INTRAMUSCULAR

INJECTIONS



Supplied by Equine Veterinarians Australia (EVA)

Author: Dr Christine Smith DVM DipACVS

Learn how to give an intramuscular
injection both safely and effectively
using a comprehensive
step-by-step approach.

There are times, in the course of horse ownership, where administering an intramuscular injection becomes necessary - mainly in situations that involve treatment being given several times a day and for an extended period.

Obviously, it is neither cost-effective nor practical in most situations to have a veterinarian call past on a twice-daily basis solely for the purpose of giving this type of injection so, for many people, it’s a case of taking a deep breath and being brave enough to assume responsibility. It can still be a little daunting the first few times a collection of syringes, needles and bottles are presented by the prescribing veterinarian! Even if instructions are given at the time, the intramuscular injection process can be quite nervewracking for many horse owners - with even the more experienced admitting that it can be trickier than it looks to choose the right spot, put the needle in and ensure that the contents of the syringe actually end up where it is supposed to.

The ability to deliver an intramuscular injection certainly isn’t an essential criteria for horse ownership and, given that confidence is a key factor in it being done successfully, there may be occasions when seeking assistance from a veterinarian or experienced friend is a more sensible solution. But for those who are able to become proficient at this task, especially in locations where direct veterinary assistance is not readily accessible, it is definitely a very useful skill to have.

The neck is one of the most common sites used for intramuscular injections, partly due to the fact that the person administering the injection can do so in relative safety, out of the kicking range of the hind legs. Inserting a needle into this area, however, must be done with care as, although it seems like a straightforward procedure, there are a number of very important structures in the neck that must be avoided. These include the cervical spinal cord, which lies in the middle of the neck and is encased by the spinal vertebrae, and the nuchal ligament, which forms the topline of the neck.

To locate the target area for giving an injection into the neck, imagine that there are three borders forming a triangle when viewing the horse from the side. The top border of the triangle corresponds to the nuchal ligament, the front border to the position of the cervical spinal cord/vertebrae and the remaining border to the muscles in front of the shoulder (see diagram). Anywhere within this triangular shape is a safe site for the needle to enter although, for maximum absorption of the medication being used, it is best to aim as close as possible to the middle of the target area.
One of the most common mistakes made when giving an injection into the neck is inserting the needle too low, so it is too close to the spinal vertebrae (the front border of the triangle), which can result in damage and inflammation around the vertebral column and the associated nerves and blood vessels. On the other hand, if the needle is placed too high on the neck - that is, too close to the top border of the triangle - the medication being injected won’t be absorbed as effectively due to this area having a poor blood supply. Also, as there is relatively little muscle mass in the shoulder region and the scapula (shoulder blade) is relatively close to the surface, it is important to stay well in front of the rear border of the triangular area.

Another point to keep in mind is that the neck is a relatively small muscle mass as compared to other potential injection sites, so it can become quite sore with repeated injections - especially if the volume being administered each time is greater than 10 ml. To minimise this effect, either alternate which side of the neck is injected or consider using different parts of the horse’s body in rotation.

OPTIONAL SITES
Other acceptable intramuscular injection sites include the gluteal (rump) muscles, the hamstrings (semi-membranosis and semi-tendinosis muscles) in the hind legs and the pectoral (chest) muscles (see lead-in page for diagrams). All three of these muscle groups, however, present more of a challenge in terms of the injector’s safety and require the presence of another person to hold the horse’s head. To inject into the rump, it’s safest to stand in front of the horse’s hip and face backwards to insert the needle while, to deliver a needle into the chest, stand slightly to the side rather than directly in front. The person holding the horse should always stand on the same side as the person injecting.

SETTING THE SCENE
Having identified the most appropriate site for delivery of the injection, it then pays to devote some thought to ensuring that the environment in which the procedure will be carried out is as conducive as possible to the horse remaining under control and relaxed. A wall or corner of a stable to position the horse against can sometimes be useful in keeping it still, while a nose twitch is a handy item to have close by in case it is needed.

The assistance of a confident person to handle the horse’s head is invaluable as, in addition to providing reassurance and control, they can be called upon to try strategies such as covering the eye on the same side as the injection is to be performed with a cupped hand - should this be required. They shouldn’t, however, be expected to carry out control measures such as picking up a front leg as well as holding the head. If this is thought to be necessary, having a further person to assist is a better option, although they could find themselves in a dangerous situation should the horse rear or pull back.

Distraction can sometimes be provided by feeding grain or treats while an injection is taking place, but this method can have its pitfalls as, if the horse continues to behave in an undesirable way despite being fed, this may actually be rewarding an unco-operative attitude. A more successful form of distraction that doesn’t involve food can be to grasp a fold of skin just beside where an injection is to be given into the neck or, in the case of the rump area, to rub a fist firmly over the area to be injected. This seems to have a desensitising effect on some horses.

Finally, it’s important to realise that the behaviour of the person administering the injection often has a significant influence on the horse’s reaction - with any nervousness and tension on the part of the injector likely to translate into ‘jumpy’ and unpredictable behaviour in the patient.

NEEDLE KNOW-HOW
Predominantly to reduce the risk of contamination, a brand new needle and syringe must be used for every injection and neither the needle nor the inside of the syringe should be touched with the fingers. Following these guidelines helps to decrease the risk of infection and/or the formation of an abscess at the injection site, as may swabbing the area with a cotton ball soaked in isopropyl alcohol, which is available from chemists.

The needle used needs to be the correct size - definitely no shorter than 2.5cm (1 inch) and preferably about 4cm (1.5 inches) in length. Needle types also differ depending on the amount of solution being dispensed and its consistency, with eighteen gauge needles recommended for large volumes or viscous (thick) solutions. This needle size is identified by a pink colouring on the hub, which is the plastic piece at the top that fits over the end of the syringe. For smaller volumes of thinner medications, 20 gauge (yellow hub) or 21 gauge (green hub) needles are acceptable. The vet who prescribed the drug to be injected should also supply the appropriate size of needle and the number required, along with the correct amount of syringes.

Needles and syringes must be safely stored out of reach, especially from children and pets. A proper medical waste ‘sharps’ container (available from veterinarians) or an empty plastic container with a secure lid are both appropriate for storing used needles and, when full, disposal of either can be made through a veterinarian.

OH NO!
Thank goodness it is a rare event, but there have been occasions where horse owners have accidentally injected themselves with a drug meant for equine use only, or squirted it into their mouth or eyes. If this does happen, it’s imperative to seek medical advice promptly, remembering to take along the bottle of medication so the substance in question can be identified. Even small volumes of some equine drugs can cause a dangerously low heart rate and blood pressure, disorientation, and possibly respiratory arrest, so it is far better to be safe than sorry.

The same applies to situations where a horse owner realises they may have inadvertently made a mistake in injecting either the wrong drug or the wrong volume, in that prompt consultation with a medical expert - in this case, a veterinarian - is paramount.

PRACTICE MAKES PERFECT
The thought of ‘practicing’ the skill of inserting a needle into a live patient can be a little daunting so, for those who feel unsure of their ability to carry out this task, a sensible precaution is to try it on something that won’t move or object to a few fumbles or false starts. An orange is ideal for this, as its thick peel provides a resistence not unlike the surface of a horse’s skin, so it is possible to experience just how much pressure is required for a needle insertion to be successful. It’s also a good idea to practice attaching the syringe and injecting some fluid into the orange, just so the whole process is clear and familiar before tackling ‘the real thing’.

COMPLICATIONS AND ADVERSE REACTIONS
Although the majority of intramuscular injections, whether administered by the horse owner themselves or by a veterinarian, are undertaken without complications, there are some adverse reactions to watch out for and precautions to take to prevent them from occurring;

Dependent Oedema:
It is not uncommon for what is known in scientific terms as dependent oedema to form following an injection into a horse’s chest muscles. A mild, cool swelling that follows gravity, dependent oedema usually resolves by itself over time. If, however, the swollen area feels warm or the horse seems ‘dull’, develops a fever or appears to be experiencing pain in the region, veterinary advice should be sought. The same applies if swelling, pain or heat develops suddenly in a location that had previously been an injection site.

Abscesses and Bacterial Infections:
Certain substances that are marketed for intramuscular use have been associated with injection site reactions, including abscesses, with one of the more common of these products being flunixin meglumine (Finadyne®). One of the most serious side effects of an intramuscular injection of this drug can be a bacterial infection involving Clostridium spp. This is a severe, life threatening infection that can destroy large areas of tissue, causing a horse to become critically ill. This type of complication is very rare, but the development of local swelling, heat and pain, an elevated temperature or general ‘unwellness’ following the use of Finadyne® intramuscularly is usually an indication for intensive veterinary care.

Procaine Reaction:
One of the most common antibiotics used to treat horses, as an intramuscular injection, is procaine penicillin. The procaine constituent of this antibiotic acts like a carrier, delivering the antibiotic into tissues in order for the drug to be effective but, even if a small amount of it gains access to the blood circulation, a ‘procaine reaction’ can occur. This very frightening event can vary from muscle twitches and anxiety to violent and unprovoked kicking, pawing, seizure-like activity, lying down and even sudden death. This event is not actually an allergic reaction in most horses; it is most often caused by the procaine gaining access to the circulatory system and, subsequently, causing intense constriction of the blood vessels in the brain.

There is nothing anyone can do to help a horse once a procaine reaction has occurred, apart from keeping a safe distance away and remaining calm and quiet. There are, however, steps that must be taken to minimise the chance of such a reaction happening in the first place. These include always inserting the needle by itself first, inspecting the hub for any sign of blood then, after hooking the syringe to the needle, drawing back and again, watching the needle hub and syringe very carefully for blood traces. If blood is obtained, the needle must be removed from the horse, a new needle obtained and the injection site changed.

Unfortunately, even if no blood is detected in the needle or syringe, a procaine reaction can occasionally still occur. It is also important to keep procaine penicillin refrigerated, because if the medication reaches temperatures above 50°C, there is an increased risk of reaction.

STEP-BY-STEP Intramuscular Injection

	Preparation: 1: If the medication is in a multi-dose bottle, swab the top of this with isopropyl alcohol (or metholated spirits) before unwrapping the needle and placing it on the syringe.
	Drawing The Dose: Open the syringe pack without touching the syringe then attach the needle. Inject the air into the bottle - either into the liquid or the air space above it (4), depending on how much medication is left - then withdraw the required volume of drug.
	Remove the plastic cap on the needle with a pulling (not twisting) action, then draw some air into syringe (about the same amount as the drug to be dispensed) by pulling the plunger towards you.
	Inject the air into the bottle - either into the liquid or the air space above it, depending on how much medication is left.
	Tthen withdraw the required volume of drug.
Dispersing Air Bubbles: Turn the syringe upwards so the needle is now directed towards the ceiling and tap the side of the syringe with your finger - this being necessary to encourage any air bubbles to come to the top. Remove any extra air or bubbles by carefully depressing the plunger, then replace the bottle cap.

	Inserting The Needle: Remove the needle from the full syringe and prepare to insert it into the chosen site by approaching the horse confidently. Wipe the site with isopropyl alcohol (or methylated spirits). Unless the needle and syringe are unable to be separated (as with many single dose vaccines), it is recommended that the needle be placed into the horse first then the syringe attached. The reason for this is the weight of the syringe will often pull the needle out if the horse moves away quickly, whereas if only the needle is inserted, there is a good chance it will remain in situ. Then, as the horse calms down, the syringe can be re-connected. Additionally, if the horse jumps away and the detached needle falls to the ground, it can be replaced without fear that the syringe and its contents may have been contaminated.
	Holding the plastic hub in your fingertips, push the needle in firmly and quickly in a single motion.
	If part of the needle remains exposed, tap the hub firmly once or ‘flick’ it with your index finger so it goes in all the way.
	Delivering The Dose: Once the needle is in place, securely attach the syringe using a twisting motion then draw back a short distance with the plunger.
	After checking no blood is visible, depress the plunger in a continual motion using firm, steady pressure.
	Some resistance should be felt, but if it is really difficult to depress the plunger, try injecting more slowly. Wipe the site as needle is removed. After delivering the injection, check the size of your needle as, if it is too small, this could be what is offering the extra resistance.
	Removing The Needle: Using a twisting motion, remove the needle, place the cap back on carefully and place in a storage container for disposal .

Special thanks to Armadale Byford Veterinary clinic for thier assistance with these photographs.

Supplied by Equine Veterinarians Australia (EVA).
For information on Equine Veterinarians Australia go to the web site: www.eva.org.au

Author:
Dr Christine Smith DVM DipACVS

Christine has owned and ridden horses from a young age, and was an avid participant in pony club, show jumping and 3-Day Eventing. In 1995 Christine graduated from the Ontario Veterinary College in Canada. After completing a Large Animal Internship at Texas A&M University, Christine completed a three year residency program in Equine Surgery and Lameness at the University of California, Davis. Following completion of the residency program Christine remained at UC Davis as a staff surgeon until she relocated to Australia. In 2003 Christine joined the University Veterinary Centre Camden (University of Sydney) and is the Head of Equine Surgery. Christine is a Diplomate of the American College of Veterinary Surgeons and a Registered Specialist in Equine Surgery in New South Wales. Special professional interests include lameness, poor performance in sport and racehorses, and surgical management of colic.