intramuscular

Intramuscular (IM) injection is a route of administering medications into a muscle, allowing rapid entry into the systemic circulation through the vascularized tissue. Compared with subcutaneous injections, IM administration generally achieves faster absorption and can accommodate larger volumes and certain formulations such as oil-based suspensions and vaccines.

Common IM injection sites include the deltoid muscle of the upper arm, the ventrogluteal area over the greater trochanter of the hip, and the vastus lateralis muscle on the outer thigh. The deltoid is often used for small-volume injections (such as vaccines) in adults, while the ventrogluteal and vastus lateralis sites are preferred for larger volumes or when the deltoid is unsuitable. In infants and young children, the vastus lateralis is commonly recommended. The dorsogluteal site has fallen out of favor in many guidelines due to proximity to nerves and arteries.

Formulations administered intramuscularly include vaccines, antibiotics, hormones, analgesics, and long-acting depot preparations. Absorption and onset depend on the medication’s formulation, blood flow at the site, and the volume injected; depot preparations release drug over prolonged periods.

Safety considerations include avoiding injection into an area with infection or injury, using sterile technique, and monitoring for adverse reactions such as pain, redness, swelling, or more serious nerve or tissue injury. Contraindications include patient intolerance and certain bleeding disorders; in patients with coagulopathy, IM injections carry bleeding risk. Proper site selection and technique require professional training.