An IM injection is short for intramuscular injection; it is a method of administering medication deep into muscular tissue with the use of a syringe. This method of delivery makes it easier for the medicine to be absorbed into the bloodstream. Apart from medicines, most inactivated vaccines are also administered via intramuscular injections.
Intramuscular injections are often advised in cases wherein other methods of administration will be ineffective or not recommended. Other medicine administration routes include oral, sublingual, nasal, transdermal, intravenous (IV) injection and subcutaneous injections.
Medicine administered via the IM route is generally absorbed faster than subcutaneous injections, because muscle tissues have a larger volume of blood supply. Muscle tissues can also hold a larger amount of medicine compared to subcutaneous injections. Medicines injected via the IV route is absorbed faster than the IM route. However, some medicines causes irritation to the veins, and for these medicines, IM injection is the ideal way of administering the medicine.
The ideal site of IM injections are usually the parts of the body that have ample muscle tissue, such as the deltoid (shoulder) muscle, the thigh and the buttocks. Drug uptake is normally slower when the IM injection site is on the thigh compared to the shoulders. However, thigh injections are preferred by patients who self-administer the drugs. IM injections via the buttocks is generally regarded as the safest site to inject both for children and adults.