Effects of preemptive atropine administration on incidence of medetomidine-induced bradycardia in dogs.
OBJECTIVE
To determine the cardiorespiratory effects of preemptive atropine administration in dogs sedated with medetomidine.


METHODS
Randomized crossover trial.


METHODS
12 healthy adult dogs.


METHODS
Dogs underwent 6 treatments. Each treatment consisted of administration of atropine (0.04 mg/kg [0.018 mg/lb] of body weight, IM) or saline solution (0.9% NaCl, 1 ml, IM) and administration of medetomidine (10, 20, or 40 microg/kg [4.5, 9.1, or 18.2 microg/lb], IM) 10 minutes later. Treatments were administered in random order, with a minimum of 1 week between treatments. Cardiorespiratory effects before and after atropine and medetomidine administration were assessed. Duration of lateral recumbency and quality of sedation and recovery were assessed.


RESULTS
Bradycardia (heart rate < 60 beats/min) was seen in all dogs when saline solution was administered followed by medetomidine, and the dose of medetomidine was not associated with severity or frequency of bradycardia or second-degree heart block. However, a medetomidine dose-dependent increase in mean and diastolic blood pressures was observed, regardless of whether dogs received saline solution or atropine. Preemptive atropine administration effectively prevented bradycardia and second-degree heart block but induced pulsus alternans and hypertension. The protective effects of atropine against bradycardia lasted 50 minutes. Blood gas values were within reference limits during all treatments and were not significantly different from baseline values. Higher doses of medetomidine resulted in a longer duration of lateral recumbency.


CONCLUSIONS
Preemptive administration of atropine in dogs sedated with medetomidine effectively prevents bradycardia for 50 minutes but induces hypertension and pulsus alternans.
Ko
J C
JC
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32608, USA.
Fox
S M
SM
Mandsager
R E
RE
D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000008:administration & dosage / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced / Q000517:prevention & control / Q000662:veterinary*; D018592:Cross-Over Studies; D003490:Cyanosis / Q000662:veterinary; D004283:Dog Diseases / Q000139:chemically induced / Q000503:physiopathology / Q000517:prevention & control*; D004285:Dogs / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D016014:Linear Models; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D014059:Tongue / Q000473:pathology
D000316:Adrenergic alpha-Agonists; D018727:Muscarinic Antagonists; D001285:Atropine; D020926:Medetomidine