs are evident, damage has already been done: Pain and lameness are preceded by vascular and structural damage within the hoof laminae (lamellae).

So, he posed the question to the audience, "Is any specific medical treatment for acute laminitis efficacious in altering the outcome after a horse has developed clinical signs?"

Is any specific medical treatment for acute laminitis efficacious in altering the outcome after a horse has developed clinical signs?

The current consensus on effective therapy revolves around addressing and resolving the initiating cause(s) of laminitis. Other strategies attempt to alter blood flow in the foot, decrease inflammation, and avert endotoxemia. Moyer addressed these in his talk.

He explained that evidence is lacking about blood flow-altering agents having any effect on increasing laminar circulation. While use of digital nerve blocks might improve blood flow by inhibiting constriction of blood vessels, numbing the pain stops the horse from protecting his feet. Increased weight bearing exacerbates laminitis.

Acepromazine increases digital blood flow by direct action on vascular smooth muscle, but studies have not shown improvement in lamellar blood flow.

Isoxsuprene has vasodilating properties, while pentoxyfylline requires weeks of administration to decrease blood viscosity. It does this by acting on platelets to increase red blood cell flexibility. Both these medications are absorbed poorly when administered orally.

Nitroglycerin placed over digital blood vessels might increase blood flow, but it has not been shown to increase lamellar blood flow after the onset of clinical signs. Coupling this ineffectiveness with potential risks to the person handling the drug makes nitroglycerin a poor therapeutic choice. Heparin removes red blood cells from the system to decrease blood viscosity and thereby improve blood flow, but researchers have not examined its use in acute cases.

Inflammation is not always a component of laminitis, but when it is, non-steroidal anti-inflammatory drugs (NSAIDs) have been used. Moyer said there is humane justification for judicious use of NSAIDs, but one should be aware of downsides. Pain relief might increase mobility that exacerbates tearing of the lamellae.

Phenylbutazone (Bute) might reduce inflammation and pain, and it is affordable, but it does not prevent laminitis if given during the developmental stage and has not been shown to alter the course of acute cases.

Flunixin meglumine (Banamine) provides both anti-inflammatory and anti-endotoxin effects. However, if flunixin and phenylbutazone are given together, there is an increased risk of loss of serum protein, gastric ulcer disease, and/or colitis.

There is anecdotal support for use of dimethyl sulfoxide (DMSO) for its anti-inflammatory properties and ability to scavenge oxygen-derived free radicals, which form during hypoxia (deprivation of an adequate supply of oxygen) and reperfusion (restoration of blood flow to tissues following an incident or hypoxia). Damage can occur when blood flow is restored to tissues following an incident of reduced blood and oxygen supply. However, Moyer noted there is no evidence of hypoxia or reperfusion in this disease.

Anti-endotoxin drugs (flunixin meglumine, ketoprofen, and polymyxin B) might be warranted as there is an association between endotoxemia and the development of laminitis. Endotoxin causes insulin resistance with decreased use of glucose by the lamellar tissue. While they might not necessarily be effective in treatment of laminitis, anti-endotoxic drugs might be life-saving.

Moyer said caretakers and veterinarians should address environment and ground surface, housing, causes of obesity, and management of the foot itself. He recommends explaining to clients that the pathogenic mechanisms of laminitis are not well-understood and that a horse's clinical appearance might correlate with the outcome, but it is not always an accurate predictor due to potential for complications.

In general, controlled studies do not exist regarding the efficacy of various treatments for laminitis, and some therapies have additional risks beyond their failure to improve the situation.