Pregabalin contributes to increased recovery time from isoflurane anaesthesia for magnetic resonance imaging in horses.

Background: Pregabalin reduces excitatory neurotransmitter release and is used for anxiolysis in humans, cats, and horses. The effects of pregabalin on equine recovery following isoflurane anaesthesia are unknown.

Objectives: To determine if pre-anaesthetic oral pregabalin influences recovery time and/or quality from isoflurane anaesthesia in horses undergoing elective magnetic resonance imaging (MRI) of the appendicular skeleton.

Study design: Retrospective cohort study.

Methods: Anaesthetic and recovery data from 52 healthy horses in which pregabalin (PG) was administered and 76 control horses (CG) undergoing elective MRI from July 2023 to August 2024 were reviewed. Recordings of the recovery period were blindly scored by three reviewers. Multivariable linear regression analysis was used to identify factors that impact recovery times.

Results: PG received (median [range]) 3 (1-5) doses of 3.94 (3.56-4.28) mg/kg pregabalin. More CG required butorphanol (23/76 versus PG 4/52 p = 0.008) to achieve appropriate sedation for induction and ketamine boluses during the procedure (25/76 versus 8/52, p = 0.03). PG had longer times to stand (60 [48-71] min versus CG 53 [45-64], p = 0.02). There were no significant differences in recovery quality scores between groups. Age, pregabalin, acepromazine, xylazine, time to first movement and time to extubation were significantly associated with an increased time to stand (R² = 0.79, adjusted R² = 0.77; p < 0.001).

Main limitations: The retrospective nature, limited number of cases, and overall excellent quality of recoveries may have limited detection of differences between groups. Administration of butorphanol, xylazine, and acepromazine at the discretion of an unblinded anaesthetist may have influenced the time to stand.

Conclusions: Pregabalin contributed to increased recovery times when administered to a group of healthy horses. Recovery quality scores were excellent overall, and there was no difference between groups.