Improving our understanding of pet owners' perceptions and knowledge related to anesthesia, surgery, and pain may lead to improved client education, satisfaction, and compliance with administration of analgesics.
OBJECTIVE To determine the pharmacokinetic and pharmacodynamic effects of midazolam following IV and IM administration in sheep. ANIMALS 8 healthy adult rams. PROCEDURES Sheep were administered midazolam (0.5 mg/kg) by the IV route and then by the IM route 7 days later in a crossover study. Physiologic and behavioral variables were assessed and blood samples collected for determination of plasma midazolam and 1-hydroxymidazolam (primary midazolam metabolite) concentrations immediately before (baseline) and at predetermined times for 1,440 minutes after midazolam administration. Pharmacokinetic parameters were calculated by compartmental and noncompartmental methods. RESULTS Following IV administration, midazolam was rapidly and extensively distributed and rapidly eliminated; mean ± SD apparent volume of distribution, elimination half-life, clearance, and area under the concentration-time curve were 838 ± 330 mL/kg, 0.79 ± 0.44 hours, 1,272 ± 310 mL/h/kg, and 423 ± 143 h·ng/mL, respectively. Following IM administration, midazolam was rapidly absorbed and bioavailability was high; mean ± SD maximum plasma concentration, time to maximum plasma concentration, area under the concentration-time curve, and bioavailability were 820 ± 268 ng/mL, 0.46 ± 0.26 hours, 1,396 ± 463 h·ng/mL, and 352 ± 148%, respectively. Respiratory rate was transiently decreased from baseline for 15 minutes after IV administration. Times to peak sedation and ataxia after IV administration were less than those after IM administration. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated midazolam was a suitable short-duration sedative for sheep, and IM administration may be a viable alternative when IV administration is not possible.
The pharmacokinetics of butorphanol after intravenous (IVB) and intramuscular (IMB) administration in donkeys were determined in this preliminary study. Healthy male gelded donkeys (n = 5), aged 6–12 years old, were administered 0.1 mg/kg butorphanol IV or IM in a randomized, crossover design. Blood samples were obtained at predetermined intervals for 24 h (IVB) and 48 h (IMB) after administration. Plasma butorphanol concentrations were determined by high performance liquid chromatography and pharmacokinetic parameters were calculated. Following IVB administration, mean (± SE) apparent volume of distribution, elimination half-life, total body clearance, and area under the plasma concentration time curve from time 0 to infinity (AUC0−∞) were 322 ± 50 mL/kg, 0.83 ± 0.318 h, 400 ± 114 mL/h/kg, 370 ± 131 h·ng/mL, respectively. After IMB administration, a maximum plasma drug concentration of 369 ± 190 ng/mL was reached at 0.48 ± 0.09 h. The IMB AUC0−∞ was 410 ± 60 h·ng/mL. Bioavailability of IMB was 133 ± 45%. The pharmacokinetics of butorphanol in healthy donkeys was characterized by faster elimination half-life compared to values from the equine literature.
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