IM injections are not recommended due to the mouse’s lack of muscle mass. Injection may cause discomfort and local tissue irritation.
Restrain rat by either holding rat against your body and isolating the rear leg or restrain the rat in the traditional manner and grasp the hind leg and hold securely. Disinfect injection site and insert needle into the caudal thigh muscle. You first must isolate the caudal thigh muscle to prevent injection into the ischiatic nerve. Injection into the nerve may cause discomfort and lameness. Aspirate and inject. If blood is aspirated, you must reposition the needle.
***The recommended needle size for an IM injection is 25 gauge