When we do Dissolution Method and Formulation Development, we are looking to gain as much information as quickly as possible. One technique which can help gain insights without much additional work is the infinity spin (also called the final spin). The infinity spin is an additional timepoint to your dissolution method where you increase the RPM to 200-300 RPM. We basically turn our dissolution unit into a blender to maximize extraction from our formulation. So - what can this tell us during development?
If we find that we have lower dissolution results than expected/desired but achieve near 100% after the infinity spin, then this may indicate your dissolution method needs greater mixing. Some common reasons for low results in method development might be coning issues, tough sample matrixes like HPMC capsules, or formulation issues. In this case, I would usually try to perform the dissolution again at a higher RPM and evaluate results. If you're already operating at a high RPM speed (75-100 RPM) then this likely indicates a formulation issue or a product that needs a different type of agitation. HPMC capsules, chewable tablets, etc. might benefit from a stationary basket over paddle method or Apparatus 3 for example.
If we perform the infinity spin and still have low results, then this almost always points to a formulation issue. A product that isn't achieving almost full results at very high RPM speeds are likely to not open with greater agitation or perhaps not even contain the full amount of drug at all. You can confirm the amount of drug in this lot of product by looking at Assay or Content Uniformity results.
Infinity spins are just one additional time point during our dissolution method development and can really help you gain a lot of information about your methods and products more quickly. If you take observations (and I hope you do), you'll gain even more insight into why your product is behaving the way it is.
Read also: What is Q-Value in Dissolution Specification
Resource Person: Ken Boda (Dissolution Product Specialist at Agilent Technologies)
