How are acidic drugs extracted from a solution?

• A. Not easily extracted; require basification
• B. Easily extracted from an alkaline solution with organic solvents
• C. Easily extracted from an acidified water solution with organic solvents
• D. They cannot be extracted.

Answer: (C)

Acid-base partitioning governs how drugs move between water and organic solvents. An acidic drug exists mainly as the non-ionized form (HA) in acidic conditions and as the ionized form (A−) when the solution is neutral or basic. The non-ionized form is more soluble in organic solvents, while the ionized form stays in the aqueous phase.

To extract an acidic drug efficiently into an organic solvent, you acidify the aqueous solution. Lowering the pH shifts the equilibrium toward the non-ionized HA form, which readily partitions into the organic solvent. If the solution is alkaline, the drug becomes A− and remains in water, making extraction into the organic phase poor.

Thus acidifying the water enhances extraction into an organic solvent. The other scenarios—basification or alkaline conditions—would hinder extraction for an acidic drug, and saying it cannot be extracted is incorrect.