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

BCS classification depends on two yes or no questions: does the highest dose dissolve fully in 250 mL of aqueous medium across pH 1 to 6.8, and does the drug get absorbed well across the intestinal wall (generally taken as 90 percent or more to count as high permeability).

1. Class I: Needs a yes to both questions. The drug dissolves fully, which is a yes, but its 85 percent absorption is a no for high permeability, so Class I is out.
2. Class II: Needs low solubility with high permeability. Complete dissolution in 250 mL already fails the low-solubility requirement.
3. Class III: Needs high solubility with low permeability. Complete dissolution gives the yes for solubility, and 85 percent absorption, being under the high-permeability bar, gives the no for permeability. Both conditions line up with this class.
4. Class IV: Needs low solubility and low permeability together. Since the drug dissolves completely, the solubility condition fails here too.

Working through the two questions in order leaves only one class standing.

So the correct answer is Class III.