Where should I give an intramuscular injection to a rat? - briefly
Inject into the lateral thigh muscle (vastus lateralis) of the hind limb, using a needle length appropriate for the animal’s size. This site provides ample muscle mass and minimal risk of damaging nerves or major vessels.
Where should I give an intramuscular injection to a rat? - in detail
The most reliable location for delivering an intramuscular dose in a laboratory rat is the large hind‑limb muscle known as the quadriceps femoris, specifically the ventral portion of the thigh. This area provides ample muscle mass, minimal risk of damaging nerves or major blood vessels, and easy access when the animal is restrained.
To locate the injection point, place the rat in a supine position or gently restrain it in a dorsal recumbency. Identify the femur by palpating the bony ridge along the ventral side of the thigh. The injection site lies approximately 5–7 mm lateral to the midline of the femur, midway between the hip joint and the knee. The needle should be inserted perpendicular to the skin, penetrating the muscle to a depth of 3–5 mm, depending on the animal’s size (adult rats typically require a 25‑27 G needle, 0.5–0.7 in length).
Key procedural details:
- Animal preparation: Use a clean restraining device; apply a brief isoflurane or CO₂ sedation if required for welfare.
- Aseptic technique: Disinfect the skin with 70 % ethanol or an appropriate antiseptic; allow it to dry before needle insertion.
- Needle selection: Choose a gauge that minimizes tissue trauma while allowing the planned volume (commonly 0.1–0.3 ml for adult rats).
- Injection angle: Insert at a right angle to avoid subcutaneous deposition; confirm entry by a slight resistance followed by a smooth plunger movement.
- Post‑injection care: Apply gentle pressure with a sterile gauze for a few seconds to reduce bleeding; monitor the rat for at least five minutes before returning it to its cage.
Alternative sites, such as the dorsal lumbar paravertebral muscles, are occasionally used for smaller volumes but carry higher risk of inadvertent nerve injury and are less consistent in muscle bulk. Consequently, the ventral thigh remains the standard choice for most experimental protocols requiring reliable intramuscular delivery.