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Published on: May 1, 2018
Impact of density gradients on flow-through dissolution in a cylindrical flow cell
Larry E Stevens1, Paul J Missel
1Alcon Research Ltd, Fort Worth, TX 76134, USA.
Pharmaceutical Development and Technology
|November 15, 2006
Summary
Density gradients can affect drug release rates at slow flow rates. Simulations and experiments show these gradients alter dissolution rates, especially with changes in flow direction or cell orientation.
Area of Science:
- Pharmacokinetics and Drug Delivery
- Computational Fluid Dynamics
- Materials Science
Background:
- Accurate measurement of drug release rates for sparingly soluble compounds necessitates slow eluent flow rates.
- Indefinitely reducing flow rate is limited by potential density gradient-induced alterations in drug release.
- Understanding these density gradient effects is crucial for reliable dissolution testing.
Purpose of the Study:
- To investigate the impact of concentration-dependent density gradients on drug release rates.
- To simulate and experimentally validate the influence of flow rate, direction, and orientation on dissolution.
- To provide insights into optimizing conditions for measuring release rates of sparingly soluble compounds.
Main Methods:
- Finite element simulations of convective diffusion and dissolution incorporating concentration-dependent density gradients.
- Comparison of simulation results with experimental data obtained using a modified flow cell.
- Experimental validation using an implant obstruction in a cylindrical flow cell.
Main Results:
- Simulations accurately reproduced literature trends of dissolution rate changes with eluent flow rate.
- Observed changes in dissolution rate correlated with flow direction and sample cell orientation.
- Experimental reproduction confirmed the influence of density gradients under varied conditions.
Conclusions:
- Concentration-dependent density gradients significantly influence drug release rates at low flow conditions.
- Flow direction and gravitational effects, mediated by density gradients, must be considered in dissolution testing.
- The findings offer a better understanding for designing and interpreting drug release studies, particularly for poorly soluble drugs.
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