Scanning Analysis of Sequential Semisolvent Vapor Impact To Study Naltrexone Release from Poly(lactide-co-glycolide) Microparticles.

Poly(lactide-co-glycolide) (PLGA)-based microparticle formulations have been a mainstay of long-acting injectable drug delivery applications for decades. Despite a long history of use, tools and techniques to analyze and understand these formulations are still under development. Recently, a new characterization method was introduced known as the surface analysis after sequential semisolvent impact using sequential semisolvent vapors. The vapor-based technique is named, for convenience, surface analysis of (semisolvent) vapor impact (SAVI). In the SAVI method, discretely controlled quantities of selected organic semisolvents in the vapor phase were applied to PLGA microparticles to track particle morphological changes by laser scanning confocal microscopy. Subsequently, the morphological images were analyzed to calculate mean peak height (Sa), core height (Sk), kurtosis (Sku), dale void volume (Vvv), the density of peaks (Spd), maximum height (Hm), and the shape ratio (Rs). Here, the SAVI method was applied to naltrexone-loaded microparticles manufactured internally and Vivitrol, a commercial formulation. SAVI analysis of these microparticles indicated that the two primary mechanisms controlling the naltrexone release were the formation of discrete, self-crystallized portions of naltrexone within the PLGA structure and the degradation of PLGA chains through nucleophilic substitution. The relatively higher amounts of naltrexone crystals resulted in prolonged release than lower amounts of crystals. Data from gel permeation chromatography, differential scanning calorimetry, and in vitro release measurements all point to the importance of naltrexone crystal formation. This study highlights the utility of SAVI for gaining further insights into the microstructure of PLGA formulations and using SAVI data to support research, product development, and quality control applications for microparticle formulations of pharmaceuticals.

Surface analysis of sequential semi-solvent vapor impact (SAVI) for studying microstructural arrangements of poly(lactide-co-glycolide) microparticles.

Biodegradable poly(lactide-co-glycolide) (PLGA) microparticles have been used as long-acting injectable (LAI) drug delivery systems for more than three decades. Despite extensive use, few tools have been available to examine and compare the three-dimensional (3D) structures of microparticles prepared using different compositions and processing parameters, all collectively affecting drug release kinetics. Surface analysis after sequential semi-solvent impact (SASSI) was conducted by exposing PLGA microparticles to different semi-solvent in the liquid phase. The use of semi-solvent liquids presented practical experimental difficulties, particularly in observing the same microparticles before and after exposure to semi-solvents. The difficulties were overcome by using a new sequential semi-solvent vapor (SSV) method to examine the morphological changes of the same microparticles. The SASSI method based on SSV is called surface analysis of semi-solvent vapor impact (SAVI). Semi-solvents are the solvents that dissolve PLGA polymers depending on the polymer's lactide:glycolide (L:G) ratio. A sequence of semi-solvents was used to dissolve portions of PLGA microparticles in an L:G ratio-dependent manner, thus revealing different structures depending on how microparticles were prepared. Exposing PLGA microparticles to semi-solvents in the vapor phase demonstrated significant advantages over using semi-solvents in the liquid phase, such as in control of exposure conditions, access to imaging, decreasing the time for sequential exposure of semi-solvents, and using the same microparticles. The SSV approach for morphological analysis provides another tool to enhance our understanding of the microstructural arrangement of PLGA polymers. It will improve our comprehensive understanding of the factors controlling drug release from LAI formulations based on PLGA polymers.

Analysis of semi-solvent effects for PLGA polymers.

Poly(lactide-co-glycolide) polymers (PLGAs) have been used in many clinical formulations of injectable, long-acting formulations. Frequently, PLGAs having different lactide:glycolide (L:G) ratios, molecular weights (MWs), end-groups, and molecular structures have been used individually or in mixtures. To understand the properties of existing formulations made of PLGAs and to develop new formulations, understanding PLGA properties is essential. Yet, the separation of individual PLGA components from a mixture and their characterization has been challenging due to an incomplete understanding of PLGAs. This study focuses on separating PLGAs based on their molecular properties, such as L:G ratio, molecular weight, and comonomer sequence. The separation of PLGAs exploits the use of semi-solvents that dissolve only PLGAs having lactide contents (L%) above a certain threshold. More semi-solvents have been identified that show a specific transition L% between 50 and 100%. The mechanism study of semi-solvents indicates that semi-solvents, in general, prefer PLGAs with relatively higher L%, lower molecular weight, and higher G-L sequences as opposed to G-G sequences. The examination of a series of esters and ketones indicates that a solvent with lower molar volume is more effective as a semi-solvent. At a similar molar volume, esters are more effective than ketones in dissolving PLGAs with the same L:G ratio. The ability to separate and identify PLGA fractions allows better characterization of existing formulations and higher flexibility in designing new injectable, long-acting PLGA formulations.

Potential Roles of the Glass Transition Temperature of PLGA Microparticles in Drug Release Kinetics.

Poly(lactic-co-glycolic acid) (PLGA) has been used for long-acting injectable drug delivery systems for more than 30 years. The factors affecting the properties of PLGA formulations are still not clearly understood. The drug release kinetics of PLGA microparticles are influenced by many parameters associated with the formulation composition, manufacturing process, and post-treatments. Since the drug release kinetics have not been explainable using the measurable properties, formulating PLGA microparticles with desired drug release kinetics has been extremely difficult. Of the various properties, the glass transition temperature, Tg, of PLGA formulations is able to explain various aspects of drug release kinetics. This allows examination of parameters that affect the Tg of PLGA formulations, and thus, affecting the drug release kinetics. The impacts of the terminal sterilization on the Tg and drug release kinetics were also examined. The analysis of drug release kinetics in relation to the Tg of PLGA formulations provides a basis for further understanding of the factors controlling drug release.

Formulation composition, manufacturing process, and characterization of poly(lactide-co-glycolide) microparticles.

Injectable long-acting formulations, specifically poly(lactide-co-glycolide) (PLGA) based systems, have been used to deliver drugs systemically for up to 6 months. Despite the benefits of using this type of long-acting formulations, the development of clinical products and the generic versions of existing formulations has been slow. Only about two dozen formulations have been approved by the U.S. Food and Drug Administration during the last 30 years. Furthermore, less than a dozen small molecules have been incorporated and approved for clinical use in PLGA-based formulations. The limited number of clinically used products is mainly due to the incomplete understanding of PLGA polymers and the various variables involved in the composition and manufacturing process. Numerous process parameters affect the formulation properties, and their intricate interactions have been difficult to decipher. Thus, it is necessary to identify all the factors affecting the final formulation properties and determine the main contributors to enable control of each factor independently. The composition of the formulation and the manufacturing processes determine the essential property of each formulation, i.e., in vivo drug release kinetics leading to their respective pharmacokinetic profiles. Since the pharmacokinetic profiles can be correlated with in vitro release kinetics, proper in vitro characterization is critical for both batch-to-batch quality control and scale-up production. In addition to in vitro release kinetics, other in vitro characterization is essential for ensuring that the desired formulation is produced, resulting in an expected pharmacokinetic profile. This article reviews the effects of a selected number of parameters in the formulation composition, manufacturing process, and characterization of microparticle systems. In particular, the emphasis is focused on the characterization of surface morphology of PLGA microparticles, as it is a manifestation of the formulation composition and the manufacturing process. Also, the implication of the surface morphology on the drug release kinetics is examined. The information described here can also be applied to in situ forming implants and solid implants.

Method matters: Development of characterization techniques for branched and glucose-poly(lactide-co-glycolide) polymers.

Defining the qualitative sameness of parenteral formulations comprised of poly(lactide-co-glycolide) (PLGA) requires assays of the relevant properties of polymer from each formulation. Gel-permeation chromatography with quaternary detection (GPC-4D) has been previously applied to other polymers, and the relevant mathematical parameters for their characterization are available; however, such parameters have not been described for branched PLGA polymers. Little information is available for the determination of glucose within glucose-PLGA (Glu-PLGA) branched polymers. This study describes the experimental methods of defining the mathematical parameters for characterization of branched PLGA polymers and the validation of these parameters using known branched-PLGA standards. The glucose, used as an initiator, was tracked through the synthesis of Glu-PLGA by both 13C NMR and enzymatic analysis. The analytical determination of the relevant parameters defining Glu-PLGA, such as the branching number, and the presence of glucose, requires the use of appropriate procedures experimentally validated in a systematic manner. The procedures described in this study were developed for characterization of Glu-PLGA with the lactide:glycolide (L:G) ratio of 55:45 used in Sandostatin® LAR. The procedures can also be used for characterization of Glu-PLGAs made of different L:G ratios.

Injectable, long-acting PLGA formulations: Analyzing PLGA and understanding microparticle formation.

Injectable, long-acting depot formulations based on poly(lactide-co-glycolide) (PLGA) have been used clinically since 1989. Despite 30 years of development, however, there are only 19 different drugs in PLGA formulations approved by the U.S. Food and Drug Administration (FDA). The difficulty in developing depot formulations stems in large part from the lack of a clear molecular understanding of PLGA polymers and a mechanistic understanding of PLGA microparticles formation. The difficulty is readily apparent by the absence of approved PLGA-based generic products, limiting access to affordable medicines to all patients. PLGA has been traditionally characterized by its molecular weight, lactide:glycolide (L:G) ratio, and end group. Characterization of non-linear PLGA, such as star-shaped glucose-PLGA, has been difficult due to the shortcomings in analytical methods typically used for PLGA. In addition, separation of a mixture of different PLGAs has not been previously identified, especially when only their L:G ratios are different while the molecular weights are the same. New analytical methods were developed to determine the branch number of star-shaped PLGAs, and to separate PLGAs based on L:G ratios regardless of the molecular weight. A deeper understanding of complex PLGA formulations can be achieved with these new characterization methods. Such methods are important for further development of not only PLGA depot formulations with controllable drug release kinetics, but also generic formulations of current brand-name products.

Characterization of branched poly(lactide-co-glycolide) polymers used in injectable, long-acting formulations.

Poly(lactide-co-glycolide) (PLGA) has been used in many injectable, long-acting depot formulations. Despite frequent use of PLGA, however, its characterization has been limited to measuring its molecular weight, lactide:glycolide (L:G) ratio, and end-group. These conventional methods are not adequate for characterization of unique PLGA polymers, such as branched PLGA. Glucose-initiated PLGA (Glu-PLGA) has been used in Sandostatin® LAR Depot (octreotide acetate for injectable suspension) approved by the U.S. Food and Drug Administration (FDA) in 1998. Glu-PLGA is a branched (also known as star-shaped) polymer and determining its properties has been challenging. It is necessary to develop methods that can determine and characterize the branching parameters of Glu-PLGA. Such characterization is important not only for the quality control of formulations, but also for developing generic parenteral formulations that are required to have the same excipients in the same amount (qualitative/quantitative (Q1/Q2) sameness) as their Reference Listed Drug (RLD). In this study, an analytical technique was developed and validated using a series of branched-PLGA standards, and it was used to determine the branching parameters of Glu-PLGA extracted from Sandostatin LAR, as well as Glu-PLGAs obtained from three different manufacturers. The analytical technique was based on gel-permeation-chromatography with quadruple detection systems (GPC-4D). GPC-4D enabled characterization of Glu-PLGA in its concentration, absolute molecular weight, hydrodynamic radius and intrinsic viscosity. The plot of the branch units per molecule as a function of molar mass provides a unique profile of each branched PLGA. The Mark-Houwink plots were also used to distinguish different Glu-PLGAs. These ensemble identification methods indicate that the branch units of Glu-PLGAs extracted from Sandostatin LAR range from 2 (i.e., linear) at the lower end of the molecular weight to <4 for the majority (94%) of Glu-PLGA.

Complex sameness: Separation of mixed poly(lactide-co-glycolide)s based on the lactide:glycolide ratio.

Poly (lactide-co-glycolide) (PLGA) has been used for making injectable, long-acting depot formulations for the last three decades. An in depth understanding of PLGA polymers is critical for development of depot formulations as their properties control drug release kinetics. To date, about 20 PLGA-based formulations have been approved by the U.S. Food and Drug Administration (FDA) through new drug applications, and none of them have generic counterparts on the market yet. The lack of generic PLGA products is partly due to difficulties in reverse engineering. A generic injectable PLGA product is required to establish qualitative and quantitative (Q1/Q2) sameness of PLGA to that of a reference listed drug (RLD) to obtain an approval from the FDA. Conventional characterizations of PLGA used in a formulation rely on measuring the molecular weight by gel permeation chromatography (GPC) based on polystyrene molecular weight standards, and determining the lactide:glycolide (L: G) ratio by 1H NMR and the end-group by 13C NMR. These approaches, however, may not be suitable or sufficient, if a formulation has more than one type of PLGA, especially when they have similar molecular weights, but different L:G ratios. Accordingly, there is a need to develop new assay methods for separating PLGAs possessing different L:G ratios when used in a drug product and characterizing individual PLGAs. The current work identifies a series of semi-solvents which exhibit varying degrees of PLGA solubility depending on the L:G ratio of the polymer. A good solvent dissolves PLGAs with all L:G ratios ranging from 50:50 to 100:0. A semi-solvent dissolves PLGAs with only certain L:G ratios. Almost all semi-solvents identified in this study increase their PLGA solubility as the L:G ratio increases, i.e., the lactide content increases. This lacto-selectivity, favoring higher L:G ratios, has been applied for separating individual PLGAs in a given depot formulation, leading to analysis of each type of PLGA. This semi-solvent method allows a simple, practical bench-top separation of PLGAs of varying L:G ratios. This method enables isolation and identification of individual PLGAs from a complex mixture that is critical for the quality control of PLGA formulations, as well as reverse engineering for generic products to establish the Q1/Q2 sameness.

Beyond Q1/Q2: The Impact of Manufacturing Conditions and Test Methods on Drug Release From PLGA-Based Microparticle Depot Formulations.

Drug-loaded polymeric microparticles have been used as long-acting injectable (LAI) depot formulations. To obtain U.S. Food and Drug Administration approval, a generic LAI depot product needs to be qualitatively (Q1) and quantitatively (Q2) the same in terms of inactive ingredients as its reference-listed drug. However, Q1/Q2 sameness as the reference-listed drug does not guarantee the same in vitro drug release profile and in vivo performance, especially when the manufacturing methods are different. There is little consensus on how the in vitro testing needs to be done to examine the release profiles of LAI depot formulations. This study examined the manufacturing differences in making risperidone-loaded poly(lactide-co-glycolide) microparticles and their impact on the release kinetics. It also examined the impacts of in vitro testing methods on the drug release profiles. Two in-house manufactured risperidone poly(lactide-co-glycolide) microparticles and Risperdal Consta® were used in the study. Of the in vitro release methods tested, the orbital agitation method provided the most reproducible release profiles. The results indicate that the in vitro release kinetics depend not only on manufacturing procedures but also on the in vitro testing conditions, such as the agitation speed, vessel-dimensions, solid beads, media exchange volume, and other parameters both under real-time and accelerated testing conditions. In the current case, the in vitro experimental condition seemed to affect the drug release kinetics more than the manufacturing differences. The developed orbital agitation release testing method is simple, robust, and reproducible, which allows the comparison of in vitro release profiles of formulations that are prepared with manufacturing differences.

A protocol for assay of poly(lactide-co-glycolide) in clinical products.

Poly(lactide-co-glycolide) (PLGA) is the key component of long acting drug products responsible for providing sustained release in a controlled manner. The objective of the current study was to develop and validate an analytical protocol to determine key properties of PLGA used in commercial long-acting drug products. Procedures to isolate PLGA from commercial products have been established and the key properties of PLGA, such as polymer molecular weight, lactide:glycolide (L:G) ratio, and nature of polymer end-cap, have been determined. Identification of the polymer end-cap was confirmed by using two PLGA polymers with acid and ester end-caps. Trelstar(®) and Risperdal Consta(®) were chosen as model products. The calculated L:G ratios of PLGA used in Trelstar(®) and Risperdal(®) are 52:48 and 78:22, respectively. PLGAs from both Trelstar(®) and Risperdal Consta(®) possess ester end-caps. Since the properties of specific PLGA in clinically used formulations are not readily available, this protocol will be useful in developing PLGA-based long acting drug products.