Changing the physical state from crystalline to amorphous is an elegant method to increase the bioavailability of poorly soluble new chemical entity (NCE) drug candidates. Subsequently, we report findings from repeat-dose toxicity studies of an NCE formulated as a spray-dried amorphous solid dispersion (SD-ASD) based on hydroxypropyl methylcellulose acetate succinate (HPMC-AS) in rats. At necropsy, agglomerates of SD-ASD were found in the stomach and small intestine, which in reference to literature were termed pharmacobezoars. We interpreted the pH-dependent insolubility of HPMC-AS in the acidic gastric environment to be a precondition for pharmacobezoar formation. Gastric pharmacobezoars were not associated with clinical signs or alterations of clinical pathology parameters. Pharmacobezoar-correlated histopathological findings were limited to the stomach and consisted of atrophy, erosion, ulcer, and inflammation, predominantly of the nonglandular mucosa. Pharmacobezoars in the small intestines induced obstructive ileus with overt clinical signs which required unscheduled euthanasia, prominent alterations of clinical pathology parameters indicative of hypotonic dehydration, degenerative and inflammatory processes in the gastrointestinal tract, and secondary renal findings. The incidence of pharmacobezoars increased with dose and duration of dosing. Besides the relevance of pharmacobezoars to animal welfare, they limit the non-observed adverse effect level in nonclinical testing programs and conclusively their informative value.

The formation of pharmacobezoars from suspensions of spray-dried amorphous solid dispersions (SD-ASDs) of new chemical entities (NCEs) and hydroxypropyl methylcellulose acetate succinate (HPMC-AS) represents a non-compound related adverse effect in preclinical oral toxicity studies in rodents. Whereas the contribution of the insolubility of the carrier polymer to this process taking place in the acidic environment of the rodent stomach is conclusive, unawareness of the extent of in vivo pharmacobezoar formation is adverse. In order to evaluate the risk of pharmacobezoar formation before in vivo administration, we subsequently introduce an in vitro model to assess the agglomeration potential of solid dispersions. To verify that the pharmacobezoar formation potential can be assessed based on the observed agglomeration potential, we conducted a sequence of experiments with two HPMC-AS-based SD-ASD formulations. In vitro, we found their different in vivo pharmacobezoar formation potential reflected by a significantly increased agglomerated mass of formulation 1 per day compared to formulation 2. In order to find an approach to reduce the agglomeration potential of solid dispersion from suspensions, we further applied the model to investigate the impact of the viscosity of the vehicle used to prepare suspensions on agglomerate formation.

Spray-dried amorphous solid dispersions of new chemical entities and pH-dependent soluble polymer hydroxypropyl methylcellulose acetate succinate (HPMC-AS) were found to form solid agglomerates in the gastrointestinal tract of rodents after oral administration. These agglomerates, referring to descriptions of intra-gastrointestinal aggregated oral dosage forms termed pharmacobezoars, represent a potential risk for animal welfare. Previously, we introduced an in vitro model to assess the agglomeration potential of amorphous solid dispersions from suspensions and how it can be reduced. In this work, we investigated if the in vitro effective approach of viscosity enhancement of the vehicle used to prepare suspensions of amorphous solid dispersions could reduce the pharmacobezoar formation potential following repeated daily oral dosing to rats as well. The dose level of 2400 mg/kg/day used in the main study was determined in a dose finding study carried out in advance. In the dose finding study, MRI investigations were carried out at short time intervals to gain insights into the process of pharmacobezoar formation. Whereas MRI investigations underlined the importance of the forestomach for the formation of pharmacobezoars, viscosity enhancement of the vehicle reduced the incidence of pharmacobezoars, delayed the onset of pharmacobezoar formation and reduced the overall mass of pharmacobezoars found at necropsy.