Which route of administration involves using a needle and syringe?

The route of administration that involves using a needle and syringe is injected. This method is characterized by the direct introduction of a substance, such as medication or a drug, into the body through the skin or a mucous membrane. It can involve different forms of injection, such as intravenous, intramuscular, or subcutaneous, depending on the desired effect and the substance being administered.

In contrast, oral administration refers to taking substances by mouth, inhalation involves breathing in substances through the respiratory system, and topical application involves placing substances directly onto the skin or mucous membranes for localized effects. Each of these methods has its specific use and absorption rates, but none involve the use of a needle and syringe, which is unique to the injected route.