Which USP dissolution apparatus is used for tablets and granules?

• A. Apparatus II (Paddle) for tablets/capsules
• B. Apparatus I (Basket) for tablets/granules
• C. Apparatus III (Reciprocating Cylinder) for poorly soluble or controlled-release forms
• D. Apparatus IV (Flow-through) for insoluble or highly permeable compounds and non-traditional dosage forms

Answer: (B)

The question tests which USP dissolution approach best fits solid dosage forms like tablets and granules. The basket apparatus is designed to hold the solid dosage form inside a mesh basket that stays in the dissolution medium, exposing the surface to the fluid on all sides while preventing loss of material. This setup provides a defined surface area and reproducible contact with the dissolution medium, which is ideal for tablets and granules that may not suspend well or could escape if simply stirred.

In contrast, the paddle method is typically used when the dosage form can be freely submerged and stirred, such as tablets or capsules that readily disperse or suspend. The other two apparatuses are reserved for special cases: reciprocating cylinder for poorly soluble or controlled-release forms that need specific hydrodynamics, and flow-through for insoluble or highly permeable compounds and non-traditional dosage forms. So for tablets and granules, the basket apparatus is the appropriate choice.