Evaluating the extent to which ataxia and responsiveness to stimuli reflect the efficacy of xylazine sedation using pharmacokinetics

Background

Clinical assessments of equine sedation typically rely on subjective observations, the accuracy of which is paramount to the safety of equine veterinary procedures.

Methods

To assess the degree in which subjective clinical sedative evaluations reflect pharmacokinetic measurements of equine drug metabolism, xylazine hydrochloride, an alpha-2 adrenoreceptor agonist, was administered to 36 horses of varying breed and age at a dosage of 0.5 mg/kg body weight. Subjective clinical parameters were scored at 5-, 15-, 30-, 45- and 60-minutes post xylazine administration and included responsiveness to sound, touch, visual stimuli, and observed degree of ataxia. Blood samples were collected at each time interval and liquid chromatography tandem mass spectrometry was performed to determine serum plasma concentrations of xylazine (XC) and 4-OH-xylazine (OHXC). Spearman’s and Kendall’s rank correlations assessed associations between subjective and objective measures of xylazine sedation.

Results

Ataxia demonstrated the strongest association, showing moderate positive correlation with both XC and OHXC (r = 0.63 and r = 0.58 respectively). Whilst all individual stimuli measures were significantly (p < 0.05) associated with both XC and OHXC, correlation for each was classified as negligible, ranging from r = -0.158 to -0.247. Combined stimuli responsiveness scores marginally improved the correlation with both XC and OHXC over that of individual stimuli measures yet remained classified as negligible correlation (XC r = -0.29, OHXC r = -0.28).

Conclusions

This study highlights the limited correlation between stimuli-based sedation assessments and xylazine plasma concentrations, underscoring the importance of multifactorial evaluations with the inclusion of ataxia when assessing sedation for clinical procedures.