Question

The rate and extent of absorption of a drug from a dosage form as determined by its concentration-time curve in blood or by its excretion in urine is referred as:

• A. Distribution
• B. Bioavailability
• C. Redistribution
• D. Plasma protein binding

Hint:

- Intravenous (IV) administration has a bioavailability of exactly 100% (\(F = 1.0\)), as the absorption step is entirely bypassed.
- All other routes (oral, intramuscular, subcutaneous) have a bioavailability of $\le$ 100% due to incomplete absorption and first-pass metabolism.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Pharmacokinetics describes the movement of a drug through the body, divided into absorption, distribution, metabolism, and excretion (ADME).

Step 2: Detailed Explanation:
Let us define the options to identify the correct pharmacokinetic parameter:
- Distribution: The reversible transfer of a drug from the systemic circulation into the interstitial and intracellular fluids.
- Bioavailability (F): The rate and extent to which the active drug ingredient is absorbed from its formulation and becomes available in the systemic circulation.
It is calculated by comparing the Area Under the Curve (AUC) of a non-intravenous dose to the AUC of an intravenous dose:
\[ F = \frac{\text{AUC}_{\text{oral}}}{\text{AUC}_{\text{IV}}} \times 100 \]
- Redistribution: The movement of a highly lipophilic drug from its highly perfused site of action (like the brain) to less perfused storage tissues (like fat), terminating its clinical effect.
- Plasma protein binding: The association of a drug with blood proteins like albumin, rendering the bound fraction pharmacologically inactive.

Step 3: Final Answer:
Therefore, the rate and extent of drug absorption is defined as bioavailability.