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Caregiver placebo effect in analgesic clinical trials for cats with naturally occurring degenerative joint disease-associated pain
  1. M. E. Gruen, DVM, MVPH, PhD1,
  2. D. C. Dorman, DVM, PhD2 and
  3. B. D. X. Lascelles, BSc, BVSc, PhD1
  1. 1Comparative Pain Research Program, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, North Carolina 27607, USA
  2. 2Comparative Medicine Institute, North Carolina State University, Raleigh, North Carolina 27695, USA
  3. 3M. E. Gruen, B. D. X. Lascelles, are also at Comparative Medicine Institute, North Carolina State University, Raleigh, North Carolina 27695, USA
  4. 4D. C. Dorman is also at Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, North Carolina 27607, USA
  5. 5B. D. X. Lascelles is also at Center for Pain Research and Innovation, University of North Carolina School of Dentistry, Chapel Hill, North Carolina 27599, USA
  1. E-mail for correspondence: dxlascel{at}ncsu.edu

Abstract

A literature review identified six placebo-controlled studies of analgesics in client-owned cats with degenerative joint disease-associated pain. Five studies with 96 cats had available data. Caregiver responses on a clinical metrology instrument, Client-Specific Outcome Measure (CSOM), were compared to measured activity. Cats were categorised as ‘successes’ or ‘failures’ based on change in CSOM score and activity counts from baseline. Effect sizes based on CSOM score were calculated; factors that were associated with success/failure were analysed using logistic regression. Effect sizes ranged from 0.97 to 1.93. The caregiver placebo effect was high, with 54–74 per cent of placebo-treated cats classified as CSOM successes compared with 10–63 per cent of cats classified as successes based on objectively measured activity. 36 per cent of CSOM successes were also activity successes, while 19 per cent of CSOM failures were activity successes. No significant effects of cat age, weight, baseline activity, radiographic score, orthopaedic pain score or study type on CSOM success in the placebo groups were found. The caregiver placebo effect across these clinical trials was remarkably high, making demonstration of efficacy for an analgesic above a placebo difficult. Further work is needed to determine whether a potential placebo-by-proxy effect could benefit cats in clinical settings.

  • Placebo-by-proxy
  • Arthritis
  • Osteoarthritis
  • Dispositional optimism
  • Feline
  • Accepted February 12, 2017.

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