Which dissolution apparatus is used for insoluble or highly permeable compounds and non-traditional dosage forms?

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

Answer: (A)

The test is about matching the dissolution method to the drug’s physical properties and the dosage form. For drugs that are insoluble or very permeable, and for non-traditional dosage forms, you need a system that can provide sink conditions and flexible hydrodynamics. The flow-through dissolution apparatus does exactly that: it continuously pumps dissolution medium through a cell containing the dosage form, so the medium is refreshed as dissolution occurs. This keeps the dissolved drug concentration well below saturation, which is crucial for accurately measuring dissolution of poorly soluble compounds. For highly permeable drugs, the flowing medium rapidly removes the dissolved drug, reducing the boundary layer effects and simulating intestinal flow, yielding a more representative dissolution rate. The flow-through design also accommodates non-traditional dosage forms that don’t fit well in a basket or paddle setup, since the sample is exposed to a controlled, moving stream rather than static agitation. Therefore, this method is best suited for insoluble or highly permeable compounds and non-traditional dosage forms.