intramuscularly

Intramuscularly is an adverb describing the administration of a substance into a muscle using the intramuscular route. This mode is used for medications, vaccines, and some analgesics to achieve relatively rapid absorption into the bloodstream compared with subcutaneous routes.

Common sites in adults include the deltoid muscle of the upper arm for small-volume injections, the ventrogluteal region, or the vastus lateralis of the thigh for larger volumes. In infants and young children, the anterolateral thigh is commonly used. Site choice depends on the drug, required volume, patient age, and local practices.

Absorption from muscle tissue depends on factors such as local blood flow, muscle mass, ambient temperature, and the drug’s formulation. Water-soluble solutions generally enter the circulation more quickly than oil-based suspensions or depot formulations, which may release the drug more slowly over time.

Advantages of intramuscular administration include relatively rapid uptake and suitability for certain formulations, including some vaccines. Potential drawbacks include injection-site pain and tissue irritation, and risks such as nerve or blood vessel injury, the formation of a hematoma in patients with bleeding disorders, or infection. Proper administration is typically performed by trained healthcare professionals under sterile conditions, with attention to anatomical landmarks and patient safety.

The term intramuscularly derives from Latin intra- meaning “within” and musculus meaning “muscle.”