Comparative study between atropine and hyoscine-N-butylbromide for reversal of detomidine induced bradycardia in horses.
Authors: Pimenta E L M, Teixeira Neto F J, Sá P A, Pignaton W, Garofalo N A
Journal: Equine veterinary journal
Summary
# Editorial Summary: Anticholinergic agents for detomidine-induced bradycardia Detomidine sedation reliably produces bradycardia and reduced cardiac output, which can compromise cardiovascular stability during equine anaesthesia. This crossover study in six horses compared atropine (0.02 mg/kg) and hyoscine-N-butylbromide (0.2 mg/kg) administered ten minutes after detomidine (0.02 mg/kg), measuring heart rate, cardiac index, blood pressure, and gastrointestinal function over 24–96 hours. Both drugs effectively reversed bradycardia within five minutes (heart rates of 79 and 75 bpm respectively), but atropine's chronotropic effect persisted significantly longer, whilst hyoscine returned to intermediate values between atropine and saline controls. The critical caveat was that both anticholinergics triggered marked hypertension (mean arterial pressures exceeding 180 mmHg), though only atropine demonstrated prolonged intestinal ileus (ten hours versus four hours for hyoscine and controls) and caused colic in one horse; gastrointestinal transit times overall did not differ between treatments. For practitioners, this work suggests hyoscine offers shorter-lived cardiovascular effects than atropine without perpetuating detomidine's depressant effects on gut motility, yet the severe hypertensive response to both agents argues against their routine prophylactic use—reserving anticholinergic intervention for cases where bradycardia poses genuine clinical risk warrants serious consideration.
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Practical Takeaways
- •Hyoscine may be preferred over atropine for reversing detomidine-induced bradycardia due to shorter duration of action and less intestinal dysfunction, but routine anticholinergic use with detomidine is not recommended due to severe hypertension risk
- •If anticholinergics are necessary, monitor blood pressure closely as both agents caused marked hypertension (>180 mmHg) during treatment
- •Consider that atropine carries a colic risk and significantly delays return of normal intestinal auscultation scores (10 hours) compared to hyoscine (4 hours)
Key Findings
- •Hyoscine increased heart rate significantly within 5 minutes of administration (75 ± 8 beats/min) with shorter duration of effect compared to atropine (79 ± 5 beats/min)
- •Atropine maintained elevated heart rate significantly longer than hyoscine but caused prolonged auscultation score recovery (10 h vs 4 h)
- •Both anticholinergics caused significant hypertension (mean arterial pressures >180 mmHg) coinciding with increased cardiac index
- •Hyoscine did not impair gastrointestinal transit or intestinal motility, whereas atropine induced colic in one horse and caused delayed auscultation score recovery