Greyhound dogs have been recognized for their unique responses to some injectable anesthetics. This study compared the pharmacokinetic and anesthetic characteristics of ketamine HCl in Greyhound (G) and non-Greyhound (NG) dogs. Four male and 2 female young adult G weighing 27.4 ± 2.0 kg and 4 female and 2 male young adult NG weighing 25.6 ± 1.9 kg were studied. After baseline measurements were recorded ketamine (5 mg/kg) and diazepam (0.25 mg/kg) were administered intravenously. The dogs were intubated and allowed to breathe room air. Plasma ketamine concentrations determined by gas chromatography/mass spectrometry were measured at 2, 5, 10, 15, 20, 30, 45, 60, 90 and 120 minutes. Times from induction to extubation, head lift, sternal recumbency and standing were recorded. Two-way ANOVA and t-Test were used to analyze the data which are expressed as mean ± SE. Significant differences (P < 0.05) were separated using Fisher's Least Significant Differences. The elimination rate constant and its associated half-life were calculated by regression of the terminal 4 time-concentration data points. A model independent method of analysis was used to calculate other pharmacokinetic data. Elimination half-life (t1/2ß) was significantly shorter (31.55 ± 18.81 vs 59.04 ± 22.49 minutes) in Greyhounds. Total body clearance, although greater in Greyhounds, was not significantly different. There were no significant differences in any other pharmacokinetic parameter. Mean ketamine plasma concentrations were lower in the G group but significantly lower only at 10 minutes (1.06 g/ml vs 1.57 g/ml; standard error ± 0.17 based upon pooled estimates of variation). No significant differences were found between the groups for any of the recovery times. With the exception of t1/2ß, G dogs respond pharmacologically and clinically similar to NG dogs after ketamine-diazepam bolus administration. These results are in contrast to previous comparison studies of propofol and thiobarbiturates in G and NG dogs.
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