(M1330-12-68) Establishing In Vitro-In Vivo Correlation of Amorphous Solid Dispersions

Purpose: Formulating amorphous solid dispersions (ASDs) for oral delivery is a commonly applied strategy to improve oral bioavailability by overcoming dissolution rate and/or solubility limitations of BCS class II drugs. While bioavailability enhancement of ASDs is well documented, establishing a predictive mathematical model describing in vitro-in vivo correlation (IVIVC) has often been a challenge [1,2]. Consequently, there is a need for further improvement of the predictability of in vitro studies to create a better preclinical foundation during drug development. Thus, the aim of the study was to establish IVIVC of four efavirenz (EFV) ASDs and crystalline EFV in a combined dissolution-permeation microFLUX setup based on the parallel artificial membrane permeability assay (PAMPA) principle.

Methods: Four polymers were included in the study, namely polyvinyl alcohol (PVOH), polyvinyl pyrrolidone vinylacetate (PVP VA64) and two grades (LF and MF) of hypromellose acetate succinate (HMPCAS). The methodical pathway is illustrated in Figure 1. EFV:polymer (1:4 w/w) mixtures of 1 g were prepared by ball milling in 25 mL stainless steel jars with two 12 mm stainless steel balls for 5 min at 30 Hz. EFV:polymer mixtures of 200 mg were then subjected to vacuum compression molding at 160-210 °C for 5 min, followed by 5-10 min of cooling. The resulting ASD discs (Ø: 20 mm) were ball milled in 5 mL stainless steel jars with two 5 mm stainless steel balls in cycles of 10-20 sec at 30 Hz followed by sieving (180-355 µm). Size 9 capsules loaded with 15-17 mg ASD or 3 mg crystalline EFV were then dosed to fasted rats, and blood samples collected from the tail vein. Blood plasma was isolated by centrifugation and EFV quantified by HPLC-UV. In parallel, capsules were tested in a PAMPA-membrane based microFLUX setup with or without the addition of a hydrophilic polyvinylidene fluoride (PVDF) membrane filter (0.45 µm) facing the donor side. The donor medium consisted of 14 mL HCl pH 3.5 for the initial 15 min before adjusting to 21 mL of phosphate buffer pH 7.0 with non-sink conditions maintained throughout the study. The receiver medium consisted of 1% w/w sodium lauryl sulfate in a pH 7.4 HEPES buffer.

Results: Applying the PAMPA-based microFLUX setup did not result in a rank order correlation between the AUC in the receiver medium and the AUC from the in vivo study (Figure 2A). However, adding the hydrophilic PVDF membrane filter on the donor side of the PAMPA membrane resulted in a linear correlation (R² = 0.94) between the in vitro and in vivo data (Figure 2B).

Conclusion: As expected, crystalline EFV was resulting in significantly lower plasma concentrations compared to the four ASD formulations, Yet, crystalline EFV was outperforming ASDs when applying the regular microFLUX setup, which might be explained by the difference in accessibility to the absorption membrane in vitro and in vivo. Mucus in the gastrointestinal tract will prevent close proximity between solid drug particles and the absorptive barrier. In contrast, solid drug particles might directly be exposed to the membrane in the regular PAMPA setup where a phospholipid solution in dodecane is added to a hydrophobic PVDF membrane. Thus, the physiological relevance of adding the hydrophilic PVDF membrane filter to the donor compartment can be regarded as a mucus-like mesh protecting the PAMPA membrane. In this study, the most pronounced effect was observed for crystalline EFV, which went from being the best in vitro performer to being the worst, thus establishing IVIVC. While none of the present ASDs showed a characteristic spring dissolution profile, this approach might likewise improve on the absorption predictability of formulations causing drug precipitation. Whether the approach can prove advantageous for more complex ASDs e.g. micelle-forming and/or tertiary systems including surfactants or even other formulation strategies e.g. lipid-based formulations is yet to be investigated.

References: 1. Newman A.; Knipp G. and Zografi G. Assessing the performance of amorphous solid dispersions, J. Pharm. Sci., 101, 1355-1377 (2012).
2. Schittny A.; Huwyler J. and Puchkov M. Mechanisms of increased bioavailability through amorphous solid dispersions: a review, Drug Deliv. 27, 110-127 (2020).

Acknowledgements: The animal experiments were carried out in accordance with the Danish law on animal experiments as approved by the Danish Animal Experiments Inspectorate in concordance with the EU directive 2010/63/EU under license no. 2019-15-0201-00262.


Figure 1. Schematic overview of the preparation steps of a gelatine capsule filled with an amorphous solid dispersion for in vitro and in vivo studies.


Figure 2. In vitro-in vivo correlation of four amorphous solid dispersions and crystalline efavirenz. A: In vitro data from the microFLUX setup with PAMPA membrane only. B: In vitro data from the microFLUX setup with an additional hydrophilic membrane. Data are presented as mean ± SEM.