Which of the following routes is known for being rapid due to direct access to circulation?

The intravenous route is known for providing rapid access to the bloodstream, which allows for immediate therapeutic effects. When a medication is administered intravenously, it directly enters the circulation, bypassing any barriers that other routes may encounter, such as absorption through the gastrointestinal tract or diffusion through tissues. This direct access is particularly beneficial in emergencies or situations where rapid onset of action is crucial.

In comparison, intradermal injections involve administering medication into the dermal layer of the skin, which is slower to absorb compared to intravenous administration. Intramuscular injections do allow for relatively quick absorption, but they still take longer than intravenous delivery as the medication must diffuse into the bloodstream from the muscle tissue. The buccal route involves placing a drug between the gums and the inner lining of the cheek, which allows for absorption through the mucous membranes, but this process is also slower than that of intravenous administration.

Thus, the intravenous route is distinctively known for its speed in delivering medications directly into circulation.