In pharmaceutical R&D, dissolution testing plays a vital role in predicting drug release and bioavailability. While most studies are conducted under sink conditions to ensure the concentration of dissolved drug remains well below its saturation solubility, sometimes we deliberately test under non-sink conditions.
What are Non-Sink Conditions?
Non-sink conditions occur when the dissolution medium is near or at saturation, meaning the drug concentration approaches its solubility limit. In such cases, further dissolution is restricted, and the rate is influenced not only by formulation and surface area but also by the solubility barrier.
Why Perform Dissolution Under Non-Sink Conditions?
- Realistic simulation of in vivo environments, especially for poorly soluble drugs.
- Formulation discrimination – helps identify subtle differences in release profiles that might be masked under sink conditions.
- Stress testing of formulations for robustness, especially in biorelevant media.
- Evaluation of precipitation tendencies for supersaturated systems.
Key Considerations:
- Select appropriate medium volume & composition to achieve desired saturation.
- Monitor for precipitation and polymorphic changes.
- Interpret data carefully, as dissolution rate will plateau faster than in sink conditions.
In short, non-sink dissolution testing is a powerful tool for deeper understanding of formulation behavior, especially for BCS Class II and IV drugs. While sink conditions are ideal for QC and batch release, non-sink studies add scientific value during early development and bio-predictive testing.
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Resource Person: Vijay Agrawal