title: The efficacy of dantrolene sodium in controlling exertional rhabdomyolysis in the Thoroughbred racehorse.
abstract: BACKGROUND
  Dantrolene sodium (Dantrium) has been used extensively for the treatment of myopathies in man and anecdotal evidence suggests it is of clinical benefit in the control of exercise-induced rhabdomyolysis (ER) in racehorses, although data to support this are currently lacking.
  
  
  OBJECTIVE
  To investigate the efficacy of oral dantrolene sodium in controlling ER in a randomised, double-blind, placebo-controlled crossover trial involving 77 Thoroughbred racehorses in Newmarket, UK.
  
  
  METHODS
  Horses were treated on 2 occasions 1 week apart, with treatment days coinciding with a return to exercise following 2 days box rest on each occasion. For the first treatment, each horse was randomly selected to receive either 800 mg dantrolene sodium or a colour-matched placebo administered orally 1 h before exercise. This was followed by crossover to the other treatment on the second occasion, with each horse thereby acting as its own control. Degree of ER was assessed using rising serum creatine kinase (CK) levels, by subtracting pre-exercise blood CK levels from those measured in 6 h post exercise blood samples. For each horse, the difference in change between pre- and post exercise CK values between placebo and dantrolene treatments was calculated, with positive values indicating a greater rise with placebo than with dantrolene sodium treatment.
  
  
  RESULTS
  The overall mean difference for all horses was +104.8 iu/l and the null hypothesis, that there was no true difference in non-normally distributed post exercise rises in CK values between placebo and dantrolene treatments, was rejected (P = 0.0013) using the nonparametric Wilcoxon signed rank test. Additionally, no horses given dantrolene sodium showed clinical signs of ER, whereas 3 horses given the placebo developed ER following exercise. The incidence of ER in the study was 4% (3/77).
  
  
  CONCLUSIONS
  The results confirmed that oral administration of dantrolene sodium, 1 h before exercise, had a statistically significant effect on reducing the difference between pre- and post exercise plasma CK levels compared with a placebo in the same animals, and preventing clinical ER in susceptible individuals.
  
  
  CONCLUSIONS
  This study suggested that dantrolene sodium is of use in controlling ER in the Thoroughbred racehorse. Further investigation into pre- and post exercise myoplasmic calcium levels and the repeat of the study late in the season when horses receive a much higher energy ration and more strenuous exercise would appear to be warranted.
authors.affiliation: Rossdale and Partners, Beaufort Cottage Stables, High Street, Newmarket, Suffolk CB8 8JS, UK.
authors.forename: J G T
authors.initials: JG
authors.lastname: Edwards
authors.forename: J R
authors.initials: JR
authors.lastname: Newtont
authors.forename: P H L
authors.initials: PH
authors.lastname: Ramzan
authors.forename: R C
authors.initials: RC
authors.lastname: Pilsworth
authors.forename: M C
authors.initials: MC
authors.lastname: Shepherd
mesh_terms: D000284:Administration, Oral; D000818:Animals; D003402:Creatine Kinase / Q000097:blood; D018592:Cross-Over Studies; D003620:Dantrolene / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D006734:Horse Diseases / Q000097:blood / Q000201:enzymology / Q000517:prevention & control*; D006736:Horses; D008297:Male; D009125:Muscle Relaxants, Central / Q000008:administration & dosage*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012206:Rhabdomyolysis / Q000097:blood / Q000201:enzymology / Q000517:prevention & control / Q000662:veterinary*; D018709:Statistics, Nonparametric; D016896:Treatment Outcome
chemical_list: D009125:Muscle Relaxants, Central; D003402:Creatine Kinase; D003620:Dantrolene