An improved method for the characterization of supersaturation and precipitation of poorly soluble drugs using pulsatile microdialysis (PMD).

In current pharmaceutical drug discovery, most candidates are poorly soluble in water, which can result in poor bioavailability. To overcome this problem, formulations that create supersaturation of the drug are a well-studied alternative. Characterizing the dissolution from these systems is challenging because conventional methods, such as sampling with a syringe then filtering with a 0.2-0.45 μm filter before an HPLC assay, can overestimate the concentration of dissolved drug by allowing nuclei or small precipitated particles to pass, which then dissolve in the HPLC mobile phase. Nuclei and small particles can also cause overestimation of the dissolved concentration when using optical methods. Such overestimations can lead to failure of in vivo prediction of drug bioavailability from supersaturated systems. This paper reports a novel method to determine the free dissolved drug concentration in a dissolution medium using pulsatile microdialysis (PMD). Ibuprofen was used as a model drug for determining precipitation and supersaturation. Supersaturation was induced chemically by changing pH, and also by dissolution/release from an in-house formulation. The adaptation of a previously developed PMD model is summarized, and experimental results comparing dissolved concentrations determined using PMD and direct sampling by syringe and filtering are presented.