Determining the significance of deaerating the dissolution medium is essential because air bubbles can create barriers in the dissolution process when present on the dosage unit or basket mesh, leading to unreliable test results. Moreover, bubbles can cause particles to adhere to apparatus and vessel walls.
Bubbles on the dosage unit might increase buoyancy, resulting in a faster dissolution rate, or decrease the available surface area, leading to a slower dissolution rate. Poorly soluble drugs are particularly sensitive to interference from air bubbles, making deaeration necessary for testing such products.
There are various methods for deaeration, with a footnote in the Procedure section of USP <711> describing a typical process involving heating, filtering, and applying a vacuum. The extent of deaeration can be assessed by measuring total dissolved gas pressure or dissolved oxygen concentration. Surfactant-containing media are usually not deaerated due to excessive foaming, but sonication or deaeration before adding surfactants can be effective.
To determine the need for deaeration, compare results from samples run in non-deaerated and deaerated media. If deaeration shows no effect, it can justify its omission in future tests.
However, if there is an effect, careful control and characterization of the deaeration process are necessary, as the dissolved gas content of deaerated media under atmospheric pressure is unstable and tends toward saturation. Stirring or pouring deaerated medium can increase the rate of redissolving atmospheric gases.
Read also: Selection of Dissolution Medium for Solid Oral Drug Products
