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Effects of fentanyl on intraocular pressure and pupil size in medetomidine-methadone premedicated dogs: a pilot study
  1. Maria Isabel Gomez-Martinez1,2,
  2. Oscar Varela-Lopez2,
  3. Jose Luis Fontalba-Navas3 and
  4. Antonio González-Cantalapiedra2
  1. 1Anaesthesia and Analgesia Department, University of Liverpool Small Animal Teaching Hospital, Liverpool, UK
  2. 2Rof Codina Hospital, Department of Surgical Sciences, University of Santiago de Compostela, Santiago de Compostela, Spain
  3. 3Surgery Department, Vetsia Veterinary Hospital, Madrid, Spain
  1. Correspondence to Maria Isabel Gomez-Martinez; maria_isabel_gm{at}


Background This is a pilot study to evaluate the effects of fentanyl on intraocular pressure (IOP) and pupil size (PS) in dogs premedicated with medetomidine and methadone.

Methods Sixteen dogs with a median (first quartile–third quartile) age of 3.5 (1.25–6) years and a mean (sd) weight of 18.6 (9.2) kg were included. Baseline readings of IOP and PS were recorded before all dogs were premedicated intramuscularly with medetomidine (10 µg/kg) and methadone (0.5 mg/kg). Both measurements were repeated 15 and 30 minutes later. Following this, the dogs were randomly assigned into two groups. The fentanyl group received intravenous fentanyl (10 µg/kg), while the control group received the same volume of saline solution intravenously. IOP and PS measurements were measured and recorded in both groups at one, five and ten minutes after intravenous injection. Data were analysed with one-way and two-way repeated-measures analysis of variance or their non-parametric equivalents.

Results PS was significantly decreased 15 and 30 minutes following intramuscular premedication and IOP was significantly increased in the fentanyl group at all time points following intravenous administration.

Conclusions Medetomidine, methadone and fentanyl combinations are not recommended for use in patients where an increase in IOP or decrease in PS is undesirable.

  • fentanyl
  • dogs
  • intraocular pressure
  • pupil size

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  • Contributors MIG-M: data acquisition, data management, data interpretation and preparation of manuscript. OV-L: data acquisition, data interpretation, statistical analysis and revision of manuscript. JLF-N: translation. AG-C: study design and final approval.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Ethics approval The Bioethics Committee of the University of Santiago de Compostela approved the collection of data.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request.

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