Biorelevant Dissolution Method Considerations for the Appropriate Evaluation of Amorphous Solid Dispersions: are Two Stages Necessary?

Abstract

Biorelevant dissolution testing has been widely used to better understand a drug or formulation's behavior in the human gastrointestinal (GI) tract. The successful evaluation of biorelevant dissolution behavior requires recognizing the importance of utilizing suitable biorelevant media in conjunction with an appropriate dissolution method, especially for supersaturating drug delivery systems, such as amorphous solid dispersions (ASDs). However, most conventional biorelevant dissolution testing methods are not able to accurately reflect the dissolution, supersaturation, and precipitation tendencies of a drug or formulation, which could misinform ASD formulation screening and optimization. In this study, we developed a single compartment 2-stage pH-shift dissolution testing method to simulate the changes in pH, media composition, and transit time in the GI tract, and results were compared against the conventional single compartment 1-stage dissolution method. Nine model drugs were selected based on their ionization properties (i.e. acid, base or neutral) and precipitation tendency (i.e. moderate or slow crystallizer). The dissolution results confirmed that 2-stage pH-shift dissolution is the preferred biorelevant dissolution method to assess non-ionized weak base (nifedipine) and neutral (griseofulvin) compounds exhibiting a moderate precipitation rate from solution when formulated as ASDs. Finally, we designed a flowchart guidance for the appropriate biorelevant dissolution performance characterization of different categories of ASD formulations.

Keywords: Amorphous solid dispersion; Crystallization; Dissolution; Duodenum, Jejunum; Gastrointestinal; In vitro model; Precipitation; Spray drying; Supersaturation.