How to give an Intramuscular Injection

Occasionally horse owners are called upon to administer injections to their horses.  It is important that owners be clear on injection techniques and risks.

Types of Injections

There are two major types of injections in horses: Intravenous (IV or in the vein) and Intramuscular (IM or in the muscle).  Intravenous injections should only be left to those very experienced with this technique, as mistakes (such as using the wrong drug or giving a drug in an artery) can be fatal.

Giving an intramuscular injection is a relatively easy skill to acquire but requires strict attention to detail.

Types of Drugs

It is extremely important to remember that some drugs must not be given IM.  Certain drugs can creates massive tissue reactions and necrosis (dying of skin and muscle) when given IM.  Only administer drugs IM after discussing the drug, dosage, and formulation with your veterinarian. 

Injection Location

The most common injection sites are the side of the neck and backside of the thigh.  The chest and triceps are much less commonly used.  Avoid administering injections in the rump infection in this area and be very difficult to resolve.  If administering multiple injections for several days, it is a good idea to alternate injection sites.  The neck and thigh have relatively thick muscle mass with few nerves or arteries.  They are also in areas with good drainage (in cases of injection site abscesses).  The diagram below illustrates these sites, with the most common sites shown in red and the less common in yellow.

Injection Technique

All injections must be given in a sterile manner that is, with sterile needles (usually 18 gauge or 20 gauge 1 or 1.5 inch), sterile syringes, and sterile medication.  Any contamination of the equipment or medication can result in an infection (and abscess) at the injection site.  Ensure that the medication is not expired or contaminated and is appropriate for IM use in your horse.  Wipe the rubber cap over the medication bottle with alcohol to remove any dust or debris.  Then draw up the needed amount of medication using the syringe and needle (dont forget to shake the bottle if the medicine is a suspension).

Clean the injection site with an alcohol wipe then insert the needle perpendicular to the skin into the muscle.  Ensure that no blood can be drawn back into the syringe by pulling the plunger slightly backwards.  If no blood appears, then inject the medication with steady pressure into the muscle.  Remove the needle and dispose of it appropriately.

Important Considerations: Safety

Remember that not all horses are tolerant of injections.  Some horses may resist violently to shots and pose a serious threat to handlers.  Always administer shots with another person holding the horse and be aware of sudden, dangerous reactions.  If there is any concern regarding a horses reaction stop and reconsider.  Giving that shot is not worth the risk of serious injury.

Injection Consequences

One of the most common complications following an injection is a site reaction this can vary from a subtle (but sore) lump on the horses neck to a large swollen knot in a horse unwilling to bend his neck or lower his head.  Fortunately, this problem is temporary, and can be resolved with hot packs, anti-inflammatory medication, and time.  Injection site abscesses are the result of infection at the injection site and require medical attention.  Once the abscess has matured (soft and ready to lance), it must be opened, drained, and then flushed daily for healing to occur.  The best way to avoid an abscess is to use strict sterile technique and only administer drugs approved for IM use in horses.