ABSTRACT
The term parenteral drug delivery covers a number of administration routes, which have little in common other than the fact that they generally involve the use of a hypodermic needle to inject the drug into the body. This route bypasses a number of physiological barriers and hence the constraints on the composition and formulation of the medicine are much more rigorous than for less invasive routes such as oral or transdermal delivery. Despite this a surprising range of materials can be injected into various tissues if the appropriate precautions are taken. We will examine the constraints for specific formulations with respect to the appropriate physiological route, but a number of general principles are common to all routes. The most important is that the formulation must be sterile, since the major defence mechanisms of the body (the skin and mucous membranes) are bypassed, and so any infective agent in the formulation may cause major disease. It is not only necessary to remove live microorganisms; parts of dead organisms can elicit an immune response, and polysaccharides from the bacterial cell wall, known as pyrogens, can cause a substantial increase in body temperature.
