Accidental coadministration of medetomidine, vatinoxan and ketamine in a cat

Abstract

An 8-month-old, Domestic Shorthair male cat was presented for elective orchiectomy. Preanaesthetic clinical examination was unremarkable. The anaesthetic plan included intramuscular medetomidine (30 μg kg^-1) and tramadol (2 mg kg^-1) for premedication followed by intramuscular ketamine (8 mg kg^-1) for induction of general anaesthesia. The premedication mixture, presumed to be medetomidine and tramadol, was given as a single injection. Approximately 15 minutes after premedication, the cat was profoundly sedated, with a heart rate of 140 beats minute^-1. A catheter was placed in a cephalic vein. Ketamine was injected intramuscularly approximately 30 minutes after premedication in line with educational objectives. Within 2 minutes of injecting ketamine, the cat was exhibiting signs of excitement (mydriasis, head tilting, ataxia) and was no longer recumbent or cooperative, and its heart rate had increased to 280 beats minute^-1. Examination of the drug vials used revealed that a combined formulation of medetomidine and vatinoxan had been inadvertently given, instead of medetomidine alone, as intended. Midazolam (0.2 mg kg^-1) was given intravenously to counteract agitation. Surgery was postponed and the cat fully recovered (normal response to external stimuli, normal gait) approximately 1 hour after midazolam had been given. The predisposing factors contributing to this medication error were probably multifactorial: trainee involvement in anaesthesia care, similar appearance of drug vials and inadequate supervision during drug preparation. The medication error could explain the adverse events of tachycardia and excitement. Tachycardia may have been secondary to the effects of vatinoxan (offsetting bradycardia caused by the alpha-2 adrenergic receptor agonist) and ketamine (increasing heart rate), and the excitement resulting from the decreased plasma concentration of medetomidine (inadequate to counteract ketamine effects) when it is combined with vatinoxan. Given the inherent limitations of a single case observation, the ability to conclusively determine causes of the observed adverse events are limited.