What you see. The starting point for addressing any equine health related issue is your observation.


Medication or Vaccine Given, Concerned about Adverse Reaction


If you or your vet has recently given your horse a medication or vaccine, it is important to monitor the horse for an adverse reaction afterwards. While adverse reactions are rare, they do occur.

Common reactions include a procaine penicillin reaction (when accidentally injected into the vein, a serious and often violent response quickly ensues), intracarotid injection (misdirected IV injection into the carotid artery, causing an almost immediate seizure-like response with the horse falling and flailing on the ground), allergic or anaphylactic reactions (resulting in swellings, bumps, hives, itchiness, and/or difficulty breathing), and local inflammatory reactions (swelling, redness) that can occur soon after injection or hours later.

  • Code Red

    Call Your Vet Immediately, Even Outside Business Hours
    • If you have any questions about reaction to a medication given.
You also might be observing
Very Common
Less Common
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your role


What To Do

Depending on the medication given and your horse's response, this could be a veterinary emergency. Additionally, you should consider your own safety when handling a horse experiencing a severe medication-related reaction. When in doubt, call your vet immediately and discuss your findings and concerns.

What Not To Do

Do not take a wait and see approach if you feel your horse is experiencing an adverse reaction to a medication.

your vet's role

Your vet's action is determined by the specific situation. In some cases, your vet may advise a "wait and see" approach. In others, they will want to immediately examine the horse and possibly treat it preemptively.
Questions Your Vet Might Ask:
  • What medication was given?
  • What signs, exactly, are you seeing?
  • How long ago did you give the medication?
  • What medication did you give, how much, and by what route?
  • What are the results of the Whole Horse Exam (WHE)?

Treatments Your Vet May Recommend

A way to resolve the condition or diagnosis. Resolving the underlying cause or treating the signs of disease (symptomatic treatment)

Very Common
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Author: Doug Thal DVM Dipl. ABVP