Ask A Teamster: Intramuscular Injections
by Dr. Doug Hammill D.V.M. of Montana
The article which appears below first ran in SFJ almost thirty years ago. We’ve had several readers ask about giving shots and Dr. Doug Hammill has been quite busy rebuilding after a forest fire destroyed so much of his Montana ranch, so we decided to reprint this material and give Doug a bit of a respite. SFJ
“Can you give your horse intramuscular injections?”
When I ask this question it is usually in an attempt to have the client participate in the treatment of their animal. Why do I encourage these individuals to become competent at giving injections? Our aim is top quality preventive and therapeutic care for the horse, at the least expense to the owner. Some horse persons have no desire to give their animals injections, preferring to leave that task to the professionals. Others are anxious to participate for various reasons. I think it is extremely important to recognize the distinction between giving an injection (administration), and diagnosing and/or prescribing (drug selection and dosage). I am critical of the two extremes in this respect; those veterinarians who feel they are the only ones qualified and capable of administering medication, and horsemen who independently select and use drugs without professional advice.
Administering drugs by hypodermic injection is not a procedure to be taken lightly. However, with proper instruction, some practice and a close working relationship with your veterinarian, you should be able to safely and skillfully give intramuscular injections.
We must weigh the advantages of a medication against the potential dangers, limiting injections to situations where the benefits are worth the risks. Injecting any foreign substance into the body causes some tissue damage and may result in even greater repercussions, such as inflammation or shock reactions. The best possible drug selection, dosing, handling, and administration techniques will minimize risks and maximize effectiveness.
Drugs given by injection provide the advantages of going to work rapidly, economy in some cases (less drug needed), ease and accuracy of administration, and with some products the effects last longer. Injected drugs are circulated and produce their effects throughout the body. Medication given orally may be affected by the digestive system and is often difficult to administer.
Veterinarians inject into various parts of the body for specific purposes – intravenous, intradermal, subcutaneous, intraarticular, epidural, intrathecal, intraocular, etc. We will limit our discussion here to injections into muscle tissue (intramuscular or IM injections).
My comments on drugs and vaccines will be brief. Purchase high quality products and be sure they are handled and stored properly. The decision of what products to use, and when to vaccinate or treat your horse(s) should be made by you AND your veterinarian.
Unless we use sterile (germ-free) techniques when giving IM injections, we may cause problems greater than those the injection is intended to treat or prevent. A needle should never be used on a second horse without being cleaned and sterilized after the first horse. The best method is to use a new, sterile, disposable needle for each injection. Infections or diseases such as equine infectious anemia or sleeping sickness can be transmitted from one horse to another by body fluids or blood on a needle.
If you have non-disposable type syringes and/or needles and wish to re-sterilize them, several methods are practical. Provisions must be made to maintain the sterile condition until the equipment is used. Contact with any non-sterile object or surface will result in contamination. Protection from air, with its associated germs, is important. Residual moisture or chemicals may have a harmful effect on vaccines or drugs. Needless to say, all equipment should be thoroughly cleaned before sterilization (washed and rinsed). Special attention should be paid to the inside of the needles. Dried blood, drugs, and dirt commonly cling within. It is best to replace such needles.
Boiling in water for 20 minutes is generally effective. However, it is difficult to get equipment dried and into dry sterile storage containers without contamination.
Commonly, equipment is kept in a container of alcohol. This is a reasonably effective method of sterilizing; however, some drugs and many vaccines can be damaged by alcohol. Care should be taken to see that the alcohol evaporates before equipment is used. The brief exposure to air should be no problem since alcohol evaporates rapidly. Force air through the needle with the syringe to dry the inside. Remember that disinfectant solutions do not sterilize rapidly – soaking for 15-20 minutes is necessary for most to do their job.
A pressure cooker makes an effective sterilizer (30 minutes). If protective cases are available, the syringes and needles can be sealed in them and sterilized. Well-sealed cases help maintain sterility afterwards. A syringe and needle unit (an extra needle is advisable) can be DOUBLE-wrapped in a clean cloth, a towel, or heavy paper for sterilizing. Store them in the wrappers and label with the syringe and needle size. When using the pressure cooker and other forms of heat, be careful not to melt plastic items. Wrapping the materials in a towel to prevent contact with the cooker will usually prevent melting. Dry heat – ovens, bun warmers, etc., is very apt to destroy plastic at the temperatures necessary for sterilization (170 degrees C. for 60 minutes). Again, I’ll emphasize that disposable needles and syringes offer many advantages.
The top of the drug bottle should be wiped with disinfectant before the needle is inserted to withdraw the drug. Alcohol is commonly used. A protective cap on the needle will prevent germs in the air from contaminating it before and after filling the syringe. Heat or gas sterilized needles and syringes are preferred since some drugs and vaccines are harmed by chemical disinfectants or moisture. The needle, except its hub, should touch only the stopper of the bottle and the skin of the animal (when inserted). If anything else accidentally contacts the needle, replace it with a sterile one. This also applies to the open tip of the syringes. Replacement of a contaminated needle or syringe is an insignificant expense compared to infection at an injection site. The person giving the injection should have clean hands and take special care not to touch the shaft of the needle, the interior or tip of the syringe or the top of the bottle.
A certain amount of controversy exists regarding disinfecting the skin and hair of the animal. Unless an area is clipped, scrubbed thoroughly and rubbed with alcohol or a similar disinfectant, sterility is probably not attained. Such extreme preparation for an IM injection is not justified, in my opinion. Briefly wetting or wiping the hair and skin with disinfectant may simply loosen and mobilize germs rather than destroy them. Consequently, I choose to make my injection without special treatment of the skin surface if it is reasonably clean. Don’t inject an area that is soiled by mud or manure – choose a clean site elsewhere or clip, scrub and disinfect the area.
For intramuscular injections in the horse or mule I use either an 18 gauge or 20 gauge needle, 1½ inches long. I like to inject deep into the muscle, not near the skin surface. 18 gauge needles are used for thick solutions that will not flow easily through the smaller diameter 20 gauge. I insist on a sterile needle for each and every injection. Although needles can be cleaned and re-sterilized I use and recommend the disposable type. By using them you are not only assured of sterility, but avoid problems such as dullness, loose hubs, plugged or bent needles.
Metal, glass, nylon and plastic syringes are available. For years, I have used only the plastic disposable type (as illustrated) and find no need for the others. They come sterilized and sealed in individual plastic cases. These syringes are often cleaned, sterilized and re-used although purists frown upon the procedure. Syringe size depends upon the dosage requirements. A variety of sizes are available prepackaged as individual doses loaded in a disposable syringe ready to inject. Syringes are marked off to measure volume in milliliters (ml) or cubic centimeters (cc.) or both. A milliliter and a centimeter are equal (10cc. – 10 ml. etc.).
Drug dosages are usually given in terms of ml. or cc. However, other forms of measurement sometimes complicate things. The milligram (mg.) is a measure of weight, not volume. It is not equal to nor the same as the ml. The concentration of many drugs is expressed as a given number of milligrams per ml. (or cc.). For example, a bottle on my shelf contains 50 mg. of the drug gentamicin sulfate per ml. of solution in the bottle. The usual dosage for this product can be expressed as 50 ml. (50 cc.) per mare, or as 2,500 mg. (50 mg. in each ml. X 50 ml. = 2,500 mg.) Be certain of the dosage you want to give – don’t confuse ml. and mg. Some dosages are listed as a given number of cc/pound of body weight (or ml./lb). Others may be in terms of mg./lb. International Units (IU) are sometimes used rather than ml., cc., or mg. as a measure of the amount of a drug. Some dosages are expressed as IU/lb. Your veterinarian knows about all these and can assist you if necessary.
We now see that it may be necessary to determine the weight of the animal in order to administer the dose that has been decided upon. Many individuals can estimate the weight of livestock with reasonable accuracy. For those that cannot and don’t have easy access to a scale there is an alternative. Several feed companies have weight tapes available. By measuring a horse’s girth with the tape the weight is read on a scale. These tapes are surprisingly accurate; however, I haven’t found one where the scale goes high enough for heavy draft horses. Whatever method is used, a reasonably accurate weight should be determined for calculating the dosage. Vaccines are usually dosed with a specific volume per horse regardless of size. Most other drugs are dosed according to body size. (wt).
Weight = Heart girth X Heart girth X Length, divided by 300, plus 50
Length = Measurement in inches from the point of the shoulder to the base of the tail diagonally along the curve of the body.
Heart girth = Measurement around the chest just behind the withers in inches.
Heart Girth = 87.5 inches.
Length = 77.5 inches.
87.5 X 87.5 X 77.5 = 593,359.37
593,359.37 divided by 300 = 1977.865
1977.865 + 50 = 2,027.87 pounds
This method was found to be within 3% of scale weights when tested on over a thousand horses.
Always be certain that you have your dosage correct. Underdosing and overdosing are common errors. Don’t be taken in by the misconception that a small amount should be used for a mild condition and large amounts for a severe condition.
Loading the Syringe
Figure 1 shows a 35cc syringe and 18 gauge, 1 ½” needle in their cases, along with an antibiotic solution. After twisting and removing the caps on the syringe and needle cases we can remove the syringe and slide the hub of the needle onto the syringe tip. The protective cap over the shaft of the needle should remain in place to prevent contamination. Some needles lock onto the syringe, the type illustrated does not.
AT THIS TIME, CHECK THE LABEL ON THE BOTTLE TO BE ABSOLUTELY SURE YOU HAVE THE RIGHT DRUG. Next, shake the bottle well and wipe the rubber stopper on the bottle with disinfectant. Remove the needle cap (keep it clean) and withdraw the plunger of the syringe until you have drawn enough air into the syringe to equal the volume of drug to be used. Force the needle through the rubber stopper and SLOWLY inject the air into the bottle (Fig. 2). This air will replace the volume of drug to be removed, preventing a vacuum in the bottle. If a vacuum is created it becomes difficult to remove the solution. Maintain control of the plunger so the pressure you’ve created doesn’t force the plunger back out of the syringe and onto the ground. With the bottle upside down withdraw the plunger to pull the drug into the syringe (Fig. 3). Some air may enter the syringe so I usually withdraw the plunger past the dosage mark letting the air accumulate near the upper (tip) end of the syringe. When I have overdrawn enough to account for the amount of air in the syringe, I force the plunger in until it reaches the mark for the desired dose. The air is forced back into the bottle. Sometimes it is necessary to force the air in and withdraw more solution several times to get the dose correct without air in the syringe. Contrary to what many believe, INTRAMUSCULAR injecting of air presents no serious threat to the animal’s life. Nevertheless, it should be avoided. Air in the syringe with the drug affects the accuracy of the dose. To remove air bubbles from the solution in a syringe, thump or flick the barrel of the syringe sharply with your fingernail several times. This jars the bubbles and they float up to the tip where they can be forced back into the bottle and the dosage readjusted. Once satisfied that the correct amount of drug is loaded, withdraw the needle from the bottle and recap it. The syringe is now loaded and ready for the unsuspecting victim. (Fig.4)
I have some definite opinions regarding what specific areas of the body should be used for intramuscular injections and those that should not. A good site for IM injection should contain large muscle masses and be relatively free of bone, vessels, nerves, ligaments, and glands. I want to use an area that will cause the animal the least discomfort and/or disability if post-injection complications result. Characteristically, three locations are popular – the chest, the side of the neck, and the hip (rump). The shoulder and the thigh are sometimes used.
The heavy muscle of the rump or hip region is the area I prefer to use. The area within the white rectangle on the mule’s hip in Fig. 5 is my target. Avoid the vicinity of the white X as the hip bone is close to the surface there. The backbone area on the top midline must also be avoided. Some horsemen and veterinarians have told me they don’t like this location because of the danger of being kicked while working there. I have not found this to be a problem and will comment on it later. Basically, I use the hip location most of the time because over the years I have seen fewer post-injection problems there. I also feel that occasional complications such as soreness and swelling affect the horse less seriously in the rump area than they do in the neck, shoulder, chest, or thigh. In fact, I refuse to give intramuscular injections in the neck muscles because of this. (Let me emphasize that many people prefer the neck; it is one of the generally recommended sites; and I don’t intend to offend anyone that uses or recommends it.)
The neck contains a lot of fibrous tissue and ligaments. If the injection is made into such tissues between the muscle bundles, a greater chance of inflammation or abscess exists. By placing the injection in the recommended small triangular area of the neck, chances of problems are reduced. Outside this area are structures such as the neck vertebrae, trachea (windpipe), carotid artery, jugular vein, and the big ligament in the crest area that holds the head up. Injecting into or even near these structures can have serious consequences. If a horse does get sore from an injection in the neck they are often quite miserable. It may hurt them to lower the head to graze, or at times to hold it up. Chewing, swallowing, and just moving the head to look around or fight flies may be painful. Performance is often affected. I think the overall effect on the horse is usually worse with neck pain or injury than with comparable pain in the other injection areas. Rarely, permanent scarring, tissue damage, or restriction of function occurs, and I feel the neck is the most undesirable of all the sites at which to have these.
An animal can get sore or have other complications at any of the injection sites. I haven’t seen problems in the shoulder or thigh areas but I rarely see animals that were injected there. My feeling is that if they get sore in these locations it will likely be more painful to move than with a similar problem in the hip or chest region. This probably is not as true with the thigh as the shoulder. However, many horses don’t stand well for needles in the thigh region. I often use the thigh for IM injections in young foals. Relative to the other areas the muscle mass is larger in youngsters.
The chest presents a small area for injection and swelling tends to occur somewhat more easily than in other areas. I limit my use of the chest to small volume injections such as vaccines (1-2 cc. commonly). If swelling does occur here it rarely produces much discomfort, in my experience. The soft area marked with the white square in Fig. 6 is your target. Avoid the breast bone in the middle of the chest (near the left edge of the square) and the X which marks the bony point of the shoulder. The vertical groove between the legs and the chest contains some vessels and nerves so stay over on the chest rather than in this furrow.
I try to avoid injecting where harness and friction may add to the irritation and tissue disturbance caused by the injections. The neck sites are under and just ahead of the collar. The breeching exerts pressure on the thighs, and the tugs come over the shoulder. While the quarter straps come over the hips, the friction and pressure they exert is not great and is not expected to cause problems. I try to avoid giving vaccinations prior to situations or events where appearance or performance is critical. While most injections produce no visible adverse effects, why take a chance? Don’t delay needed treatment, however.
Handling the Animal
Our discussion, so far, has been about things that can affect the physical well-being of the animal. From this point on the safety of the persons working with the animal must also be considered. While the majority of animals injected do not react in a dangerous manner, we must preplan for the unexpected. Consider the best tactics and psychology to use in order to minimize upset to the animal. This is one of the best ways to promote safety for those handling him. I work very hard to insure the animal is not conditioned to think of an injection as a bad or painful experience. Admittedly, success in this respect is variable. The procedure is one that will need to be repeated many times during the animal’s life. Try to make it as pleasant as possible. I first attempt to get the animal’s confidence. Don’t rush up and jab him – casually and calmly approach the head. I usually leave my arms down at my sides rather than reaching out. Somehow I feel many horses accept my reaching for them better if they first reach out and check me over. Next rub him a little on the face in front of the eye or on the neck. By this time you should have some impression of how well you are being accepted. If he is relaxed and unsuspicious, work your hands over the body towards the chosen site and proceed with the injection. Keep in mind that you may surprise or hurt even the calm animal, producing unexpected reaction by him.
If the horse or mule remains nervous or suspicious, I feel it pays to take more time and be patient. Above all, remain calm and relaxed; if you or the handler are frustrated, mad, nervous, or frightened, the animal will sense it and react unfavorably. Getting upset only upsets the animal, especially young animals. There comes a point when judgement tells us that some horses are not just nervous or suspicious (lacking confidence) but rather neglecting their manners and respect for us. In such cases, a firm (but calm) word or jerk on the lead rope may be enough of a reminder. If not, it sometimes becomes necessary to pinch a handful of skin on the neck or shoulder as a distraction and reminder of firmness. A twitch may be used if necessary (rarely needed). If you are unsuccessful, at this point, in getting the animal to stand so that you feel you can safely inject, consider some form of restraint. The chute in Fig. 7 is safe, easily constructed, and one of the things horsemen can’t understand why they did without once they build one. We built ours along a plank fence but both sides can be like the left. It not only keeps the animal in one place but offers some protection from kicking and striking. If a safe chute, alleyway or stall is not available a front or rear leg may be tied up in extreme cases. Other “pet” techniques are, no doubt, safe and effective.
I prefer to have someone hold the horses rather than tying them – it’s safer. They should be on the same side you are, not in front of the animal nor on the other side. Keep the head up and held short in a calm, comforting, but firm manner.
When injecting the hip area I stand near the shoulder (Fig. 8). With one hand on the neck for constant contact with the animal, I work my other hand along the back to the hip. I rub in a comforting manner as I work my way back (don’t lightly tickle). The hand I work towards the hip with is holding the needle by its hub. Care must be used to keep the needle from touching the horse or mule until inserted. Be watchful for the animal that sidesteps on your toes. Let me emphasize that you can be kicked standing where I am in the picture – it is not out of the animal’s reach by any means. But then, I never consider myself out of their reach by kicking or striking if I’m close enough to touch or inject them anywhere on the body. If careful observation indicates they may kick, take measures to prevent it and protect yourself. I find most animals that react to the needle do so by moving away from me, humping their back, hopping in the rear a few times, or half-heartedly kicking out backwards. There are rare exceptions – you had better outguess them ahead of time (regardless of where you stand or inject).
To inject the chest, I again stand beside the shoulder, but further from the animal’s side (Fig. 9). I’m in a little better position to be missed by a hind foot although probably not with a mule. Notice my hand on top of the neck to maintain constant contact while inserting the needle.
When you are satisfied the animal is ready, remove the needle from the syringe and the cap from the needle. By holding the needle as in Fig. 10, the back of the hand can be used to rub and work its way from the head or neck region to the injection site. Keep the needle clean. After rubbing the injection area a little, I pat or slap the place a couple of times – gently at first, evaluating any response by the animal, and then harder. This is done with the back or heel of the hand while holding the needle as in Fig. 11. After a couple of slaps, bring your hand down again so that the needle is driven in to the hub and the hand slaps or thumps the area much as before. If done properly and in sequence with the other slaps, the horse will expect it and feel your hand more than the needle. A common error is to hesitate and attempt to force the needle in lightly, gently and with hope of less pain. Any hesitation will result in the animal feeling it more. Slap the needle in fast and deep and rely on your hand hitting to create a diversion. Fig. 12 shows the needle in place. If your subject reacts and moves around at this stage, calm him before proceeding. If blood leaks out of the needle insert a new, sterile needle in a spot a few inches away as explained above. Steady the needle hub with one hand while attaching the syringe with the other (Fig. 13). With practice this can be done with one hand while maintaining neck contact with the other. Be sure the syringe tip is securely seated in the needle hub. Pull OUT on the plunger (aspirate) to see if blood enters the syringe (Fig. 14). If it does, insert a new, sterile needle in a spot a few inches away as explained above. We don’t want to inject into a blood vessel (into the blood stream) as some drugs cause serious problems there. Be sure to aspirate EVERY TIME before you give an IM injection. Now force the plunger inward slowly. Hold and support the syringe so it doesn’t push the needle hub into the skin too hard (Fig. 15). Withdraw the syringe and needle with a smooth, quick motion. Briefly massage the spot where the needle was removed – this keeps blood or the drug from leaking out the needle hole. At this point a little time is well-spent rewarding the horse or mule. The actual injection procedure takes but a few seconds so it’s easy to spend greater time before and afterwards doing pleasant things. Try to make the animal’s memories of the event mostly positive. The injection procedure is the same for the chest or other sites. If repeated injections are necessary, try to vary the locations to avoid too much irritation and tissue damage in one area. It is generally recommended that not over 10 cc. be injected IM in one place. I routinely give up to 10 cc. of penicillin-streptomycin preparations at one site in the hip. However, I would not inject this large a volume of some other drugs at one site. I urge you to follow specific recommendations from your veterinarian.
Complications and Problems
Problems do occasionally arise in the process of, or after IM injections. Top quality products, equipment, sterility, and technique greatly reduce the chance of problems. Some conditions I have observed that concern me are: use of dull, bent or unclean needles and/or dirty syringes; drugs being used past the expiration date printed on the bottle; dirty bottle stoppers; drugs and vaccines neglected by exposure to freezing or overheating; improper drug mixing or shaking; improper dosages; selection and use of improper or poor quality drugs and vaccines. If a needle breaks off, the portion in the animal must be removed as soon as possible. Minor inconvenience sometimes results from such problems as syringe plungers pulling out of the barrel while filling. If the syringe tip doesn’t seat tightly in the needle hub, the solution may squirt out between them when the plunger is pushed to inject. Attach the syringe well and depress the plunger slowly with moderate pressure. Blood or drug leaking out of the needle hole in the skin has been mentioned. In freezing weather the drug sometimes freezes inside the needle, plugging it. Wait a few moments after placing the needle in the horse – the body heat will thaw it out so you can inject. Keeping the syringe with a capped needle in an inside pocket as long as possible may prevent freezing. The problems of injection of air, injection into the blood stream, disease transmission and volumes too large at one site have been previously discussed.
Local tissue reaction always occurs to some degree at the injection site. Often there are no outward signs of this. Slight tenderness or very mild swellings of short duration, are not too uncommon. If the tissue is more seriously irritated or damaged, pain, swelling (hard or soft), and heat increases in the area. Some drugs are more irritating to tissue than others, and some horses more sensitive to irritation than others. If the injected material is deposited in an area with poor circulation, it cannot be moved away rapidly by the blood. The longer it remains in an area before entering the circulation, the greater chance of tissue irritation. Large volumes displace and disrupt more tissue than small doses and are not moved out by the circulation as rapidly. Inflamed areas benefit from hot packing (holding hot, water-soaked towels over the area or soaking with a hot water hose). Exercise, if not too painful, will increase circulation and may be beneficial. If pain and swelling become severe or persist for more than 2 or 3 days, consult your veterinarian. Severe inflammation can progress to abscess formation (pus filled pocket in the tissue. This is uncommon but the associated tissue destruction can be serious – permanent scarring or functional disabilities sometimes result. Infections resulting from poor sterile technique or bacteria carried in from the skin on the needle may produce similar abscess problems. Get professional assistance immediately if fluid-filled pockets, drainage, open sores or high fever develop.
It is possible for animals to have allergic reactions to injected drugs. Fortunately, this is an unusual occurrence. Such reactions vary from simple skin welts (“hives”) to serious, or rarely fatal, shock-like reactions anaphylaxis). Generally, such reactions occur within a few minutes to a few hours after injection. Raised, plaque-like skin swellings around the point of injection are an early indication of problems. Difficult and/or rapid respiration, weakness, sweating, anxiety, salivation, stalking up (swelling of the lower limbs), frequent urination, colic, or combinations thereof indicate a serious situation. I consider them as emergency symptoms when they follow an injection. We have some good drugs for treating reactions when necessary. In extreme cases animals may stagger, go down, convulse and die. Let me emphasize again that EXTREME REACTIONS AND DEATH ARE RARE. Be aware that they do exist and know how to recognize them. Don’t be frightened away from a good vaccination or treatment program by them. Many, many more horses are lost to, or suffer from, disease or illness due to lack of proper vaccination or treatment than are affected adversely by injections.
Doc Hammill lives on a ranch in Montana. He and his partner Cathy Greatorex help people learn about gentle/natural horsemanship and driving and working horses in harness – through writing, workshops, demonstrations, lectures, and his horsemanship video series. www.DocHammill.com