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. Bioequivalence
• B. Distribution
• C. Redistribution
• D. Bioavailability

Hint:

Remember: "Bioavailability" refers to a single drug's availability in systemic circulation, while "Bioequivalence" is a comparison of bioavailability between generic and brand-name drugs.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Pharmacokinetics deals with the quantitative study of drug movement in, through, and out of the body.
When a drug is administered via any route other than direct intravenous injection, it must be absorbed into the systemic circulation.
Evaluating the efficiency of this absorption process requires measuring both how quickly (rate) and how much of (extent) the active drug reaches the systemic blood flow.

Step 2: Detailed Explanation:
Let us define the terms presented in the options:
1. Bioavailability (D):
This is defined as the rate and extent to which the active drug ingredient or therapeutic moiety is absorbed from a drug product and becomes available at the site of drug action.
In clinical practice, it is calculated by comparing the Area Under the Curve (AUC) of a non-intravenous dose with that of an intravenous dose:
\[ F = \frac{\text{AUC}_{\text{oral}} \times \text{Dose}_{\text{IV}}}{\text{AUC}_{\text{IV}} \times \text{Dose}_{\text{oral}}} \] It is measured using plasma drug concentration-time curves or by analyzing the cumulative excretion of unchanged drug in urine over time.
This matches the definition provided in the question.
2. Bioequivalence (A):
This refers to the comparison of bioavailabilities between two different drug formulations of the same active ingredient.
Two formulations are bioequivalent if their rate and extent of absorption show no significant statistical difference when administered under similar conditions.
3. Distribution (B):
This is the reversible transfer of a drug between one compartment (such as blood) and another (such as interstitial and intracellular fluids).
4. Redistribution (C):
This is the highly lipid-soluble drug movement away from highly perfused tissues (like the brain) to less perfused tissues (like skeletal muscle and adipose tissue), which terminates the drug's effect.

Step 3: Final Answer:
The rate and extent of drug absorption reaching systemic circulation is defined as bioavailability.
Therefore, the correct option is (D).