Veterinarians often give penicillin to horses during surgery to prevent infection, but the speed of injection may influence how the horse’scardiovascular system reacts. In a study of 29 horses under general anesthesia, researchers compared two methods of giving penicillin: a fast injection over one minute and a slower one over ten minutes.
Both methods caused a drop in blood pressure, but the fast injection led to a more dramatic decrease. The slower, more diluted injection resulted in a gentler decline, suggesting it may be safer during surgery. Sudden drops in blood pressure during surgery can be risky. This study suggests that slowing down the penicillin injection and diluting it more could help keep horses safer under anesthesia. These findings highlight the importance of not just what medication is given, but how it’s administered.
Another Ontario Veterinary College (OVC) study comparing two lidocaine infusion protocols to further explore how intraoperative management affects cardiovascular stability and recovery quality is also soon to be published.
“In equine anesthesia, every decision—from drug choice to administration technique—should prioritize minimizing patient risk. Our goal is always to support the horse in all phases of anesthesia (from induction to full recovery) to achieve optimal outcomes,” said Dr. Alexander Valverde, Professor, DVM, DVSc., Diplomate ACVAA at OVC.
Research Paper:
Henderson ARP, Valverde A, Marchiori J, Tisotti T, Torrent A, Côté N, Gomez DE. Effect of rapid and slow intravenous injection of sodium penicillin on arterial blood pressure in isoflurane-anesthetized horses during surgery. Vet Anaesth Analg. 2025 Mar-Apr;52(2):200-207. doi: 10.1016/j.vaa.2025.01.001. Epub 2025 Jan 6. PMID: 39863515.
Equine Guelph supports a number of high-quality projects at the University of Guelph, by virtue of funding provided largely by the racing industry (Standardbred, Thoroughbred and Quarter horse organizations): the Horse Improvement Program from the Horsemen’s Benevolent and Protective Association and the E.P. Taylor Foundation, started by veterinarians in the Thoroughbred industry, and now maintained in trust by the University and Equine Guelph.
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Notes to Editor:
Equine Guelph is the horse owners’ and care givers’ Centre at the University of Guelph in Canada. It is a unique partnership dedicated to the health and well-being of horses, supported and overseen by equine industry groups. Equine Guelph is the epicentre for academia, industry and government – for the good of the equine industry as a whole. For further information, visit www.equineguelph.ca.
Story by: Jackie Bellamy-Zions, Equine Guelph
Photos: (images available upon request)
Photo Credit: Ontario Veterinary College
Web Link(s):
Story web link: https://thehorseportal.ca/2025/09/rate-of-penicillin-administration-affects-arterial-blood-pressure/
Other web links:
Research paper: https://pubmed.ncbi.nlm.nih.gov/39863515/
Media Contact:
Jackie Bellamy-Zions
Communications
Equine Guelph
Guelph, ON N1G 2W1
519.824.4120 ext. 54756
jbellamy@uoguelph.ca