Final answer:
Medication that is not well absorbed through the GI tract or that requires fast systemic effects is often given by parenteral routes like intravenous or intramuscular injections, bypassing the alimentary canal and ensuring higher plasma drug levels.
Step-by-step explanation:
When medication cannot be absorbed through the gastrointestinal (GI) tract or more immediate absorption into the bloodstream is required, it is commonly administered by a parenteral route, such as intravenous (IV) or intramuscular (IM) injection. This method bypasses the alimentary canal and ensures that drugs with poor oral bioavailability or those requiring quick systemic effects achieve the necessary plasma levels efficiently. An example is the administration of certain vaccines, which are often delivered by injection into the arm to elicit a quick and effective immune response. Other routes like oral administration of the polio vaccine or intranasal influenza vaccines highlight how drug efficacy and patient compliance can be enhanced with alternative delivery methods. Moreover, some anesthesia procedures combine inhalational anesthetics with intravenous injections to both induce and maintain anesthesia due to the hydrophobic properties of the anesthetic agents.