Severe phenylephrine-associated hemorrhage in five aged horses

Area of Science:

• Veterinary Medicine
• Equine Internal Medicine
• Pharmacology

Background:

• Phenylephrine is commonly used in horses for various conditions.
• Internal hemorrhage is a rare but serious adverse event associated with phenylephrine administration.

Observation:

• Five aged horses (≥15 years old) developed severe hemothorax, hemoabdomen, or both within minutes to hours after intravenous phenylephrine administration.
• In a retrospective review of 74 horses with nephrosplenic entrapment treated with phenylephrine, 4% developed fatal hemorrhage.

Findings:

• Four out of five horses in the case series died from hemorrhagic shock.
• The risk of phenylephrine-associated hemorrhage was 64 times higher in horses aged 15 years or older compared to younger horses.
• Hemorrhage was identified as the cause of death in 3 of 74 horses (4%) treated for nephrosplenic entrapment.

Implications:

• The risk-benefit assessment of phenylephrine is crucial, particularly in geriatric equine patients.
• Veterinarians should exercise caution when administering phenylephrine to older horses due to the increased risk of severe hemorrhage.
• This study highlights the potential for phenylephrine to induce life-threatening hemorrhage in aged horses, necessitating careful consideration of alternative treatments or vigilant monitoring.