This study was conducted with the objective of determining the plasma and cerebrospinal fluid (CSF) concentrations after epidurally administered alfentanil, butorphanol, and morphine in horses. Five clinically healthy adult horses were studied. Morphine 0.1mg kg-1, alfentanil 0.02mg kg-1, and butorphanol 0.08mg kg-1 in equal volumes (20ml) were epidurally injected. A 10-ml sample of CSF and blood were drawn at sampling times before the epidural administration and at 5, 10, 20, 30, 40, 50, 60 and 120 minutes, and hourly for 24 hours Enzyme-linked immonosorbent assay (ELISA) was used as the screening test to detect the injected opioids. ANOVA and Bonferroni’s test were used with a P values <0.05 considered significant. The ELISA method was used and seemed to be efficient to detect plasma and CSF epidurally administered alfentanil, butorphanol, and morphine in horses. Epidurally administered alfentanil produces fast cerebrospinal fluid levels that are higher than plasma levels. Less lipid soluble drugs such as morphine and butorphanol produce higher plasma levels than CSF levels for the same time point.
analgesia; opioids; pharmacokinetics; equine; epidural
