Introduction
FIn exotic companion mammals, intramuscular (IM) injections are primarily given in the large muscles of the rear limbs or the epaxial muscles.5 Additional injection sites include gluteal muscles in prairie dogs and the biceps or triceps in sugar gliders (Petaurus breviceps) and ferrets (Mustela putorius furo).1,9
Epaxial muscles
Video produced by Katie Lennox-Phillibeck; technique demonstrated by Dr. Angela Lennox. Narration added post-production by Dr. Christal Pollock.
The epaxial muscles lie dorsal to the transverse processes of the vertebrae (Fig 1). The rabbit’s relatively large epaxial muscle mass is a popular site for IM injection and epaxial injections are generally very well tolerated in rabbits. The conscious rabbit can be maintained in sternal recumbency and drug delivery appears to be a relatively low stress technique when compared to IM injections into the thigh muscles. Epaxial injections can also be used in guinea pigs, chinchillas, prairie dogs, and other rodents.8 In the sugar glider, intramuscular injections can be given in the epaxial muscles over the neck and thorax.1,7,10
Figure 1. A transverse section illustrating epaxial and hypaxial muscular regions. Source: Herne MC, Tait AM, Weisbecker V, Hall M, et al. A new small-bodied ornithopod (Dinosauria, Ornithischia) from a deep, high-energy Early Cretaceous river of the Australian–Antarctic rift system. PeerJ 5:e4113, 2018 via Wikimedia Commons. Click image to enlarge.
Potential complication
A potential complication of any IM injection is the development of an abscess at the site of injection, however it is particularly difficult to treat this problem in such a dorsal location.12
Step-by-step technique
To perform an IM injection into the epaxial muscles…
- Select a small-gauge needle: 25-27 gauge in the rabbit; 27-30 gauge in smaller mammals.
- Restrain the patient: For larger patients, like the rabbit or guinea pig, an assistant restrains the patient either in the “football” hold or on a flat surface in sternal recumbency with one hand against the rump and another placed on the sternum to prevent movement (Fig 2).12
- Identify anatomic landmarks. Palpate the dorsal spinous processes of the vertebral column, the last rib, and the wing of the ileum. In most species, the largest epaxial muscle groups are found just cranial to the pelvis and lateral to either side of the spine (Fig 3).
- Introduce the needle perpendicular to the muscle mass (Fig 4). As with any IM injection, aspirate back on the syringe plunger to confirm a small vessel has not been accidentally cannulated. The presence of any blood indicates improper needle placement, and the needle must be repositioned.
- Only inject a relatively small amount of medication into one site to prevent the pain of muscle fiber separation (see Table 1 below).12 Divide the volume to be delivered as needed.
Figure 2. For intramuscular injection into the epaxial muscles, an assistant places one hand against the rump and the other hand on the sternum to prevent patient movement. Photo credit: Jody Nugent-Deal, RVT, VTS.
Figure 3. Identify anatomic landmarks to confirm the location of the epaxial musculature. Image taken from a video produced by Katie Lennox-Phillibeck; technique performed by Dr. Angela Lennox. Click image to enlarge.
Figure 4. Introduce the needle perpendicular to the epaxial muscle mass. Image taken from a video produced by Katie Lennox-Phillibeck; technique performed by Dr. Angela Lennox. Click image to enlarge.
Thigh muscles
Depending upon your species of interest, IM injections can be made into the quadriceps muscle group cranial to the femur or the semitendinosus/semimembranosus muscles on the caudal thigh (Fig 5).
- The thigh muscles are a popular site for IM injections in guinea pigs, chinchillas, prairie dogs, and ferrets.8,9Thigh muscles can also be used in rabbits, however, this injection site appears to be more stressful in the conscious rabbit when compared to epaxial musculature.
- The very small muscle mass in tiny patients, like the mouse or sugar glider, can make IM administration both technically difficult and painful due to distension of the muscle.6,10 Therefore IM injections are typically performed in these patients under general anesthesia and then only when absolutely necessary (see Potential complications below).6,10
Figure 5. The rabbit’s pronounced leg muscles are capable of powerful kicks; when injections are made into this muscle group more zealous manual restraint is required. Photo credit: Eva K via Wikimedia Commons. Click image to enlarge.
Potential complications
The sciatic nerve courses through the sciatic notch on the caudal surface of the femur.6 If the sciatic nerve is damaged by a poorly placed needle or irritated by certain drugs, like ketamine, this can result in lameness and self-mutilation.6,11To minimize this risk, either insert the needle at a relatively shallow angle (away from the femur) or inject the quadriceps muscle group on the cranial surface of the leg.
A relatively lightweight skeleton paired with pronounced muscles of the thighs and epaxials predisposes the rabbit to luxation or fracture of the lumbar spine or rear limb if the animal struggles.14 Therefore, more intensive manual restraint is necessary during an IM injection into the thigh muscles to prevent powerful kicks and subsequent injury.
Step-by-step technique
An IM injection into the thigh muscles is a one or two-person procedure. If the patient is conscious and liable to struggle, one person is needed to restrain the animal, and a second person is needed to administer the injection.
- Select a short, small (25-30 gauge) needle.
- Provide chemical or appropriate manual restraint. For a quadriceps injection with the rabbit sitting on a table, the handler uses their forearm to hold the rabbit snugly against their body. The rabbit’s head is tucked in the crook of the arm and the hand holds the rear leg to be injected.14
- The person administering the injection secures the rear foot nearest them, then palpates and isolates the muscle mass to be injected.
- Insert the needle at a 90-degree angle, perpendicular to the thigh. To reduce this risk of sciatic nerve damage, direct the needle away from the femur when administering an IM injection into the caudal thigh muscles. Alternatively, use the cranial quadriceps muscle group.5,11
- Aspirate to confirm a small vessel has not accidentally been punctured.
- Muscle mass in the rat or guinea pig is usually sufficient for accurate administration of small volumes of material. In smaller rodents, like the mouse, injection volumes should ideally be 0.05 ml or less. (Table 1). Split larger volumes.
- Administer the injection at a slow, steady pace.
- Withdraw the needle and observe the injection site for any bleeding. Control any bleeding by applying pressure with a finger tip or cotton-tipped applicator for at least 30-60 seconds.
Visit the Procedures With Care website to view “Intramuscular Injection in the Rat13
| Table 1. Maximum volume recommended for intramuscular injection2,3,4,6,14 | |
|---|---|
| Species | Maximum volume (ml) |
| Mouse | 0.025-0.05 |
| Gerbil | 0.1 |
| Hamster | 0.1 |
| Rat | 0.1-0.3 |
| Chinchilla | 0.3 |
| Guinea pig | 0.3-0.5 |
| Rabbit | 0.5-1.0* |
| *Note: These recommended volumes are based on large, laboratory rabbits. A volume of 0.05 ml/kg has also been described.14 | |