Which parenteral route requires the medication to be injected into muscle tissue?

The parenteral route that requires the medication to be injected into muscle tissue is the intramuscular route. This method involves administering medication directly into a muscle, where it can be absorbed quickly into the bloodstream due to the high vascularity of the muscle tissue. Intramuscular injections are commonly used for vaccines, hormones, and certain medications that require rapid absorption or larger volumes than what is typically feasible through other routes.

In contrast, the other routes do not involve injection into muscle tissue. The topical route involves applying medication directly onto the skin or mucous membranes for localized effects. The intravenous route entails injecting medication directly into the bloodstream via a vein, providing immediate systemic effects. The subcutaneous route involves injecting medication into the tissue layer between the skin and muscle, which allows for slower absorption compared to the intramuscular route. Each of these routes has its particular applications, benefits, and absorption characteristics, making the intramuscular route distinctive for its specific application to muscle tissue.