The USP specifies different types of dissolution apparatuses based on the characteristics of the drug product being tested.
USP Apparatus 1 - Basket Method
The basket method uses a cylindrical basket made of stainless steel mesh that holds the dosage form while rotating in the dissolution medium.
Best suited for:
- Capsules
- Floating dosage forms
- Beads and pellets
- Products that tend to disintegrate into large particles
USP Apparatus 2 - Paddle Method
The most commonly used method featuring a paddle that rotates in the dissolution vessel creating gentle agitation.
Best suited for:
- Immediate-release tablets
- Most solid oral dosage forms
- Suspensions
USP Apparatus 5 - Paddle Over Disk
Used primarily for transdermal patches where the product is held at the bottom of the vessel by a disk assembly.
Best suited for:
- Transdermal patches
- Medicated plasters
USP Apparatus 6 - Cylinder Method
Features a cylinder assembly for holding transdermal systems.
Best suited for:
- Transdermal therapeutic systems
- Large transdermal patches
Intrinsic Dissolution Testing
Measures the dissolution rate of a pure drug substance compacted into a non-disintegrating disk. This provides information about the drug's intrinsic properties independent of formulation factors.
Selecting the Right Method
The choice of apparatus depends on:
- Dosage form characteristics
- Drug release mechanism
- Regulatory requirements
- Historical data and bioequivalence considerations