What is drug bioavailability?

What is drug bioavailability?

• A. The fraction of unchanged drug reaching the systemic circulation following administration
• B. The rate and extent to which the active ingredient/moiety becomes available at the site of action
• C. The fraction of the drug that is excreted unchanged
• D. The amount of drug that is metabolized before reaching systemic circulation

Answer: (A)

Bioavailability is the fraction of the administered dose that reaches the systemic circulation in unchanged form. It reflects how much of the drug actually gets into the blood and is available to have an effect, with intravenous administration providing the full amount (100%) since it bypasses absorption barriers. For other routes, the value is less than 1 due to absorption limitations and first-pass metabolism. The other descriptions describe either the speed at which the drug becomes available at the site of action, the amount excreted unchanged, or pre-systemic metabolism, none of which define the actual amount of unchanged drug reaching circulation.

Bioavailability is the fraction of the administered dose that reaches the systemic circulation in unchanged form. It reflects how much of the drug actually gets into the blood and is available to have an effect, with intravenous administration providing the full amount (100%) since it bypasses absorption barriers. For other routes, the value is less than 1 due to absorption limitations and first-pass metabolism. The other descriptions describe either the speed at which the drug becomes available at the site of action, the amount excreted unchanged, or pre-systemic metabolism, none of which define the actual amount of unchanged drug reaching circulation.