Use of phenytoin to treat horses with Australian stringhalt

Aust Vet J. 1991 Jul;68(7):221-4. doi: 10.1111/j.1751-0813.1991.tb03210.x.


Five horses with Australian stringhalt were treated with 15 mg/kg phenytoin orally for 2 weeks. During the second week of the trial, 3 of the horses were given an additional dose of 10 mg/kg phenytoin. The response to treatment was clinically assessed by grading the severity of the gait abnormality at the walk, trot, turning and backing twice daily. There was a significant (P less than 0.05) improvement in the gait abnormality when pre-treatment values were compared with the mean of the last 3 assessments before treatment stopped. When reassessed 2 weeks after treatment ceased, there remained a significant (P less than 0.05) improvement compared with pre-treatment values at the trot and on backing, but not at the walk or turning. Surface electromyographic recordings were made weekly from the long digital extensor muscle, and there was a change to a near normal recording by the end of treatment. Plasma phenytoin concentrations were monitored during the trial, and the dose rates used achieved a steady state with a mean plasma level of 37 +/- 7 mumol/l. There was wide variability between plasma concentrations in different horses, although there was no difference in absorption between administration of the phenytoin as a paste, or when it was mixed in the feed. Although mild tranquilization was seen after treatment, there were no clinical, haematological or biochemical signs of toxicity from the phenytoin therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Animals
  • Electromyography / veterinary
  • Horse Diseases / drug therapy*
  • Horses
  • Muscles / physiopathology
  • Muscular Atrophy / drug therapy
  • Muscular Atrophy / veterinary*
  • Neuromuscular Diseases / drug therapy
  • Neuromuscular Diseases / veterinary*
  • Phenytoin / administration & dosage
  • Phenytoin / blood
  • Phenytoin / therapeutic use*


  • Phenytoin