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Research on Pergolide Treatment for Equine PPID: Owner Compliance

The study found owners were compliant with pergolide treatment of horses 48% of the time and non-compliant 52% of the time.
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The take-home message from the authors is significant: “In the event of treatment failure, rather than simply increasing the dose prescribed, it would be prudent to investigate owner medication compliance and advise on how to overcome any barriers.”

With the advent of reliable pergolide treatment for equine pituitary pars intermedia dysfunction (PPID), more affected geriatric horses are living an improved quality of life. That said, it is sometimes difficult for equine practitioners to know how compliant an owner is in administering the recommended dose and frequency. A study at the British Royal Veterinary College compared clinical records of 110 PPID-horses treated with pergolide from 2016–2019 with commentary from clients about compliance as well as laboratory analysis of basal ACTH concentrations [Hague, N.; Durham, A.E.; Menzies-Gow, N.J. Pergolide dosing compliance and factors affecting the laboratory control of equine pituitary pars intermedia dysfunction. Vet Record Jan 2021; doi:10.1002/vetr.142].

The study found owners were compliant 48% of the time and non-compliant 52% of the time. 

Compliance was defined as the horse receiving ≥90% of the recommended dose. While only half of the horses received the recommended pergolide dose, this did not affect laboratory control of PPID based on basal ACTH. (Control is defined by a horse’s basal ACTH concentration return to a value within the seasonally adjusted reference interval.) Interestingly, 74% of horses belonging to compliant owners were controlled in contrast to 67% of horses belonging to non-compliant owners.

The important points from this study that have relevance to equine practitioners are as follows:

  • Veterinarians over-estimate horse owner compliance.
  • The least compliance occurred in horses 26 years of age or older.
  • Pergolide treatment results in a rapid response with reduction of plasma ACTH concentration within a single day. Smaller reductions continue to occur over time. The initial fast response might compensate for marginal owner compliance.
  • There is also the possibility of an incorrect diagnosis or misclassification of PPID, especially if basal ACTH concentrations of autumn blood samples are elevated yet yield negative PPID concerns in the spring even without pergolide treatment. A TRH stimulation test (in non-autumn months) could yield better accuracy in diagnosis.
  • While ≥90% of pergolide dose in this study indicates compliance, it is possible that a somewhat lesser dose still results in laboratory control of ACTH.

Improvements in compliance can be helped with several veterinarian-based strategies:

  • Verbal, visual and/or written information communicated to clients about dosing requirements and necessity.
  • Advance scheduling of regular follow-up appointments to evaluate the horse and obtain blood work to assess response to treatment.
  • Reminders sent to encourage appointment scheduling.
  • Training of the entire veterinary team and support staff to relay a consistent message to owners with regard to following recommended medication treatment protocols.

The take-home message from the authors is significant: “In the event of treatment failure, rather than simply increasing the dose prescribed, it would be prudent to investigate owner medication compliance and advise on how to overcome any barriers.” 

In addition, it is helpful to determine if a horse is actually ingesting the offered medication rather than spitting it out or pushing it aside in the bucket.

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