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International Journal of Pharmaceutics
journal homepage: www.elsevier.com/locate/ijpharm
Flow-through cell-based in vitro release method for triamcinolone acetonide
poly (lactic-co-glycolic) acid microspheres
Namita P. Tipnis
a
, Jie Shen
a
, Derek Jackson
b
, Daniel Leblanc
b
, Diane J. Burgess
a,
⁎
a
Department of Pharmaceutical Sciences, University of Connecticut, Storrs, CT 06269, USA
b
Flexion Therapeutics, Burlington, MA 01803, USA
ARTICLE INFO
Keywords:
Polymeric microspheres
Triamcinolone acetonide
In vitro release testing
Flow-through cell apparatus
ABSTRACT
The main objective of the current research was to develop a compendial flow-through cell apparatus based in
vitro release testing method for sustained-release triamcinolone acetonide–loaded poly (lactic-co-glycolic) acid
(PLGA) microspheres. Media-based and instrument-based parameters, such as surfactant type, concentration,
media volume, flow rate, and testing temperature, were investigated. In addition, a detailed exploration was
performed to reveal polymer degradation encompassing pore formation, channeling, and triamcinolone acet-
onide release from microspheres using freeze-fracture scanning electron microscopy. The developed USP ap-
paratus 4 method demonstrated more than 85% drug release from the microspheres in 12 days and showcased
reproducibility between different microsphere batches. Large medium volume (15 times saturation solubility) at
low surfactant concentration was identified as a critical media-based parameter, with potential application in
testing of other sensitive poorly soluble drugs. At 35 °C, drug release via pore channeling to the surface was
evident, whereas at 39 °C, drug release slowed due to polymer plasticization. It was demonstrated here for the
first time that elevated temperature-accelerated testing does not work for all PLGA-based microsphere products.
1. Introduction
Biodegradable polymeric microspheres are complex particulate
systems that have been widely used for long-term controlled delivery of
both small molecules and macromolecules such as peptides and pro-
teins (Varde and Pack, 2004; Kim and Pack, 2006). Poly (lactic-co-
glycolic acid) (PLGA) is a biodegradable and biocompatible polymeric
vehicle used to achieve sustained delivery of loaded actives (Makadia
and Siegel, 2011; Anderson and Shive, 2012). PLGA polymers are one of
the most researched polymers for applications in controlled release
systems due to their easy-to-tune mechanical properties. They have
been widely used in several commercial US Food and Drug Adminis-
tration (FDA)–approved microsphere products, which release a range of
small molecule, peptide and protein drugs (Wang et al., 2012).
During the product development stage, it is critical to ensure con-
sistent product quality without altering in vivo product performance. In
vitro drug release testing is a powerful tool used during product de-
velopment in the pharmaceutical industry to ensure batch-to-batch
reproducibility and subsequent product quality and performance.
Currently, there are no compendial apparatus-based in vitro release
testing methods for formulations such as microspheres (Tipnis and
Burgess, 2017). However, the FDA has recommended using the United
States Pharmacopoeia (USP) apparatus 4 (flow-through cell) (Tipnis
and Burgess, 2017). The USP apparatus 4 was originally developed for
modified-release oral dosage forms and later adapted for in vitro release
testing of microspheres (Voisine et al., 2008). The USP apparatus 4
consists of a media reservoir, a pump, and a flow-through cell (Tipnis
and Burgess, 2017).
The in vitro release test can be run in both open- and closed-loop
configurations. In the open-loop configuration, media pass once
through the cell and then pass to a detector or are collected/discharged.
The open-loop configuration therefore requires high media volume. In
the closed-loop configuration, the media circulate through the cell
during the entire testing period, and samples are withdrawn from the
media reservoir at periodic intervals and replaced with fresh media.
Zolnik et al. (2006) have developed a modified USP apparatus 4 method
for microspheres, wherein glass beads and microspheres are mixed to-
gether in the flow-through cell to prevent microsphere aggregation and
https://doi.org/10.1016/j.ijpharm.2020.119130
Received 12 November 2019; Received in revised form 2 February 2020; Accepted 8 February 2020
Abbreviations: ACN, acetonitrile; DMSO, dimethyl sulfoxide; US FDA, United States Food and Drug Administration; GPC, gel permeation chromatography; PBS,
phosphate buffered solution; PLGA, poly (lactic-co-glycolic acid); SDS, sodium dodecyl sulfate; SEM, scanning electron microscopy; THF, tetrahydrofuran; USP,
United States Pharmacopeia
⁎
Corresponding author.
E-mail address: d.burgess@uconn.edu (D.J. Burgess).
International Journal of Pharmaceutics 579 (2020) 119130
Available online 16 February 2020
0378-5173/ © 2020 Elsevier B.V. All rights reserved.
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