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
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
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.