Attenuation of the blood pressure response to exogenous angiotensin I after oral administration of benazepril to healthy adult horses.
Authors: Afonso T, Giguère S, Rapoport G, Brown S A, Coleman A E
Journal: Equine veterinary journal
Summary
# Editorial Summary: Benazepril Dosing in Horses Benazepril, an ACE inhibitor used in equine cardiovascular management, requires clarification regarding optimal dosing; this prospective study aimed to establish the lowest dose achieving clinically meaningful blood pressure control in healthy horses. Five horses received four oral doses of benazepril (0.5, 1, 2 and 4 mg/kg) in randomised sequence with seven-day washout periods, with systolic arterial pressure responses to intravenous angiotensin I challenges measured at 2, 12 and 24 hours post-administration. Peak drug efficacy occurred at 2 hours post-dosing, with 1 mg/kg benazepril achieving 46.6% attenuation of systolic pressure response to the lowest angiotensin I dose (20 ng/kg) and achieving >90% serum ACE inhibition—substantially greater than the 0.5 mg/kg dose (19% attenuation) but not significantly different from higher doses. Despite achieving robust enzymatic ACE inhibition across doses ≥1 mg/kg, the blood pressure response remained modest, suggesting that serum ACE suppression alone may not fully account for benazepril's cardiovascular effects in horses. For practitioners considering ACE inhibitors in hypertensive or cardiac cases, 1 mg/kg represents a rational starting point for future clinical trials, though the disconnect between enzymatic inhibition and haemodynamic response warrants further investigation into tissue-level ACE activity and alternative mechanisms of action.
Read the full abstract on PubMed
Practical Takeaways
- •If considering benazepril for cardiovascular management in horses, use 1 mg/kg bodyweight as the effective therapeutic dose—higher doses do not improve blood pressure control
- •Benazepril reaches peak efficacy at 2 hours post-dosing; plan drug administration timing accordingly if acute blood pressure management is needed
- •ACE inhibition alone may not be sufficient to achieve clinically meaningful blood pressure reduction in horses with cardiovascular disease—other therapeutic approaches may be necessary
Key Findings
- •Benazepril dose of 1 mg/kg bodyweight achieved significant attenuation (46.6%) of systolic blood pressure response to angiotensin I at the lowest dose tested, with no significant additional benefit at higher doses
- •Maximum inhibition of the blood pressure response occurred at 2 hours post-administration, declining by 12 and 24 hours regardless of benazepril dose
- •Benazepril doses ≥1 mg/kg resulted in at least 90% serum ACE inhibition, but this did not translate to proportional blood pressure attenuation
- •Attenuation of systolic blood pressure response remained modest in horses despite adequate circulating ACE inhibition