Question

An antibiotic dissolves completely in 250 mL of aqueous solution at pH range 1–6.8 and 37°C, and after dissolution, it shows 85% absorption in the body. Based on the Biopharmaceutics Classification System (BCS), in which class does this drug belong?

• A. Class I
• B. Class II
• C. Class III
• D. Class IV

Hint:

BCS classification aids in predicting drug absorption and guiding formulation strategies. Class III drugs often require permeability enhancement techniques.

Answer 1

The Correct Option is C

The Biopharmaceutics Classification System (BCS) categorizes drugs based on their solubility and intestinal permeability:
- Class I: High solubility, high permeability
- Class II: Low solubility, high permeability
- Class III: High solubility, low permeability
- Class IV: Low solubility, low permeability
Key points from the question:
- The drug dissolves completely in 250 mL aqueous solution over a pH range 1–6.8 at 37°C, indicating high solubility.
- The drug shows only 85% absorption, which suggests low permeability (high permeability is generally $>$85% absorbed, but borderline values and context suggest moderate to low permeability).
Thus, the drug fits the profile of Class III, which is characterized by high solubility but low permeability.

Answer 2

The Biopharmaceutics Classification System sorts a drug into one of four classes using two properties only: how well it dissolves in water and how well it crosses the gut wall into the blood. Reading the two clues in the question against this grid gives the class directly.

1. Class I (high solubility, high permeability): This class needs both a fully dissolving drug and strong absorption, typically above 90 percent. The drug here dissolves completely, but its absorption of 85 percent falls short of the high-permeability cutoff, so Class I does not fit.
2. Class II (low solubility, high permeability): This class describes drugs that struggle to dissolve at all across the physiological pH range. Since this drug dissolves completely in 250 mL from pH 1 to 6.8, it clearly has high, not low, solubility, ruling this class out.
3. Class III (high solubility, low permeability): Complete dissolution across the gut's pH range signals high solubility, while 85 percent absorption sits below the threshold generally used to call a drug highly permeable. High solubility paired with borderline-to-low permeability is exactly the Class III profile.
4. Class IV (low solubility, low permeability): This class needs poor dissolution as well as poor absorption. The complete dissolution reported here rules out low solubility, so Class IV does not apply.

Matching 'dissolves completely' to high solubility and '85 percent absorption' to the low-permeability side of the cutoff places the drug in one class only.

So the correct answer is Class III.