The following article has been authored by John Heaney.
Compared to dissolution Apparatus 1 (Baskets) and Apparatus 2 (Paddles), Dissolution Apparatus 3: Biodissolution (the reciprocating cylinder) is quite rare. However, it has some key advantages over the more common baskets and paddles which can make it very useful for key applications.
Apparatus 3 consists of a glass cylinder with a mesh screen at the bottom moving up and down in a specified distance and rate within a glass dissolution vessel. The dosage form is held within the glass cylinder. Vessels are typically arranged in rows allowing the glass cylinder to be moved by automation from row to row during the test.
This design allows for a few big advantages over Apparatus 1 and 2.
Extended-Release:
While there are several rows of vessels for each dosage to cycle through, it is not required that they all contain the same media. In fact, in the case of extended-release dosage forms, it’s better to have the media at different pH from row to row. The design of Apparatus 3 facilitates easy pH changes. Instead of draining and refilling a vessel or temporarily stopping the test with Apparatus 1 or 2 to swap vessels; Apparatus 3 simply moves the cylinder to the next row.
Low Solubility or Low Dose Drugs:
Dosage forms with low or hard to detect API’s can also benefit from Apparatus 3. The typical volume in each vessel is around 150mL to 200mL. This normally can’t be done with Apparatus 1 or 2 as it would require moving to small volume dissolution apparatus which are non-compendial; which means a significantly higher workload in method development to ensure the different apparatus is fully justified and providing consistent results. Apparatus 3 has an advantage here as it is a compendial device, and so long as the dissolution method is proven to be sufficiently discriminatory no additional work to justify different apparatus would be required.
An important point to keep in mind is dissolution methods between Apparatus 1 or 2, and Apparatus 3 are not interchangeable. The specifications found in monographs are entirely different and there is no way to equate them. This means that if you are looking to create a generic equivalent of a product developed on the reciprocating cylinder, you will likely need to invest in an Apparatus 3 instrument. If you’re an innovator this can also be used to make your formulation harder to replicate.
Apparatus 3 is a unique but recognized design that offers some big benefits for certain situations. While it is rare compared to Apparatus 1 and 2, it should not be overlooked when developing extended-release, low dose, or low solubility products.
Notes on APP 3:
- Mesh in bottom of basket can clog just like regular basket
- Agitation method can help some dosage forms disperse better
- Can easily change media or pH by moving to next row of instrument
- Can be touchy with surfactants due to type of agitation
- Strictly mechanical qualification at the moment as no reference standard (e.g. prednisone) exists for APP 3
- Smaller volumes, typically around 200-300mL per vessel
- Can easily be adapted to USP APP 7
- Good choice for low dose compounds with reduced volume
- Can be used with capsules, beads, other extended-release dosages
- Great for extended-release due to simplified pH changes
- Not interchangeable with APP 1 or 2
