title: S-ketamine versus racemic ketamine in dogs: their relative potency as induction agents.
abstract: OBJECTIVE
  To determine the potency ratio between S-ketamine and racemic ketamine as inductive agents for achieving tracheal intubation in dogs.
  
  
  METHODS
  Prospective, randomized, 'blinded', clinical trial conducted in two consecutive phases.
  
  
  METHODS
  112 client-owned dogs (ASA I or II).
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Veterinary Clinical Science, School of Veterinary Medicine, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Casoni
authors.forename: Claudia
authors.initials: C
authors.lastname: Spadavecchia
authors.forename: Chiara
authors.initials: C
authors.lastname: Adami
mesh_terms: D000818:Animals; D004285:Dogs; D005260:Female; D008297:Male; D000768:Anesthesia, General / Q000662:veterinary; D000778:Anesthetics, Dissociative / Q000737:chemistry / Q000494:pharmacology; D007649:Ketamine / Q000737:chemistry / Q000494:pharmacology; D011897:Random Allocation
chemical_list: D000778:Anesthetics, Dissociative; D007649:Ketamine
keywords: S-ketamine; anaesthesia; dogs; potency; racemic ketamine