Which statement correctly contrasts BCS Class II and Class IV drugs regarding dissolution strategies?

• A. Class II: low solubility, high permeability; Class IV: high solubility, high permeability.
• B. Class II: dissolution-limited; Class IV: combined solubility and permeability limitations.
• C. Class II: high solubility; Class IV: high permeability.
• D. Class II: low permeability; Class IV: low solubility.

Answer: (B)

In the BCS framework, the rate-limiting step for Class II drugs is dissolution because these compounds have low solubility but high permeability. Once dissolved, they cross membranes readily, so the overall absorption is governed by how fast the drug dissolves. Therefore, dissolution-focused strategies—such as reducing particle size, forming more soluble salt forms, creating solid dispersions or amorphous forms, and using surfactants or pH modifiers—are used to boost bioavailability.

For Class IV drugs, both solubility and permeability are poor, so absorption is limited by both processes. Improving dissolution alone won’t fully solve the problem because the drug still faces a significant barrier to permeation. Effective approaches must address both sides: enhancing solubility and improving permeability (through lipid-based formulations, absorption enhancers, prodrugs, or other permeability-boosting strategies).

Thus, describing Class II as dissolution-limited and Class IV as having combined solubility and permeability limitations captures the correct contrast in dissolution strategies.