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Why 900 ml in Dissolution?

Published in Dissolution Testing 2 mins read

The use of 900 ml as the dissolution media volume is primarily to achieve sink conditions, ensuring complete and unimpaired dissolution of the drug substance.

Understanding Sink Conditions

  • Definition: Sink conditions refer to a situation where the volume of the dissolution medium is sufficient to dissolve a high amount (typically three times) of the drug substance without approaching saturation.

  • Importance: When sink conditions are met, the dissolution rate is not limited by the drug's solubility, allowing for a more accurate assessment of the drug product's release characteristics. If the concentration of the dissolved drug approaches its saturation solubility, the dissolution rate may slow down or cease entirely, providing misleading data.

Why 900 ml Specifically?

While 900 ml is a common volume, the actual volume required to achieve sink conditions depends on the drug substance's solubility and dose. However, 900 ml (or 1 liter) is often chosen because:

  • Generality: For many drug products and doses, 900 ml provides adequate sink conditions. It's a standardized volume often specified in pharmacopeial monographs.

  • Historical Reasons: The volume has been used extensively over time and become a standard practice within the pharmaceutical industry.

  • Practical Considerations: 900 ml is a manageable volume for standard dissolution apparatus.

When are Other Volumes Used?

  • 500 ml: Sometimes used when sink conditions are achieved with this smaller volume and the measurable level of the drug is low enough for analytical detection.

  • Other Volumes: Volumes other than 900 ml might be used if justified by the specific solubility and dose characteristics of the drug product. The key is to demonstrate that sink conditions are maintained.

Factors Influencing Media Volume Selection

  • Drug Solubility: Lower solubility generally necessitates a larger dissolution volume to maintain sink conditions.

  • Drug Dose: Higher doses require a larger dissolution volume.

  • Analytical Sensitivity: The chosen volume must result in drug concentrations that are high enough to be accurately measured by the analytical method.

In Summary

The 900 ml volume used in dissolution testing is primarily driven by the need to establish sink conditions, ensuring that the dissolution process accurately reflects the drug product's release characteristics without being artificially limited by solubility constraints. While 900 ml is a common standard, the appropriate volume depends on the drug's properties and must be justified by maintaining sink conditions.