Final answer:
Bioavailability refers to the proportion of a drug that enters systemic circulation and is affected by the route of administration, drug properties, and metabolic factors. It must be carefully managed due to its influence on efficacy and potential toxicity.
Step-by-step explanation:
The correct statement regarding bioavailability is that it is the proportion of the drug that reaches the systemic circulation. Bioavailability is indeed influenced by the route of administration, with intravenous administration typically resulting in higher plasma levels compared to oral or intramuscular administration.
Furthermore, higher bioavailability does not necessarily imply better drug effectiveness as it must be carefully balanced against potential for toxicity and side effects.
When bioavailability is poor with GI absorption, parenteral administration is preferred. Also, different drugs present specific pharmacokinetic characteristics, such as varying half-lives and dose-dependence, which can influence the appropriate dosing and frequency of administration. Efforts to enhance oral bioavailability might include modifying physiochemical properties of the compound to improve passive diffusion, while at the same time keeping in mind the drug's solubility, permeability, and metabolic stability.