(W0930-07-40) In Vivo Evaluation of Bexarotene Oral Microparticles in Beagle Dogs

Purpose: Microparticles – which consist of an active pharmaceutical ingredient (API) and a polymer – have been widely studied for decades as an attractive formulation technology for controlled and extended drug release [1]. They are mostly developed as parenteral formulations. The API is encapsulated inside the polymer matrix. After administration, the polymer either dissolves or degrades in the human body and releases the API [2]. In this study an emulsion-based process was used for preparing microparticles to leverage the several advantages of the process to produce amorphous solid dispersions (ASD) for solubility enhancement [3]. Those advantages comprise the creation of uniform particle-engineered particles with a controlled target particle size at high yield and the free flowability of the resulting ASDs. The prepared bexarotene microparticles were analyzed regarding their particle size, physical state of the drug in the ASD, the in vitro dissolution performance and in their in vivo pharmacokinetic performance in comparison to a spray drying process and a marketed drug product.

Methods: Preparation of bexarotene ASD oral microparticles: EUDRAGIT® E PO, EUDRAGIT® RL PO (Evonik Industries AG, Germany) and bexarotene were dissolved in dichloromethane in a ratio of 100:300:33.3 (bexarotene:polymer1:polymer2), representing the dispersed phase (DP). Poly vinyl alcohol (Mowiol 4-88, Sigma, Germany) was dissolved in deionized water which was used as continuous phase (CP). The CP and DP solutions were mixed to generate an emulsion using a static mixer. After mixing the solid wet particles were separated from the aqueous phase and dried. Spray dried bexarotene oral microparticles were prepared with a ProCepT spray dryer (4M8-TriX, ProCepT, Zelzate, Belgium). In vitro dissolution study: Dissolution experiments were conducted in triplicate with 75 mg bexarotene drug substance or an equivalent amount of ASD using USP apparatus II from ERWEKA GmbH (Langen, Germany). The paddle speed was set to 150 rpm. All experiments were performed first in 700 mL of 0.1N HCl for 15 min. Afterwards, a buffer conversion took place to pH 6.8 (Ph. Eur.) with a final volume of 914 mL. All dissolution experiments were performed at 37 ± 0.5 °C. The test duration in the buffered stage was 165 min. All samples were withdrawn by a fraction collector and manually diluted 1:1 (v/v) with methanol, before HPLC analysis. In vivo study design: To investigate the performance of the prepared oral bexarotene ASD microparticles, two processes (spray-drying and emulsion-based approach) were compared to a marketed product and the drug substance bexarotene in an in vivo beagle dog pharmacokinetic study. Each animal (n=6) received 75 mg of bexarotene or an equivalent amount of ASD. Male beagle dogs (n=6) were dosed for a single occasion by oral gavage with EBP‑100‑300‑33.3 (prepared via an emulsion-based approach), SDG‑100‑300‑33.3 (prepared via spray drying) or bexarotene drug substance formulated as microparticle dispersions in Elix® water. In the last period, the animals were dosed with a marketed bexarotene product (ready to use softgel capsule). At 20 minutes before and 30 minutes after dosing, the animals received a 6 µg/kg intramuscular pentagastrin injection to promote acid secretion in the canine stomach and eventually reaching gastric pH conditions similar to fastened humans. A wash-out of 3 to 4 days between the dose periods were applied. Following each dosing, blood samples (~0.5 mL) were collected from animals in all periods at pre-dose and at 0.5, 1, 2, 4, 6, 8, 12, 24 and 48 hours post-dose by sampling from the jugular vein.

Results: With the emulsion-based process uniform round microparticles with a mean particle size of 163 µm (d50) and a smooth surface could be prepared (data not shown). Furthermore, the crystalline bexarotene was transferred by both processes, emulsion-based and spray-dried, respectively, into an amorphous physical state determined via XRPD (data not shown). As shown in Figure 1, the in vitro dissolution profiles showed no solubility of the bexarotene drug substance and a neglectable increase with the physical mixture of the formulation components. In comparison to the marketed bexarotene softgel capsule (~7%), bexarotene ASD microparticles increased the dissolution rate up to 62%. Afterwards, four bexarotene formulations were benchmarked in an intrinsic pharmacokinetic in vivo study with male beagle dogs (Figure 2). Following a single oral administration of the formulation, amorphous solid dispersion prepared via the emulsion-based process (EBP-100-300-33.3) showed superior pharmacokinetic performance in comparison to the well-established spray-drying process, even if the formulation components were kept the same. Moreover, the marketed softgel capsule disclosed a lower AUC value than the spray-dried formulation.

Conclusion: This study has illustrated that oral microparticles offer a unique solution to solubility enhancement when it comes to the formulation of challenging APIs, overcoming processing hurdles and optimizing pharmacokinetic performance. The new process facilitates the solubilization of highly challenging compounds, creates free-flowing powder through lean process with advanced particle-engineering control and leverages the full therapeutic potential of an API.

References: [1] W. Li et al., Clinical translation of long-acting drug delivery formulations, Nature Review Materials, 2022

[2] S. Freitas et al., Microencapsulation by Solvent Extraction/Evaporation: Reviewing the State of the Art of Microsphere Preparation Process Technology, Journal of Controlled Release 102(2):313-32, 2005

[3] S. Huang & R.O. Williams 3rd, Review Article: Effects of the Preparation Process on the Properties of Amorphous Solid Dispersions, AAPS PharmSciTech 2017


Figure 1: In vitro dissolution profiles of bexarotene drug substance, a physical mixture consisting of bexarotene, Eudragit® E PO and Eudragit® RL PO, bexarotene ASD microparticles and marketed bexarotene softgel capsule.


Figure 2: Summary of bexarotene pharmacokinetic parameters in male beagle dog plasma, following single oral administration. EBP-100-300-33.3 represents the ASD microparticles prepared via the emulsion-based process. SDG-100-300-33.3 represents the ASD microparticles prepared via the spray-dried process. Bexarotene is the crystalline drug substance. Each value designates the mean value (n=6).