The following article has been authored by John Heaney.
Deaeration, or degassing, of dissolution media is not required for every dissolution method, but when it is required it is critically important. The USP Prednisone PVT requires deaeration of the dissolution media and the tablet is formulated to show whether or not the deaeration method is adequate. Deaeration tends to have a larger impact on dissolution results as compared to other factors regarding the dissolution test. How this shows itself can change depending both on the apparatus, and the dosage being tested.
How to deaerate is largely up to the lab, and most deaeration methods are fine so long as they are properly validated with development and validation of the dissolution method. Historically, Helium sparging was used but is less common now due to cost as well as studies showing that while the oxygen was removed from the media, the overall content of gases did not drop significantly. Sonication may be used as well when used in combination with higher temperatures and/or keeping the media under vacuum. The USP method is frequently used and performs well but is labor intensive. Several automated solutions are available from dissolution bath manufacturers which both perform well while simultaneously speeding up the process.
How poor deaeration can show itself will depend primarily on the dosage form and to some extent the apparatus.
If the dosage form disintegrates it is more likely to have the dissolution values driven high. The reason is the air bubbles in the media, which may not be visible, will attach to the particles of the dosage form and help them float within the vessel. For both paddles and baskets, this can result in higher dissolution values as the floating particles increase the surface area available for the API to enter into solution.
If the dosage form is non-disintegrating, then it is possible that the bubbles may adhere to the surface of the tablet and reduce the amount dissolved. However, this may vary depending on both the dosage form and the degree to which the media has been deaerated.
Poor deaeration interfering with the function of the dissolution apparatus is less common but still possible. In the case of baskets, it has the potential to block holes in the mesh which allow the drug to leave the basket, reducing results. With the paddle method, if a sufficient amount of bubbles cover the paddle it may effectively change the dimensions and the hydrodynamics within the vessel. However, these would both be considered very niche cases as it would mean the dosage form itself was minimally affected while the apparatus was significantly affected.
Ensuring the deaeration method is sufficient should be done during the development of the dissolution method. Ensuring the deaeration is performed properly needs to be done for each test run as failure to do so may cause significant time and resources to be dedicated to an investigation.