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S-ketamine versus racemic ketamine in dogs: their relative potency as induction agents

Casoni, Daniela, Spadavecchia, Claudia, Adami, Chiara
Veterinary anaesthesia and analgesia 2015 v.42 no.3 pp. 250-259
acepromazine, analysis of variance, anesthesia, clinical trials, demographic statistics, dogs, ketamine, methadone, t-test
To determine the potency ratio between S-ketamine and racemic ketamine as inductive agents for achieving tracheal intubation in dogs.Prospective, randomized, ‘blinded’, clinical trial conducted in two consecutive phases.112 client-owned dogs (ASA I or II).All animals were premedicated with intramuscular acepromazine (0.02 mg kg−1) and methadone (0.2 mg kg−1). In phase 1, midazolam (0.2 mg kg−1) with either 3 mg kg−1 of racemic ketamine (group K) or 1.5 mg kg−1 of S-ketamine (group S) was administered IV, for induction of anaesthesia and intubation. Up to two additional doses of racemic (1.5 mg kg−1) or S-ketamine (0.75 mg kg−1) were administered if required. In phase 2, midazolam (0.2 mg kg−1) with 1 mg kg−1 of either racemic ketamine (group K) or S-ketamine (group S) was injected and followed by a continuous infusion (1 mg kg minute−1) of each respective drug. Differences between groups were statistically analyzed via t-test, Fisher exact test and ANOVA for repeated measures.Demographics and quality and duration of premedication, induction and intubation were comparable among groups. During phase 1 it was possible to achieve tracheal intubation after a single dose in more dogs in group K (n = 25) than in group S (n = 16) (p = 0.046). A dose of 3 mg kg−1 S-ketamine allowed tracheal intubation in the same number of dogs as 4.5 mg kg−1 of racemic ketamine. The estimated potency ratio was 1.5:1. During phase 2, the total dose (mean ± SD) of S-ketamine (4.02 ±1.56 mg kg−1) and racemic ketamine (4.01 ± 1.42) required for tracheal intubation was similar.Racemic and S-ketamine provide a similar quality of anaesthetic induction and intubation. S-ketamine is not twice as potent as racemic ketamine and, if infused, the potency ratio is 1:1.