Freeze-drying using vacuum-induced surface freezing

A method of freezing during freeze-drying, which avoids undercooling of a solution and allows growth of large, dendritic ice crystals, was investigated. Aqueous solutions of mannitol, sucrose, or glycine were placed under a chamber vacuum of approximately 1 mbar at a shelf temperature of +10 degrees C. Under these conditions, the solutions exhibit surface freezing to form an ice layer of approximately 1-3 mm thickness. On releasing the vacuum and lowering the shelf temperature to below the freezing point of the ice in the solution, crystal growth occurs to yield large, chimney-like ice crystals. The duration of primary drying of a frozen cake--as measured by using inverse comparative pressure measurement--was up to 20% shorter than when using a "moderate" freezing procedure (2 K shelf temperature per min). With mannitol, however, the residual moisture content of the final dried product was higher than with moderate freezing, and with sucrose and glycine there was no difference. These findings are related to the structures of the dried cakes formed during freezing, as examined by light microscopy and wide-angle X-ray diffraction. The introduction of an annealing step (4 h at a shelf temperature slightly above the onset melting point of the ice in the frozen cake) combined with the vacuum-induced surface freezing procedure maintains the rapid primary drying and produces a low residual moisture (0.2%) for the freeze-dried mannitol solution.     

Effect of stopper processing conditions on moisture content and ramifications for lyophilized products: comparison of "low" and "high" moisture uptake stoppers

The purpose of this study was to evaluate the effect of processing and storage on the moisture content of two commercially available, 13-mm lyophilization stoppers designated as low moisture (LM) and high moisture (HM) uptake stoppers. The stopper moisture studies included the effect of steam sterilization time, drying time and temperature, equilibrium moisture content, lyophilization and moisture transfer from stopper to a model-lactose lyophilized cake. Results indicated that both stoppers absorbed significant amounts of moisture during sterilization and that the HM stopper absorbed significantly more water than the LM stopper. LM and HM stoppers required approximately 2 and 8 h drying at 105 degrees C, respectively, to achieve final moisture content of not more than 0.5 mg/stopper. Following drying, stopper moisture levels equilibrated rapidly to ambient storage conditions. The apparent equilibrium moisture level was approximately 7 times higher in the HM versus LM stopper. Freeze-drying had minimal effect on the moisture content of dried stoppers. Finally, moisture transfer from the stopper to the lyophilized product is dependent on the initial stopper water content and storage temperature. To better quantify the ramifications of stopper moisture, projections of moisture uptake over the shelf life of a drug product were calculated based on the product-contact surface area of stoppers. Attention to stopper storage conditions prior to use, in addition to processing steps, are necessary to minimize stability issues especially in low-fill, mass lyophilized products.     

Headspace Moisture Mapping and the Information That Can Be Gained about Freeze-Dried Materials and Processes

Regulatory authorities require proof that lyophilization (freeze drying) cycles have been developed logically and demonstrate uniformity. One measure of uniformity can be consistency of residual water content throughout a batch. In primary drying, heat transfer is effected by gaseous convection and conduction as well as the degree of shelf contact and evenness of heat applied; therefore residual water can be affected by container location, degree of container/tray/shelf contact, radiative heating, packing density, product formulation, and the cycle conditions themselves. In this study we have used frequency modulation spectroscopy (FMS) to create a map of headspace moisture (HSM) for 100% of vials within a number of freeze-dried batches. Karl Fischer (KF)/HSM correlations were investigated in parallel with the moisture mapping studies. A clear, linear relationship was observed between HSM and KF values for vials containing freeze-dried sucrose, implying a relatively straightforward interaction between water and the lyophilized cake for this material. Mannitol demonstrated a more complex correlation, with the interaction of different crystalline forms giving important information on the uniformity of the material produced. It was observed that annealing had a significant impact on the importance of heat transfer by conduction for vials in direct and non-direct contact with the shelf. Moisture mapping of all vials within the freeze dryer enabled further information to be obtained on the relationship of the formulation, process conditions, and equipment geometry on the intra-batch variability in HSM level. The ability of FMS to allow 100% inspection could mean that this method could play an important part in process validation and quality assurance. LAY ABSTRACT: Lyophilization, also known as freeze drying, is a relatively old technique that has been used in its most basic form for thousands of years (e.g., preservation of fish and meat products). In its more advanced form it is used to preserve many medical products; for example, many vaccines are not stable in solution and therefore need to be dried to allow long-term storage. In order to produce a freeze-dried vaccine, a complex understanding of the processes and critical temperatures is required. Once these have been understood, the material is dried to give relatively low moisture content (e.g., 2% w/w.) This low moisture content is critical for the long-term stability of the product, allowing doctors/chemists to store these goods on site for use when required. This research paper provides further information on a technique called frequency modulation spectroscopy (FMS) that has been used to map the moisture variation across samples within a freeze dryer, enabling us to increase our understanding of the role various processing conditions play on the relationship between the product and water. It has demonstrated its potential application for 100% batch monitoring and the validation of a system or assessment of changes made. This method could assist in improving quality assurance and ultimately the final product that reaches the consumer.     

Freeze-Drying From Organic Co-Solvent Systems,Part 2: Process Modifications to Reduce Residual Solvent Levels and Improve Product Quality Attributes

The use of co-solvent systems can benefit the freeze-drying process and product performance. In this study, cycle designs were applied based on existing recommendations for water-based formulations. Modifications thereof and the influence on the process (e.g., drying times) and product quality attributes (e.g., product appearance, residual solvent) were tested for various cosolvent systems. It was found that fast freezing was associated with the formation of large crystals for 50 mg/g polyvinylpyrrolidone in 40% 1,4-dioxane (w/w), resulting in a 7% reduction of primary drying. The application of high shelf temperatures during primary drying for 50 mg/g polyvinylpyrrolidone in 70% tert-butanol was feasible, resulting in shorter primary drying times but high residual solvent levels (7.7%). Most notable was that the inclusion of an evaporation step after freezing improved the product appearance for low-melting co-solvents (10% ethanol and 10% acetone). No ice or solvent nucleation occurred in the case of 50 mg/g mannitol in 50% N,N-dimethylacetamide during the normal freezing stage. Instead, the solution viscosity significantly increased after cooling to low shelf temperatures, followed by product evaporation (rather than sublimation) during the drying phase and failure to form a product cake after drying. The application of annealing enabled nucleation and sublimation.     

Characterization of Murine Monoclonal Antibody to Tumor Necrosis Factor (TNF-MAb) Formulation for Freeze-Drying Cycle Development

Purpose. This study was designed to characterize the formulation of protein pharmaceuticals for freeze-drying cycle development. Thermal properties of a protein formulation in a freezing temperature range are important in the development of freezing and primary drying phases. Moisture sorption properties and the relationship between moisture and stability are the bases for the design of the secondary drying phase. Methods. We have characterized the formulation of TNF-MAb for the purpose of freeze-drying cycle development. The methods include: DTA with ER probes, freeze-drying microscopy, isothermal water adsorption, and moisture optimization.Results. The DTA/ER work demonstrated the tendency to noneutectic freezing for the TNF-MAb formulation at cooling rates of –1 to –3°C/min. The probability of glycine crystallization during freezing was quite low. A special treatment, either a high subzero temperature holding or annealing could promote the maximum crystallization of glycine, which could dramatically increase the T_g' of the remaining solution. The freeze-drying microscopy further indicated that, after the product was annealed, the cake structure was fully maintained at a T_p below –25°C during primary drying. The moisture optimization study demonstrated that a drier TNF-MAb product had better stability. Conclusions. An annealing treatment should be implemented in the freezing phase in order for TNF-MAb to be dried at a higher product temperature during primary drying. A secondary drying phase at an elevated temperature was necessary in order to achieve optimum moisture content in the final product.     

The freezing step in lyophilization: Physico-chemical fundamentals, freezing methods and consequences on process performance and quality attributes of biopharmaceuticals

Lyophilization is a common, but cost-intensive, drying process to achieve protein formulations with long-term stability. In the past, typical process optimization has focused on the drying steps and the freezing step was rather ignored. However, the freezing step is an equally important step in lyophilization, as it impacts both process performance and product quality.While simple in concept, the freezing step is presumably the most complex step in lyophilization. Therefore, in order to get a more comprehensive understanding of the processes that occur during freezing, the physico-chemical fundamentals of freezing are first summarized. The available techniques that can be used to manipulate or directly control the freezing process in lyophilization are also reviewed. In addition, the consequences of the freezing step on quality attributes, such as sample morphology, physical state of the product, residual moisture content, reconstitution time, and performance of the primary and secondary drying phase, are discussed. A special focus is given to the impact of the freezing process on protein stability.This review aims to provide the reader with an awareness of not only the importance but also the complexity of the freezing step in lyophilization and its impact on quality attributes of biopharmaceuticals and process performance. With a deeper understanding of freezing and the possibility to directly control or at least manipulate the freezing behavior, more efficient lyophilization cycles can be developed, and the quality and stability of lyophilized biopharmaceuticals can be improved.     

Monitoring of the Secondary Drying in Freeze-Drying of Pharmaceuticals

This paper is focused on the in-line monitoring of the secondary drying phase of a lyophilization process. An innovative software sensor is presented to estimate reliably the residual moisture in the product and the time required to complete secondary drying, that is, to reach the target value of the residual moisture or of the desorption rate. Such results are obtained by coupling a mathematical model of the process and the in-line measurement of the solvent desorption rate and by means of the pressure rise test or another sensors (e.g., windmills, laser sensors) that can measure the vapor flux in the drying chamber. The proposed method does not require extracting any vial during the operation or using expensive sensors to measure off-line the residual moisture. Moreover, it does not require any preliminary experiment to determine the relationship between the desorption rate and residual moisture in the product. The effectiveness of the proposed approach is demonstrated by means of experiments carried out in a pilot-scale apparatus: in this case, some vials were extracted from the drying chamber and the moisture content was measured to validate the estimations provided by the soft-sensor.     

Impact of process variables on the micromeritic and physicochemical properties of spray‐dried microparticles – Part II. Physicochemical characterisation of spray‐dried materials

Objectives In this work we investigated the residual organic solvent content and physicochemical properties of spray‐dried chlorothiazide sodium (CTZNa) and potassium (CTZK) salts. Methods The powders were characterised by thermal, X‐ray diffraction, infrared and dynamic vapour sorption (DVS) analyses. Solvent levels were investigated by Karl–Fischer titration and gas chromatography. Key findings Spray‐drying from water, methanol (MeOH) and mixes of MeOH and butyl acetate (BA) resulted in amorphous microparticles. The glass transition temperatures of CTZNa and CTZK were ～192 and ～159°C, respectively. These materials retained their amorphous nature when stored at 25°C in dry conditions for at least 6 months with no chemical decomposition observed. DVS determined the critical relative humidity of recrystallisation of CTZNa and CTZK to be 57% RH and 58% RH, respectively. The inlet temperature dependant oxidation of MeOH to formaldehyde was observed; the formaldehyde was seen to deposit within the amorphous matrix of spray‐dried product. Spray‐drying in the open blowing mode coupled with secondary drying resulted in a three‐fold reduction in residual BA (below pharmacopoeial permitted daily exposure limit) compared to spray‐drying in the closed mode. Conclusions Experiments showed that recirculation of recovered drying gas increases the risk of deposition of residual solvents in the spray‐dried product.     

Practical aspects of lyophilization using non-aqueous co-solvent systems.

Non-aqueous co-solvent systems have been evaluated for their potential use in the freeze-drying of pharmaceutical products. The advantages of using these non-aqueous solvent systems include: increased drug wetting or solubility, increased sublimation rates, increased pre-dried bulk solution or dried product stability, decreased reconstitution time, and enhancement of sterility assurance of the pre-dried bulk solution. Conversely, the potential disadvantages and issues which must be evaluated include: the proper safe handling and storage of flammable and/or explosive solvents, the special facilities or equipment which may be required, the control of residual solvent levels, the toxicity of the remaining solvent, qualification of an appropriate GMP purity, the overall cost benefit to use of the solvent, and the potential increased regulatory scrutiny. The co-solvent system that has been most extensively evaluated was the tert-butanol/water combination. The tert-butanol possesses a high vapor pressure, freezes completely in most commercial freeze-dryers, readily sublimes during primary drying, can increase sublimation rates, and has low toxicity. This co-solvent system has been used in the manufacture of a marketed injectable pharmaceutical product. When using this solvent system, both formulation and process control required optimization to maximize drying rates and to minimize residual solvent levels at the end of drying. Other co-solvent systems which do not freeze completely in commercial freeze-dryers were more difficult to use and often resulted in unacceptable freeze-dried cakes. Their use appears limited to levels of not more than 10%.     

The effect of loading process on product collapse during large-scale lyophilization

Lyophilization is a process commonly used by the pharmaceutical industry in order to enhance product stability by removal of the solvent, typically water. Previous studies have investigated several causes of variability during the lyophilization process, including freezing, vial placement within the lyophilization chamber, primary drying, and secondary drying. These differences can contribute to variability in cake appearance, moisture results, and stability profiles. This study investigates the effect of lyophilization chamber loading on inhomogeneity in final product appearance. For a complex biological product which was initially flash-frozen and subsequently loaded into a large-scale lyophilization chamber, it was found that the method of chamber loading had a significant effect on cake appearance for the first vials loaded into the chamber, which is attributed to inadvertent annealing during the lyophilizer loading step. It is hypothesized that inadvertent annealing led to a decrease in the surface area of the dried cake, which in turn led to product collapse during secondary drying.     

Freeze-Drying Process Design by Manometric Temperature Measurement: Design of a Smart Freeze-Dryer

No HeadingPurpose. To develop a procedure based on manometric temperature measurement (MTM) and an expert system for good practices in freeze drying that will allow development of an optimized freeze-drying process during a single laboratory freeze-drying experiment.Methods. Freeze drying was performed with a FTS Dura-Stop/Dura-Top freeze dryer with the manometric temperature measurement software installed. Five percent solutions of glycine, sucrose, or mannitol with 2 ml to 4 ml fill in 5 ml vials were used, with all vials loaded on one shelf. Details of freezing, optimization of chamber pressure, target product temperature, and some aspects of secondary drying are determined by the expert system algorithms. MTM measurements were used to select the optimum shelf temperature, to determine drying end points, and to evaluate residual moisture content in real-time. MTM measurements were made at 1 hour or half-hour intervals during primary drying and secondary drying, with a data collection frequency of 4 points per second. The improved MTM equations were fit to pressure-time data generated by the MTM procedure using Microcal Origin software to obtain product temperature and dry layer resistance. Using heat and mass transfer theory, the MTM results were used to evaluate mass and heat transfer rates and to estimate the shelf temperature required to maintain the target product temperature.Results. MTM product dry layer resistance is accurate until about two-thirds of total primary drying time is over, and the MTM product temperature is normally accurate almost to the end of primary drying provided that effective thermal shielding is used in the freeze-drying process. The primary drying times can be accurately estimated from mass transfer rates calculated very early in the run, and we find the target product temperature can be achieved and maintained with only a few adjustments of shelf temperature. The freeze-dryer overload conditions can be estimated by calculation of heat/mass flow at the target product temperature. It was found that the MTM results serve as an excellent indicator of the end point of primary drying. Further, we find that the rate of water desorption during secondary drying may be accurately measured by a variation of the basic MTM procedure. Thus, both the end point of secondary drying and real-time residual moisture may be obtained during secondary drying.Conclusions. Manometric temperature measurement and the expert system for good practices in freeze drying does allow development of an optimized freeze-drying process during a single laboratory freeze-drying experiment.     

Spray-drying Nanocapsules in Presence of Colloidal Silica as Drying Auxiliary Agent: Formulation and Process Variables Optimization Using Experimental Designs

Purpose Spray-drying process was used for the development of dried polymeric nanocapsules. The purpose of this research was to investigate the effects of formulation and process variables on the resulting powder characteristics in order to optimize them. Materials and Methods Experimental designs were used in order to estimate the influence of formulation parameters (nanocapsules and silica concentrations) and process variables (inlet temperature, spray-flow air, feed flow rate and drying air flow rate) on spray-dried nanocapsules when using silica as drying auxiliary agent. The interactions among the formulation parameters and process variables were also studied. Responses analyzed for computing these effects and interactions were outlet temperature, moisture content, operation yield, particles size, and particulate density. Additional qualitative responses (particles morphology, powder behavior) were also considered. Results Nanocapsules and silica concentrations were the main factors influencing the yield, particulate density and particle size. In addition, they were concerned for the only significant interactions occurring among two different variables. None of the studied variables had major effect on the moisture content while the interaction between nanocapsules and silica in the feed was of first interest and determinant for both the qualitative and quantitative responses. The particles morphology depended on the feed formulation but was unaffected by the process conditions. Conclusion This study demonstrated that drying nanocapsules using silica as auxiliary agent by spray drying process enables the obtaining of dried micronic particle size. The optimization of the process and the formulation variables resulted in a considerable improvement of product yield while minimizing the moisture content.     

In-line monitoring of granule moisture in fluidized-bed dryers using microwave resonance technology

This is the first report on in-line moisture measurement of pharmaceutical products by microwave resonance technology. In order to meet the FDA’s PAT approach, a microwave resonance sensor appropriate for pharmaceutical use was developed and implemented into two different fluidized-bed dryers. The novel sensor enables a continuous moisture measurement independent from the product density. Hence, for the first time precise real time determination of the moisture in pharmaceutical granules becomes possible. The qualification of the newly developed sensor was performed by drying placebo granules under experimental conditions and the validation using drug loaded granules under real process conditions. The results of the investigations show good correlations between water content of the granules determined by the microwave resonance sensor and both reference methods, loss on drying by infrared light exposure and Karl Fischer titration. Furthermore, a considerable time saving in the drying process was achieved through monitoring the residual water content continuously by microwave resonance technology instead of the formerly used discontinuous methods.     

Moisture and drug solid-state monitoring during a continuous drying process using empirical and mass balance models

Classically, the end point detection during fluid bed drying has been performed using indirect parameters, such as the product temperature or the humidity of the outlet drying air. This paper aims at comparing those classic methods to both in-line moisture and solid-state determination by means of Process Analytical Technology (PAT) tools (Raman and NIR spectroscopy) and a mass balance approach. The six-segmented fluid bed drying system being part of a fully continuous from-powder-to-tablet production line (ConsiGma™-25) was used for this study. A theophylline:lactose:PVP (30:67.5:2.5) blend was chosen as model formulation. For the development of the NIR-based moisture determination model, 15 calibration experiments in the fluid bed dryer were performed. Six test experiments were conducted afterwards, and the product was monitored in-line with NIR and Raman spectroscopy during drying. The results (drying endpoint and residual moisture) obtained via the NIR-based moisture determination model, the classical approach by means of indirect parameters and the mass balance model were then compared. Our conclusion is that the PAT-based method is most suited for use in a production set-up. Secondly, the different size fractions of the dried granules obtained during different experiments (fines, yield and oversized granules) were compared separately, revealing differences in both solid state of theophylline and moisture content between the different granule size fractions.     

注射用还原型谷胱甘肽冻干工艺的优化

为提高注射用还原型谷胱甘肽的稳定性及缩短冻干周期,以冻千时间、产品外观、水分等关键质量属性为指标,对溶剂和干燥温度进行了单因素优化.最终确定采用1％叔丁醇的水溶液作溶剂溶解谷胱甘肽和碳酸氢钠,预冻时隔板温度为-50℃,维持3h至药物全部冻实,再控制一次干燥温度为-36℃,真空度为20 Pa,维持21 h待溶剂完全升华,...     

Impact of Different Elastomer Formulations on Moisture Permeation through Stoppers Used for Lyophilized Products Stored under Humid Conditions

The purpose of this study was to evaluate the effect of moisture permeability of different elastomer formulation stoppers, which had different moisture absorption abilities, on the increase of moisture content inside lyophilized vials during long-term storage under humid conditions. Two different elastomer formulation stoppers (high-moisture and low-moisture uptake stoppers) were compared. The increased amount of moisture content inside lyophilized vials fitted with high-moisture stoppers was higher than those fitted with low-moisture stoppers during the early stage of storage. However, this trend was reversed during the later stage of storage. Our data show that the moisture increase inside the lyophilized vials at the early stage was caused by moisture transfer from the stoppers, whereas the later moisture increase was caused by external moisture permeation through the stoppers. Results indicate that the difference in the moisture uptake profile inside the lyophilized vials at each period of storage was caused by the moisture absorption ability and moisture permeation ability of the two elastomer formulation stoppers. In terms of long-term storage stability under humid conditions, our data indicate that external moisture permeating through the stopper into the lyophilized vial during the late stage was the more important factor. In addition, the increase in moisture content at the early stage was controlled by stopper drying time. Furthermore, stopper drying time did not have an effect on moisture permeation at the late stage. Moisture permeation during the storage period appears to be dependent on the different elastomer formulations of the stoppers. The moisture permeation of different elastomer stoppers was an important factor in terms of the increased moisture content inside the lyophilized vials during the late stage of long-term storage under humid conditions. For lyophilized products stored at room temperature, the moisture permeation ability of the stopper is one of the most important factors for long-term storage stability.     

Feasibility Study on Spray-Drying Protein Pharmaceuticals: Recombinant Human Growth Hormone and Tissue-Type Plasminogen Activator

The feasibility of spray-drying solutions of recombinant methionyl human growth hormone (hGH) and tissue-type plasminogen activator (t-PA) was investigated. hGH was formulated in a mannitol phosphate buffer and t-PA was used in an arginine phosphate formulation containing 0.004% (w/v) polysorbate 80. Using filtered air (90 – 150°C) as the drying medium, hGH could be dried to a residual moisture content of 4%. However, approximately 25% of the protein was degraded during the processing. Results of atomization studies suggest that surface denaturation at the air–liquid interface of the droplets in the spray plays a major role in the degradation of the protein. The addition of 0.1% (w/v) polysorbate 20 into the hGH formulation reduced the formation of soluble and insoluble aggregates by approximately 90% during atomization. During spray-drying the addition of 0.1% (w/v) polysorbate 20 reduced the formation of soluble and insoluble aggregates by approximately 70 and 85%, respectively. In contrast, t-PA remained intact upon atomization. Depending on the spray-drying conditions, product powders with a residual moisture content between 5 and 8% were obtained. No oxidation, aggregation, or denaturation occurred in the protein under several operation conditions. Overall, this study demonstrates that it is feasible to spray-dry t-PA in the current marketed formulation.     

Freeze-drying of tert-butanol/water cosolvent systems: a case report on formation of a friable freeze-dried powder of tobramycin sulfate

A case study is presented in which a tert-butanol (TBA)/water cosolvent system was found to be a useful means of producing freeze-dried tobramycin sulfate that readily forms a loose powder upon agitation in a specialized application in which a critical quality attribute is the ability to pour the sterile powder from the vial. Both formulation and processing variables are important in achieving acceptable physical properties of the cake as well as minimizing residual TBA levels. Liquid/liquid phase separation was observed above critical concentrations of both drug and TBA, resulting in a two-layered lyophilized cake with unacceptable appearance, physical properties, and residual TBA levels. However, the choice of tobramycin sulfate and TBA concentrations in the single-phase region of the phase diagram resulted in a lyophilized solid that can readily be poured from vials. Crystallization of TBA before drying is critical to achieving adequately low residual TBA levels, and this is reflected in the effect of thermal history of freezing on residual TBA levels, where rapid freezing results in incomplete crystallization of TBA and relatively high levels of residual solvent. Annealing at a temperature above T'(g) of the system after an initial freezing step significantly reduces the level of residual TBA. Secondary drying, even at increased temperature and for extended times, is not an effective method of reducing residual TBA levels.     

Reverse Engineering the 1-Month Lupron Depot®

The 1-month Lupron Depot® (LD) encapsulating water-soluble leuprolide in poly(lactic-co-glycolic acid) (PLGA) microspheres is a benchmark product upon which modern long-acting release products are often compared. Despite expiration of patent coverage, no generic product for the LD has been approved in the USA, likely due to the complexity of components and manufacturing processes involved in the product. Here, we describe the reverse engineering of the LD composition and important product attributes. Specific attributes analyzed for microspheres were as follows: leuprolide content by three methods; gelatin content, type, and molecular weight distribution; PLGA content, lactic acid/glycolic acid ratio, and molecular weight distribution; mannitol content; in vitro drug release; residual solvent and moisture content; particle size distribution and morphology; and glass transition temperature. For the diluent, composition, viscosity, and specific gravity were analyzed. Analyzed contents of the formulation and the determined PLGA characteristics matched well with the official numbers stated in the package insert and those found in literature, respectively. The gelatin was identified as type B consistent with ~?300 bloom. The 11-μm volume-median microspheres in the LD slowly released the drug in vitro in a zero-order manner after ~?23% initial burst release. Very low content of residual moisture (<?0.5%) and methylene chloride (<?1 ppm) in the product indicates in-water drying is capable of removing solvents to extremely low levels during manufacturing. The rigorous approach of reverse engineering described here may be useful for development of generic leuprolide-PLGA microspheres as well as other new and generic PLGA microsphere formulations.     

Cryoprotectants for freeze drying of drug nano-suspensions: Effect of freezing rate

Drug nanoparticles are often prepared in a liquid medium, and a drying method such as freeze drying is used to convert them to an oral solid dosage form. When the dried form is reconstituted in an aqueous system, it may be redispersed to achieve its original particle size. The redispersibility of dried nanoparticles depends on the parameters of the freeze drying process. In this study, an apparatus with a freezing rate gradient was used to systematically investigate the effect of cryoprotectants on the redispersibility of nanoparticles as a function of freezing rate. Sucrose, lactose, mannitol, and polyethylene glycol were used as cryoprotectants for a naproxen nano-suspension. A fast freezing rate and a high cryoprotectant concentration were generally favored. However, under certain conditions, a slower freezing rate resulted in better redispersibility. This is probably because slow freezing can produce a more cryo-concentrated liquid phase, and the concentrated cryoprotectant in the liquid phase can more effectively protect the nanoparticles. An irreversible aggregation map was constructed as a function of the freezing rate and the cryoprotectant concentration, and shows both the favorable and unfavorable effects of cryoprotectants. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4808–4817, 2009