(W1030-07-38) Preparation and Pharmacokinetic Evaluation of Long-Acting Injectable Nanocrystalline Suspension of Montelukast

Purpose: Montelukast (MTK), a representative leukotriene receptor antagonist, is currently being emerged as a potential candidate for treating Alzheimer's disease. Long-acting injectable (LAI) delivery system could be recommended formulations for potent and effective dosing in elderly patients, with improved medication adherence with reduced dosage frequency. The goal of this study is to design a nanocrystalline suspension (NS)-based MTK LAI system and evaluate its pharmacokinetics profile and local tolerability following subcutaneous administration.

Methods: The amorphous MTK powder was converted into a crystalline form using a solution-mediated transformation procedure to decrease solubility and enhance the thermodynamic stability. Next, MTK-loaded crystalline suspensions were fabricated by pulverizing the drug powder into fine particles in an aqueous vehicle using a lab-scale bead-milling technique. 100 mg of MTK and 1 g of zirconia beads (0.3 mm) were added to the aqueous vehicle with the suspending agent. Scanning electron microscopy, X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), dynamic light scattering (DLS) was used to study the physicochemical properties of the formulations. The in vitro MTK dissolution profile from crystalline suspensions was comparatively evaluated using a shaking dissolution tester with the sample and separate method. To investigate in vivo PK behaviors, and histological analysis for local tolerability, micro and nanosized nanocrystalline suspensions were administered subcutaenously using a 31 G insulin syringe (30 mg/kg as MTK). The level of MTK in plasma was determined by HPLC mass spectroscopy (MS/MS) and PK parameters was calculated using PK analysis program. In vivo histological observation was performed by using paraffin technique with H&E staining and analyzed quantitatively.

Results: Microscopic and physical characterization revealed that the amorphous MTK powder was lucratively transformed into a crystalline form in acidic media (Fig. 1.). MTK crystalline suspensions were uniformly formulated into nanocrystals and microcrystals, with no alternation in crystalline form through the bead-milling process, with analogous crystallinity (melting point, 150°C). In vitro release test, size-dependent dissolution profiles was shown. In vivo PK parameters of micro and nanosized drug showed different results in initial half-life (Table 1). MTK NSs with particle sizes of 200 nm and 500 nm provided a protracted pharmacokinetics profile for up to 4 weeks in rats, with a higher maximum drug concentration in plasma than the 3 μm-sized injectable suspensions. Histopathological examination revealed that MTK NS caused chronic granulomatous inflammation at the injection site, which resolved after 4 weeks. In this study, the infiltration density of inflammatory cells was comparable between the groups, with no marked differences depending on the particle size.

Conclusion: Amorphous MTK powder was effectively converted into a crystalline form through solvent-mediated transformation. Subsequently, 200, 500, and 3,000 nm-sized MTK crystalline suspensions with distinctive crystalline forms were prepared using the lab-scale bead milling method. The prepared nanoformulations lasts a 4 weeks following a single SC injection. Moreover, histopathological observations showed that granulomatous inflammation caused by the MTK nanocrystal injection was transient and recoverable after 4 weeks, regardless of particle size. Therefore, the novel MTK LAI system is expected to be a potent tool for improving adherence in patients with Alzheimer's disease.

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Acknowledgments: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2022R1C1C1004561).

Figure 1. Morphological observation of MTK raw materials. SEM images of MTK raw materials (A) before and (B) after crystallization. Polarized images of the raw materials (C) before and (D) after crystallization.



Figure 2. Morphological and physical characteristics of MTK crystalline suspensions with different particle sizes. SEM images of (A) 200NS and (B) 500NS. Representative (C) XRD patterns and (D) DSC curves of (a) crystallized MTK raw material, (b) vehicle (acetate buffer solution with P80), (c) 200NS (c), (d) 500NS, and (e) 3MS



Figure 3. Plasma concentration-time profiles of MTK following SC injection of MTK crystalline suspensions with different particle sizes; 200NS (o), 500NS (●), and 3MS (■) in rats.