Question

Arrange the routes of drug administration in the sequence that offer bioavailability from low to high:
(A) Intramuscular route
(B) Intravenous route
(C) Topical route
(D) Subcutaneous route
Choose the correct answer from the options given below:

• A. (B), (A), (C), (D).
• B. (D), (A), (C), (B).
• C. (C), (D), (A), (B).
• D. (C), (A), (D), (B).

Hint:

The intravenous route (B) always has a starting bioavailability of $100\%$ (the absolute highest), which means (B) must be the final element in the sequence. This immediately narrows down the options.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bioavailability refers to the rate and extent to which an active drug ingredient is absorbed from a drug product and becomes available at the site of drug action.
The route of administration is the most critical determinant of a drug's systemic bioavailability.
Detailed Explanation:
Let us analyze the bioavailability of the given routes:
- (C) Topical route: Primarily used for local effects on the skin or mucous membranes. Systemic absorption is highly restricted and slow, giving it the lowest systemic bioavailability among the options.
- (D) Subcutaneous (SC) route: Injecting into the subcutaneous fat layer leads to relatively slow, constant absorption due to lower vascularity than muscle.
- (A) Intramuscular (IM) route: Muscle tissue has a rich blood supply, allowing faster and more complete absorption of aqueous solutions compared to subcutaneous administration.
- (B) Intravenous (IV) route: Injecting a drug directly into the bloodstream bypasses all absorption barriers. By definition, its systemic bioavailability is $100\%$ ($1.0$).
Arranging these from lowest to highest bioavailability:
\[ \text{Topical (C)} \rightarrow \text{Subcutaneous (D)} \rightarrow \text{Intramuscular (A)} \rightarrow \text{Intravenous (B)} \] This corresponds to the sequence: (C), (D), (A), (B).

Step 2: Final Answer:
The correct low-to-high sequence matches Option (C).