Drug dissolution testing is routinely carried out as a tool to evaluate batch-to-batch reproducibility for quality control (QC) purposes, as required by Food and Drug Administration (FDA) (Phillips et al., 2012) (European Pharmacopoeia PE, Sirasitthichoke et al., 2021a, Sirasitthichoke et al., 2021bb) and to establish in vivo-in vitro correlations. In addition to regulatory requirements, dissolution testing is used to evaluate formulations with different drug release profiles during drug formulation development (Wang and Armenante, 2016, Wang et al., 2018). The United States Pharmacopeia (USP) dissolution apparatuses are the most widely used in vitro systems , as currently described in USP general chapter Dissolution 〈7 1 1〉 (USP. Dissolution <711>. Rockville, MD: In: USP-NF; 2023.). The use of these apparatuses and the associated methods are intended to provide the most discriminatory approaches to differentiate subtle drug formulations and to enable filing with the regulatory agencies. The testing results depend on the drug product (i.e., solid-state of active pharmaceutical ingredient (API), inactive substances or excipients, drug release mechanism, tablet physical properties), the dissolution media properties, and the hydrodynamic performance of the apparatus restricted by the setup and/or component of the device. Several studies have demonstrated that the geometry and operation of the test apparatus can alter the prevailing hydrodynamics, thus contributing to increasing the level of variability and inconsistency in dissolution testing results, extensively evidenced in USP paddle Apparatus 2 (McCarthy et al., 2003, McCarthy et al., 2004, Mirza et al., 2005, Wang and Armenante, 2012, Ameur and Bouzit, 2013, Bai et al., 2007, Bai et al., 2007, Bai and Armenante, 2008, Bai and Armenante, 2009). However, few studies have been devoted so far to the hydrodynamic characterization of USP Apparatus 1 (Sirasitthichoke et al., 2021a, Sirasitthichoke et al., 2021b, Diebold and Dressman, 2001, Martinez et al., 2020). The USP rotating basket dissolution testing Apparatus 1 has been one of the preferred dissolution testing tools, especially for the immediate release (IR) of oral solid dosage forms (Davanço et al., 2020). The apparatus consists of a spherical bottom-shaped glass vessel that contains the dissolution medium in which a metal wire basket with mesh opening typically varying from 10 to 40 mesh (more rarely 100 mesh) rotates (Sirasitthichoke et al., 2021a). In recent studies, our group has quantified the velocity distribution using a standard basket 40-mesh size operated at different basket rotational speeds in a vessel filled with 900 mL (Sirasitthichoke et al., 2021b) and 500-mL (Sirasitthichoke et al., 2022) of water. We found that the velocities in Apparatus 1, when filled with 500-mL of liquid volume, were similar to those in the 900-mL case in some portions of the vessel but not in others, including a significantly more intense and downward-inclined radial jet flow in the 900-mL filled vessel vs. to the 500-mL case. A recent study on hydrodynamics in the 900-mL vessel with different basket mesh sizes was also conducted (Sirasitthichoke et al., 2021a) using the most commonly used basket openings (i.e., 10-, 20-, and 40-mesh sizes).

That study showed that the use of different basket geometries at 100 rpm in a 900-mL filled volume greatly affects the velocity distribution, especially below the basket and in the lower region of the vessel (Sirasitthichoke et al., 2021a). In general, the magnitude of the velocities increased with increasingly larger mesh openings in the basket. Although those studies provide the detailed hydrodynamics inside the USP Apparatus 1, there is still a need for additional work on this system, especially for the other fill volume also commonly used in dissolution testing (500 mL) in combination with baskets of different opening sizes. This is especially critical for low-dose drugs since the analytical method must be sensitive enough to evaluate the amount of dissolved drug released from the dosage forms (Scheubel et al., 2010).

Therefore, the objective of this work was to experimentally quantify the hydrodynamics of a USP Apparatus 1 equipped with baskets of different mesh sizes, i.e., 10-, 20-, and 40-mesh, rotating at 100 rpm in a 500-mL liquid volume. The results obtained here were compared with those of our previous work with a 900 mL-filled vessel (Sirasitthichoke et al., 2021a) to investigate the effect of media fill volume on the system’s hydrodynamics.