Page 900 - Adams and Stashak's Lameness in Horses, 7th Edition

866 Chapter 7

Table 7.2. Potential medications that can be used to treat acute rhabdomyolysis in the horse.
VetBooks.ir Category Drug Dose Comment

Tranquilizer
0.04–0.07 mg/kg IV
May be hypotensive; use caution if dehydrated
Acepromazine
Xylazine 0.4–0.8 mg/kg IV
Detomidine 0.02–0.04 mcg/kg IV
Butorphanol 0.01–0.04 mg/kg IV Use with xylazine/detomidine
Anti‐inflammatory Phenylbutazone 2.2–4.4 mg/kg IV or oral Use caution if dehydrated
Flunixin meglumine 1.1 mg/kg IV or oral Use caution if dehydrated

Ketoprofen 2.2 mg/kg IV Use caution if dehydrated
DMSO 1–2 mg/kg IV or oral Use as a solution diluted to less than 20%
Pain control: CRI Lidocaine 1.3 mg/kg IV followed by 0.05 mg/kg/min IV
Detomidine 0.22 mcg/kg IV followed by 0.1 mcg/kg/min IV
Butorphanol 13 mcg/kg/h

Muscle relaxant Methocarbamol 5–22 mg/kg IV slowly
Dantrolene 2–4 mg/kg oral QID

excellent sedation and analgesia. NSAIDs such as keto­ Etiology of Exertional Rhabdomyolysis
profen, phenylbutazone, or flunixin meglumine provide
Some horses develop exertional muscle damage as a
additional pain relief. Analgesic treatment is continued result of extrinsic nutritional or environmental factors.
to effect, but most horses are relatively pain free within
18–24 hours. For horses with extreme pain and distress, These sporadic cases of ER are usually amenable to
treatment once the extrinsic cause of muscle damage is
a constant rate infusion of detomidine, lidocaine, or
butorphanol can make the difference between adequate identified. Some horses, however, develop chronic ER,
and many of these cases are due to an intrinsic and
time for recovery and euthanasia.
Intravenous or intragastric dimethyl sulfoxide can inherited dysfunction of muscle metabolism or muscle
be used as an antioxidant, anti‐inflammatory, and contraction.
osmotic diuretic in severely affected horses. Muscle
relaxants such as methocarbamol seem to produce var­ Sporadic Exertional Rhabdomyolysis
iable results, possibly depending on the dosage used.
Dantrolene sodium in severely affected horses may The most common extrinsic cause of sporadic ER is
decrease muscle contractures and possibly prevent fur­ exercise that exceeds the horse’s underlying state of train­
ther activation of muscle necrosis. This can be repeated ing. Horses that are advanced too quickly in their train­
in 4–6 hours. ing, those that are only ridden sporadically while being
Severe rhabdomyolysis can lead to renal compro­ continually fed full rations, and horses performing stren­
mise due to the ischemic and the combined nephro­ uous exercise such as racing or endurance riding without
toxic effects of myoglobinuria, dehydration, and sufficient conditioning commonly develop rhabdomyol­
NSAIDs. The first priority in horses with hemoconcen­ ysis. In addition, rhabdomyolysis may be more common
tration, or myoglobinuria, is to reestablish fluid bal­ in horses exercising during an outbreak of respiratory
ance and induce diuresis. In mild cases, administration disease. Both equine herpesvirus 1 and equine influenza
of fluids via a nasogastric tube may be adequate, but virus have been implicated as causative agents. 23,26
generally fluids are better given intravenously. Balanced
polyionic electrolyte solutions are best. If severe rhab­
domyolysis is present, then isotonic saline or 2.5% dIetary ImbalanCe
dextrose in 0.45% saline may be necessary because Horses consuming a high‐grain diet appear to be
horses often have hyponatremia, hypochloremia, and more likely to develop ER than horses fed a low‐grain or
hyperkalemia. If hypocalcaemia is present, then sup­ fat‐supplemented diet. 42,43 The grain itself may not be
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plementing intravenous fluids with 100–200 mL of responsible for rhabdomyolysis; however, high starch
24% calcium borogluconate is recommended, but intake may trigger rhabdomyolysis in horses with par­
serum calcium should not exceed a low normal range. ticular myopathies such as RER and PSSM.
Affected animals are usually alkalotic, making bicar­ Electrolyte depletion in horses can occur due to
bonate therapy inappropriate. dietary deficiency and losses in sweat with strenuous