A reproducible accelerated in vitro release testing method for PLGA microspheres

Abstract

The objective of the present study was to develop a discriminatory and reproducible accelerated in vitro release method for long-acting PLGA microspheres with inner structure/porosity differences. Risperidone was chosen as a model drug. Qualitatively and quantitatively equivalent PLGA microspheres with different inner structure/porosity were obtained using different manufacturing processes. Physicochemical properties as well as degradation profiles of the prepared microspheres were investigated. Furthermore, in vitro release testing of the prepared risperidone microspheres was performed using the most common in vitro release methods (i.e., sample-and-separate and flow through) for this type of product. The obtained compositionally equivalent risperidone microspheres had similar drug loading but different inner structure/porosity. When microsphere particle size appeared similar, porous risperidone microspheres showed faster microsphere degradation and drug release compared with less porous microspheres. Both in vitro release methods investigated were able to differentiate risperidone microsphere formulations with differences in porosity under real-time (37 °C) and accelerated (45 °C) testing conditions. Notably, only the accelerated USP apparatus 4 method showed good reproducibility for highly porous risperidone microspheres. These results indicated that the accelerated USP apparatus 4 method is an appropriate fast quality control tool for long-acting PLGA microspheres (even with porous structures).

Keywords: Accelerated in vitro release; Compositionally equivalent; PLGA microspheres; Porous; Risperidone; USP apparatus 4.

Fig. 1

Changes in molecular weight of PLGA of blank (A) and risperidone loaded PLGA microspheres (B) after exposure to 10 mM PBS (pH 7.4) at 37°C.

Fig. 2

SEM micrographs of Formulation 1 (A–F) and Formulation 2 (G–L) after exposure to 10 mM PBS (pH 7.4) over a period of 35 days. Symbol: blue arrows point to indentations on the surface of the microspheres; red arrows point to pores on the surface of the microspheres.

Fig. 3

In vitro release profiles of the compositionally equivalent risperidone microspheres with manufacturing differences obtained using different release testing methods at 37°C in 10 mM PBS (pH 7.4) (n=3).

Fig. 4

In vitro release profiles of the compositionally equivalent risperidone microspheres with manufacturing differences using (A) the sample-and-separate and (B) USP apparatus 4 methods at 45°C in 10 mM PBS (pH 7.4) (n=3).

Fig. 5

In vitro release profiles of the prepared risperidone microspheres in 10 mM PBS (pH 7.4) at 37°C (time-scaled) and at 45°C using different release testing methods (n=3). (A) Formulation 1 and (B) Formulation 2 using the sample-and-separate method. (C) Formulation 1 and (D) Formulation 2 using the USP apparatus 4 method. Insert figures show linear correlations between real-time (time-scaled) (37°C) and accelerated (45°C) fraction risperidone released.

Fig. 5

In vitro release profiles of the prepared risperidone microspheres in 10 mM PBS (pH 7.4) at 37°C (time-scaled) and at 45°C using different release testing methods (n=3). (A) Formulation 1 and (B) Formulation 2 using the sample-and-separate method. (C) Formulation 1 and (D) Formulation 2 using the USP apparatus 4 method. Insert figures show linear correlations between real-time (time-scaled) (37°C) and accelerated (45°C) fraction risperidone released.

Fig. 6

In vitro release profiles of the prepared risperidone microspheres (Formulation 1 (A) and Formulation 2 (B)) in 10 mM PBS (pH 7.4) using the sample-and-separate method at 45°C (n=3).

Fig. 7

In vitro release profiles of the prepared risperidone microspheres (Formulation 1 (A) and Formulation 2 (B)) in 10 mM PBS (pH 7.4) using the USP apparatus 4 method at 45°C (n=3).

Fig. 8

(A) In vitro release profiles of Formulation 3 in 10 mM PBS (pH 7.4) at 37°C (time-scaled) and at 45°C using the USP apparatus 4 method (n=3). Insert figure shows the linear correlation between real-time (time-scaled) (37°C) and accelerated (45°C) fraction risperidone released. (B) In vitro release profiles of Formulations 2 and 3 in 10 mM PBS (pH 7.4) using the USP apparatus 4 method at 45°C (n=3).