Final answer:
The first-pass effect reduces a drug's concentration due to the liver's metabolization, so such drugs are typically given by the parenteral route, such as intravenous or intramuscular injection, to bypass the GI tract and liver metabolism.
Step-by-step explanation:
Drugs that undergo the first-pass effect are typically administered by routes that avoid the gastrointestinal (GI) tract, such as the parenteral route (intravenous or intramuscular injection). This circumvents the reduction in drug concentration due to metabolism in the liver when a drug is absorbed from the GI tract. The first-pass effect refers to the significant metabolization or elimination of a drug when it first passes through the liver after being absorbed from the digestive system, resulting in a reduced concentration of the active drug reaching the bloodstream.
When a drug is not readily absorbed in the GI tract, or when avoiding the first-pass effect is necessary, administration by the parenteral route is preferred, commonly in health-care settings. Intravenous administration often leads to substantially higher plasma levels of the drug compared to oral or intramuscular routes, which is critical for treating serious infections where high systemic levels of the drug are required swiftly.