Which method involves drug delivery straight into the bloodstream?

The method that involves drug delivery straight into the bloodstream is intravenous administration. This route allows for the drug to be introduced directly into the circulatory system, resulting in immediate onset of action. It is especially beneficial in situations where rapid therapeutic effects are necessary, such as in emergency medicine or when administering medications that are irritants to tissues if given through other routes.

Other routes, such as buccal, intradermal, and intramuscular, involve different mechanisms. Buccal administration involves placing a drug between the gums and the inner lining of the cheek for absorption through the oral mucosa, which does not enter the bloodstream directly. Intradermal injections are made into the dermis, the layer beneath the outer skin, leading to local effects rather than systemic circulation. Intramuscular injections administer the drug into the muscle tissue, where it is absorbed more slowly compared to intravenous delivery, as it still requires absorption into the bloodstream through the capillary networks in the muscle tissue.