Methocarbamol 5 gm/scoop, Oral Powder, 100 Scoops (20cc Scoop)
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Recurrent muscle pain and stiffness with exercise occurs in many breeds of horses. The terms Monday Morning Disease, Azoturia, tying-up, chronic intermittent rhabdomyolysis and recurrent exertional rhabdomyolysis (ER or RER) have all been used to describe this syndrome. Numerous causes for these have been proposed over the years, including hypothyroidism, electrolyte depletion, lactic acidosis, glycogen storage disorders and altered muscle contractility.1 In most cases, the entire collection of symptoms is typically referenced as exertional rhabdomyolysis (ER) whether it is recurrent or sporadic.
Thoroughbred horses are particularly susceptible to ER, with 5-10 % of all Thoroughbreds developing ER during a racing season.2 There is strong evidence from studies that susceptibility to ER has an underlying genetic basis; however the genetic model and pattern of inheritance has not yet been conclusively defined.3
Symptoms of ER in the Horse
Symptoms of exertional rhabdomyolysis usually present shortly after horses start to exercise or when resting post-exercise. These include:
- Muscle spasms
- Excessive sweating
- Rapid heart beat
- Rapid breathing
- Refusal to move
- Painful, firm muscles in the low back and rump
- Discolored urine
Sporadic Exertional Rhabdomyolysis
Horses of any age or breed can develop sporadic ER. Common causes include overexertion, muscle trauma, nutritional or electrolyte imbalances and fatigue. It has been reported that horses participating in endurance competitions on hot, humid days are more susceptible to sporadic ER due to high body temperatures, insufficient fluids and electrolytes and depleted energy stores. For the management of horses with sporadic ER, equine veterinarians often recommend rest, fresh water and tranquilizers or NSAIDS. Supplementing a horse’s diet with sodium, selenium and vitamin E is also helpful.3
Recurrent Exertional Rhabdomyolysis
There is anecdotal evidence that horses with nervous personalities experience more episodes of recurrent or chronic ER, although it is far more common in Thoroughbreds and Quarter Horses.3 Stress seems to induce the condition in certain instances. In addition to an assessment by an equine veterinarian, a balanced diet and an adequate intake of minerals and vitamins are helpful in managing recurrent ER.1
Methocarbamol for Exertional Rhabdomyolysis in Horses
Methocarbamol is a centrally-acting muscle relaxant that is n FDA-approved for use in horses (IV only; other forms are extra-label) as adjunctive treatment for acute inflammatory and traumatic conditions of skeletal muscle and for reduction of muscular spasms.4
“In horses, oral paste bioavailability is ≈50%; volume of distribution is 1.6 L/kg, clearance is 6 to 9 mL/kg/minute, and elimination half-life is 3 to 4 hours. In a study, the elimination half-life for single 5-g and 15-g oral (paste) doses were 32 and 3.7 hours, respectively, and there was no significant difference between the single dose of 15 g and multiple doses of 15 g (4.1 hours). The majority of horses given a single oral dose or multiple oral doses of 15 g were above the regulatory threshold set by the Association of Racing Commissioners International (ARCI) at the recommended withdrawal time.”4
Contraindications include food animals, animals with renal disease (injectable forms), and animals with a hypersensitivity to methocarbamol.3,4 Adverse effects can include sedation, salivation, emesis, lethargy, weakness and ataxia.
NOTE: The Association of Racing Commissioners International Uniform Classification Guidelines for Foreign Substances has designated methocarbamol a CLASS 4 DRUG.
Where to buy Methocarbamol
Methocarbamol is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. METHOCARBAMOL 5GM/SCOOP by NexGen Pharmaceuticals is an excellent choice for the treatment of exertional rhabdomyolysis (ER), muscle soreness, trauma, bursitis, muscle and ligament damage and other conditions that can cause painful muscle spasms in horses.
Methocarbamol carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.
FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.
1Valberg, S., et. al. Exertional rhabdomyolysis in Quarter Horses and Thoroughbreds: one syndrome, multiple aetiologies. Equine Exercise Physiology 5 Equine vet. J., Suppl. 30 (1999) 533-538.
2Fritz, K.L., et. al. (2012), Genetic mapping of recurrent exertional rhabdomyolysis in a population of North American Thoroughbreds. Animal Genetics, 43: 730–738.
4Plumb’s Veterinary Drugs.