What is the primary characteristic of the intravenous route?

The primary characteristic of the intravenous route is that it involves injecting a solution directly into the vein. This method allows for rapid absorption and immediate effects, making it a preferred route for medications that require quick onset of action or for delivering fluids and electrolytes. Intravenous administration is particularly useful in medical emergencies or situations where patients are unable to take medications orally.

In contrast, other routes mentioned involve different methods of administration. Delivering medication through the skin refers to topical applications and transdermal patches. Placing a drug in the mouth pertains to the oral route, which involves swallowing medications that must be absorbed through the gastrointestinal tract. Finally, injecting into muscle tissue describes the intramuscular route, which has a slower absorption rate than intravenous administration. Understanding these differences clarifies why injecting a solution into the vein is the defining feature of the intravenous route.