Question

5-fluorouracil is absorbed by

• A. Passive diffusion
• B. Active transport
• C. Pinocytosis
• D. Ion pair absorption

Hint:

For many lipophilic drugs like 5-fluorouracil, passive diffusion is the key absorption mechanism due to the concentration gradient.

Answer 1

The Correct Option is A

Step 1: Understanding 5-fluorouracil absorption.
5-fluorouracil, a chemotherapeutic agent, is absorbed primarily via passive diffusion, which occurs due to its lipophilic properties and concentration gradient across cell membranes.
Step 2: Analyzing the options.
(1) Passive diffusion: Correct — Passive diffusion is the most common mechanism for absorption of 5-fluorouracil.
(2) Active transport: Incorrect, 5-fluorouracil does not require energy or a carrier for absorption.
(3) Pinocytosis: Incorrect, this is not a typical mechanism for absorption of 5-fluorouracil.
(4) Ion pair absorption: Incorrect, 5-fluorouracil does not rely on ion pair absorption.
Step 3: Conclusion.
5-fluorouracil is absorbed by (1) Passive diffusion.

Answer 2

Drug absorption across the gastrointestinal membrane can occur through several mechanisms depending on a drug's physicochemical properties. Let's evaluate each option for 5-fluorouracil.

1. Passive diffusion: 5-fluorouracil is a small, moderately lipophilic molecule that can cross biological membranes down its concentration gradient without requiring energy or a specific carrier, which is the defining feature of passive diffusion.
2. Active transport: Active transport requires a specific carrier protein and energy expenditure to move a drug against its concentration gradient, which is not the primary mechanism described for this drug's absorption.
3. Pinocytosis: Pinocytosis involves the cellular engulfment of fluid droplets and is typically relevant to large molecules or particulates, not a small molecule like 5-fluorouracil.
4. Ion pair absorption: Ion pair absorption applies to highly ionized drugs that pair with an oppositely charged species to cross membranes, which is not the mechanism relevant here.

Given its small size and lipophilicity, passive diffusion down the concentration gradient is the mechanism that fits 5-fluorouracil's absorption.

Therefore, the correct answer is Passive diffusion.