injection

An injection is the most familiar form of parenteral: a sterile preparation pushed into the body through a needle and syringe. Think of it as a single sharp delivery rather than a slow drip — a measured shot that places the drug exactly where it is needed.

Injections come as ready-to-use solutions, as suspensions of fine drug particles, as emulsions, or as dry powders that are reconstituted with a sterile diluent just before use. The vehicle is usually water for injection, but oily vehicles are used for drugs meant to be released slowly from a muscle depot. Each injection is labelled with the route for which it is intended, because what is safe to give into a muscle may be unsafe to give into a vein.

The common routes are intravenous, directly into a vein for immediate full effect; intramuscular, into muscle for a moderately fast and sustained effect; and subcutaneous, into the fatty layer under the skin for slower absorption. Less common routes include intradermal, intra-articular and intrathecal.

An honest limitation: injections require trained hands, carry a risk of infection and tissue damage, cannot easily be reversed once given, and are uncomfortable for patients — so they are reserved for situations where oral dosing will not work.