Introduction: Robaxin 500mg
Robaxin 500mg: Exertional rhabdomyolysis (ER) is a form of exertional myopathy in horses that is represented by muscle fatigue, pain, or cramping associated with exercise.
Less common exertional myopathies that cause exercise intolerance without muscle necrosis include mitochondrial myopathies and forms of polysaccharide storage myopathy in Warmblood horses.
1 While exertional rhabdomyolysis was once considered a single disease described as azoturia, tying-up, or cording up, it is now known to comprise several different myopathies which differ significantly in etiopathology despite similarities in clinical presentation.
2 Exertional rhabdomyolysis can be sporadic (with single or very infrequent episodes), or chronic (with repeated episodes occurring).
Any breed of horse can develop sporadic exertional rhabdomyolysis. The most common cause is exercise that exceeds the horse’s state of training.
The incidence of muscle stiffness also has been found to increase during an outbreak of respiratory disease.
Dietary deficiencies of sodium, vitamin E, selenium, or a calcium-phosphorus imbalance can also contribute to this condition.
Some horses have recurrent episodes of rhabdomyolysis even with light exercise, which is known as chronic exertional rhabdomyolysis.
Diagnosis of Exertional Rhabdomyolysis in the Horse
Approximately 3% of exercising horses are reported to have had an episode of ER in the last 12 months.3 Clinical signs of exertional rhabdomyolysis are usually are seen shortly after the onset of exercise.
Horses with ER usually show signs of muscle stiffness, shifting hindlimb lameness, elevated respiratory rate, sweating, firm painful hindquarter muscles and reluctance to move that can last for several hours. Subclinical episodes can occur in some horses, causing decreased performance and painful muscles without other overt signs.
A diagnosis of ER is usually based on clinical signs of muscle stiffness and pain after exercise in conjunction with elevations in serum creatine kinase (CK) and aspartate transaminase (AST) activities.
The degree of elevation of these enzymes in serum is dependent on the severity of muscle damage as well as the length of time that has elapsed between the sample collection and the occurrence of muscle
Severe exertional rhabdomyolysis can lead to renal compromise due to ischemia and the combined nephrotoxic effects of myoglobinuria, dehydration, and NSAID therapy.
In horses with hemoconcentration or myoglobinuria, a top priority will be to reestablish fluid balance and induce
diuresis. In severely affected animals, regular monitoring of BUN and/or serum creatinine is advised.1,2
Robaxin 500mg for Treating ER in Horses
Robaxin 500mg is a centrally-acting muscle relaxant that is n FDA-approved for use in horses as adjunctive treatment for acute inflammatory and traumatic conditions of skeletal muscle and for reduction of muscular spasms.
“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.2,4 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.
Methocarbamol is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies.
METHOCARBAMOL 500 MG/ML oral paste by NexGen Pharmaceuticals is an excellent choice for the treatment of various muscle-related conditions in horses, including tie-up (ER) prevention, muscle soreness, trauma, bursitis and other conditions that can cause painful muscle spasms.
Robaxin 500mg (Methocarbamol) carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.