The role of the carrier in the formulation of pharmaceutical solid dispersions. Part I: crystalline and semi-crystalline carriers

ABSTRACT

Introduction: As a consequence of the target and drug candidate identification process, drugs with higher hydrophobicity and/or lipophilicity are being selected for further development, leading to solubility and dissolution rate limited oral bioavailability, and hence potential failure of the intended therapeutic goal. Solid dispersions were introduced as a formulation strategy in the early 1960s to tackle this issue and are still an area of intensive research activity.

Areas covered: There has been a shift in the type of carriers that were used in the formulation of solid dispersions as nowadays, amorphous carriers are most often used, whereas in early stages of solid dispersions development, crystalline and semi-crystalline carriers were most commonly applied. In this review, we will discuss several aspects related to the use of crystalline and semi-crystalline carriers such as their molecular and related physical structure, and their physical chemical properties related to formulation of poorly soluble drugs.

Expert opinion: The inherent crystallinity of this type of carrier hinders the formation of high-load solid solutions as mainly the amorphous domains of a carrier are able to accommodate drug molecules. Hence these carriers are not currently first choice excipients to formulate solid dispersions.     

Exploring the feasibility of the use of biopolymers as a carrier in the formulation of amorphous solid dispersions – Part I: Gelatin

Biopolymers have rarely been used so far as carriers in the formulation of amorphous solid dispersions (ASD) to overcome poor solubility of active pharmaceutical ingredients (APIs). In an attempt to enlarge our knowledge on this topic, gelatin, type 50PS was selected. A screening study was initiated in which twelve structurally different poorly soluble biopharmaceutical classification system (BCS) Class II drugs (carbamazepine, cinnarizine, diazepam, itraconazole, nifedipine, indomethacin, darunavir (ethanolate), ritonavir, fenofibrate, griseofulvin, ketoconazole and naproxen) were selected for evaluation. Solid dispersions of five different drug loadings of these twelve compounds were prepared by lyophilization and evaluated for their solid state properties by mDSC and XR(P)D, and in vitro dissolution performance. Even without any process optimization it was possible to form either fully amorphous or partially amorphous systems, depending on the API and API to carrier ratio. Hence in this respect, gelatin 50PS behaves as any other carrier. Dissolution of the API from the solid dispersions significantly exceeded that of their crystalline counterparts. This study shows the potential of gelatin as a carrier to formulate amorphous solid dispersions.     

Overcoming formulation challenges for the next generation of vaccines

Introduction: In recent years, the number of active pharmaceutical ingredients with high therapeutic impact, but very low water solubility, has increased significantly. Thus, a great challenge for pharmaceutical technology is to create new formulations and efficient drug-delivery systems to overcome these dissolution problems.

Areas covered: Drug formulation in solid dispersions (SDs) is one of the most commonly used techniques for the dissolution rate enhancement of poorly water-soluble drugs. Generally, SDs can be defined as a dispersion of active ingredients in molecular, amorphous and/or microcrystalline forms into an inert carrier. This review covers literature which states that the dissolution enhancement of SDs is based on the fact that drugs in the nanoscale range, or in amorphous phase, dissolve faster and to a greater extent than micronized drug particles. This is in accordance to the Noyes–Whitney equation, while the wetting properties of the used polymer may also play an important role.

Expert opinion: The main factors why SD-based pharmaceutical products on the market are steadily increasing over the last few years are: the recent progress in various methods used for the preparation of SDs, the effect of evolved interactions in physical state of the drug and formulation stability during storage, the characterization of the physical state of the drug and the mechanism of dissolution rate enhancement.     

Manufacturing of solid dispersions of poorly water soluble drugs by spray drying: Formulation and process considerations

Spray drying is an efficient technology for solid dispersion manufacturing since it allows extreme rapid solvent evaporation leading to fast transformation of an API-carrier solution to solid API-carrier particles. Solvent evaporation kinetics certainly contribute to formation of amorphous solid dispersions, but also other factors like the interplay between the API, carrier and solvent, the solution state of the API, formulation parameters (e.g. feed concentration or solvent type) and process parameters (e.g. drying gas flow rate or solution spray rate) will influence the final physical structure of the obtained solid dispersion particles. This review presents an overview of the interplay between manufacturing process, formulation parameters, physical structure, and performance of the solid dispersions with respect to stability and drug release characteristics.     

基于HPMCAS载体的依非韦伦固体分散体溶出模式研究

目的 以依非韦伦为原料药、不同规格（L、M、H）HPMCAS为载体，采用喷雾干燥法制备固体分散体并对其溶出模式进行初步探究。方法 通过X射线粉末衍射（XRPD）、扫描电子显微镜（SEM）对固体分散体理化性质进行制剂学表征；以动力溶解度为指标考察不同药载比、不同规格HPMCAS固体分散体的溶出情况；通过粒度分析仪和透射电子显微镜（TEM）、SEM探讨固体分散体溶出时的不同模式。结果 XRPD分析显示，固体分散体中药物以无定形的形态分散在HPMCAS中；SEM分析显示，L、M、H规格HPMCAS与依非韦伦形成的固体分散体均具有"萎缩葡萄干"形态；在pH 6.8磷酸缓冲盐溶液中溶出时，药载比1：6的固体分散体溶出好，药载比1：1.5的固体分散体溶出差且相同药载比时L规格HPMCAS的固体分散体溶出更快。结论 以不同规格HPMCAS为载体制备的依非韦伦固体分散体在pH 6.8磷酸缓冲盐溶液中溶出时，存在多种溶出模式。药载比1：6时，L、M规格HPMCAS的固体分散体以药物纳米颗粒的形式溶出；药载比1：1.5时，L、M规格HPMCAS的固体分散体存在类似溶蚀的溶出模式，药物从载体骨架中释放。     

Improved dissolution behavior of lipophilic drugs by solid dispersions: the production process as starting point for formulation considerations

Introduction: Many new drug substances have low aqueous solubility which can cause poor bioavailability after oral administration. The application of solid dispersions is a useful method to increase the dissolution rate of these drugs and thereby improve their bioavailability. So far, several methods have been developed to prepare solid dispersions. To obtain a product with the desired attributes, both the formulation and production processes should be considered.

Areas covered: The most currently used methods to produce solid dispersions, such as the fusion method, hot melt extrusion, spray drying, freeze drying and supercritical fluid precipitation, are reviewed in this paper. In addition, the physicochemical characteristics of the obtained solid dispersions are discussed.

Expert opinion: Solid dispersions can be successfully prepared by simple fusion, hot melt extrusion, spray drying, freeze drying and supercritical fluid precipitation. Hot melt extrusion, spray drying and freeze drying are processes that can be applied for large scale production. The simple fusion method is not very suitable for large scale production, but is particularly suitable for screening formulations. The most recent method to produce sold dispersions is supercritical fluid precipitation. The process conditions of this method need extensive investigation, in particular in relationship with the selection of the type of carrier and/or solvent. Both processes and formulation aspects strongly affect the characteristics of solid dispersion products. Furthermore, application of crystalline solid dispersions is gaining increasing interest because they are thermodynamically more stable than amorphous solid dispersions.     

On the inherent properties of Soluplus and its application in ibuprofen solid dispersions generated by microwave-quench cooling technology

Abstract

Polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer, or Soluplus^®, is a relatively new copolymer and a promising carrier of amorphous solid dispersions. Knowledge on the inherent properties of Soluplus^® (e.g. cloud points, critical micelle concentrations, and viscosity) in different conditions is relatively inadequate, and the application characteristics of Soluplus^®-based solid dispersions made by microwave methods still need to be clarified. In the present investigation, the inherent properties of a Soluplus^® carrier, including cloud points, critical micelle concentrations, and viscosity, were explored in different media and in altered conditions. Ibuprofen, a BCS class II non-steroidal anti-inflammatory drug, was selected to develop Soluplus^®-based amorphous solid dispersions using the microwave-quench cooling (MQC) method. Scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Raman spectroscopy (RS), and Fourier transform infrared spectroscopy (FT-IR) were adopted to analyze amorphous properties and molecular interactions in ibuprofen/Soluplus^® amorphous solid dispersions generated by MQC. Dissolution, dissolution extension, phase solubility, equilibrium solubility, and supersaturated crystallization inhibiting experiments were performed to elucidate the effects of Soluplus^® on ibuprofen in solid dispersions. This research provides valuable information on the inherent properties of Soluplus^® and presents a basic understanding of Soluplus^® as a carrier of amorphous solid dispersions.     

Dissolution enhancement of felodipine by amorphous nanodispersions using an amphiphilic polymer: insight into the role of drug–polymer interactions on drug dissolution

Context: Felodipine, a poorly soluble drug, is widely used in the treatment of angina pectoris and hypertension.

Objective: This study aimed at the preparation of amorphous solid dispersion (SD) of felodipine using an amphiphilic polymer, soluplus, for the potential enhancement in solubility of the drug.

Materials and methods: Solid dispersions with varying proportions of drug and soluplus were prepared and the rate and extent of dissolution from SDs was compared with that of the pure drug. FT-IR and ¹H NMR spectroscopic analysis were carried out to examine the formation mechanism of SDs. Various techniques were used for solid state characterization of designed SDs.

Results: Formation of amorphous solid dispersions with particle size in nanometer range indicated suitability of polymer and method used in the preparation. FT-IR and ¹H NMR spectroscopy revealed that soluplus was involved in strong hydrogen bonding with felodipine molecules which resulted in the conversion of crystalline felodipine into amorphous form. Solid dispersion with 1:10 drug/polymer ratio showed more than 90% drug dissolution in 30?min whereas pure felodipine showed less than 19% drug dissolution in 1?h.

Discussion and conclusion: Amorphous SDs of felodipine were prepared using soluplus resulting in substantial enhancement in the rate and extent of dissolution of felodipine.     

Coamorphous Active Pharmaceutical Ingredient–Small Molecule Mixtures: Considerations in the Choice of Coformers for Enhancing Dissolution and Oral Bioavailability

In the recent years, coamorphous systems, containing an active pharmaceutical ingredient (API) and a small molecule coformer have appeared as alternatives to the use of either amorphous solid dispersions containing polymer or cocrystals of API and small molecule coformers, to improve the dissolution and oral bioavailability of poorly soluble crystalline API. This Commentary article considers the relative properties of amorphous solid dispersions and coamorphous systems in terms of methods of preparation; miscibility; glass transition temperature; physical stability; hygroscopicity; and aqueous dissolution. It also considers important questions concerning the fundamental criteria to be used for the proper selection of a small molecule coformer regarding its ability to form either coamorphous or cocrystal systems. Finally, we consider various aspects of product development that are specifically associated with the formulation of commercial coamorphous systems as solid oral dosage forms. These include coformer selection; screening; methods of preparation; preformulation; physical stability; bioavailability; and final formulation. Through such an analysis of coamorphous API-small molecule coformer systems, against the more widely studied API-polymer dispersions and cocrystals, it is believed that the strengths and weaknesses of coamorphous systems can be better understood, leading to more efficient formulation and manufacture of such systems for enhancing oral bioavailability.     

The effect of physico-chemical properties of the drug on the pharmaceutical availability of piroxicam from pellets

The aim of this study was to develop the formulation of pellets with solid dispersions of piroxicam, and determine the effect of physico-chemical properties of the drug on pharmaceutical availability from solid dispersions and pellets. Two types of piroxicam, varying in crystal size, were used in this study. Presence of the amorphous form in solid dispersions depended on the method of their formulation, and type of piroxicam used. Based on the results of piroxicam release rate from pellets, it was established that the extrusion and spheronization process caused change in the drug release profile in comparison to powder systems, because during the pelletization process, the amorphous form of the piroxicam present in the solid dispersion recrystallizes, and a low-solubility type forms. Better results were obtained using the method, where microcrystalline cellulose cores were coated with solid dispersion.     

The effect of physico-chemical properties of the drug on the pharmaceutical availability of piroxicam from pellets

The aim of this study was to develop the formulation of pellets with solid dispersions of piroxicam, and determine the effect of physico-chemical properties of the drug on pharmaceutical availability from solid dispersions and pellets. Two types of piroxicam, varying in crystal size, were used in this study. Presence of the amorphous form in solid dispersions depended on the method of their formulation, and type of piroxicam used. Based on the results of piroxicam release rate from pellets, it was established that the extrusion and spheronization process caused change in the drug release profile in comparison to powder systems, because during the pelletization process, the amorphous form of the piroxicam present in the solid dispersion recrystallizes, and a low-solubility type forms. Better results were obtained using the method, where microcrystalline cellulose cores were coated with solid dispersion.     

大黄素固体分散体制备、表征与释药机制研究

摘要：目的 制备大黄素固体分散体，提高其体外溶出度并探究其释药机制。方法 采用分子对接技术，辅助筛选聚合物载体。以大黄素为原料药，Kollidon VA64为聚合物载体，采用热熔挤出工艺制备大黄素固体分散体。通过溶出仪测定其体外溶出，利用SEM，DCS和PXRD对原料药和固体分散体的表面形态和晶型进行表征，最后采用FTIR，NMR和分子动力学模拟对固体分散体的释药机制进行探究。结果 相较于大黄素原料药，大黄素固体分散体在4种介质中的溶出被明显改善，大黄素由结晶态转化为无定形态，药物与聚合物载体间形成了氢键。结论 固体分散体中药物晶型的转变和氢键的产生是改善药物体外溶出的主要因素。     

The dissolution enhancement of piroxicam in its physical mixtures and solid dispersion formulations using gluconolactone and glucosamine hydrochloride as potential carriers

Abstract

The solid dispersion technique is one of the most effective methods for improving the dissolution rate of poorly water-soluble drugs; however this is reliant on a suitable carrier and solvent being selected. The work presented explores amino sugars (d-glucosamine HCl and d-gluconolactone) as potential hydrophilic carriers to improve dissolution rate of a poorly water-soluble drug, piroxicam, from physical mixtures and solid dispersion formulations. Solid dispersions of the drug and carrier were prepared using different ratios by the conventional solvent evaporation method. Acetone was used as solvent in the preparation of solid dispersions. Physical mixtures of piroxicam and carrier were also prepared for comparison. The properties of all solid dispersions and physical mixtures were studied using a dissolution tester, Fourier transform infrared, XRD, SEM and differential scanning calorimetry. These results showed that the presence of glucosamine or gluconolactone can increase dissolution rate of piroxicam compared to pure piroxicam. Glucosamine or Gluconolactone could be used as carrier in solid dispersion formulations and physical mixtures to enhance the dissolution rate. Solid state studies showed that no significant changes occurred for piroxicam in physical mixtures and solid dispersion.     

Refining stability and dissolution rate of amorphous drug formulations

Introduction: Poor aqueous solubility of active pharmaceutical ingredients (APIs) is one of the main challenges in the development of new small molecular drugs. Additionally, the proportion of poorly soluble drugs among new chemical entities is increasing. The transfer of a crystalline drug to its amorphous counterpart is often seen as a potential solution to increase the solubility. However, amorphous systems are physically unstable. Therefore, pharmaceutical formulations scientists need to find ways to stabilise amorphous forms.

Areas covered: The use of polymer-based solid dispersions is the most established technique for the stabilisation of amorphous forms, and this review will initially focus on new developments in this field. Additionally, newly discovered formulation approaches will be investigated, including approaches based on the physical restriction of crystallisation and crystal growth and on the interaction of APIs with small molecular compounds rather than polymers. Finally, in situ formation of an amorphous form might be an option to avoid storage problems altogether.

Expert opinion: The diversity of poorly soluble APIs formulated in an amorphous drug delivery system will require different approaches for their stabilisation. Thus, increased focus on emerging techniques can be expected and a rational approach to decide the correct formulation is needed.     

Producing Amorphous Solid Dispersions via Co-Precipitation and Spray Drying: Impact to Physicochemical and Biopharmaceutical Properties

Many small-molecule active pharmaceutical ingredients (APIs) exhibit low aqueous solubility and benefit from generation of amorphous dispersions of the API and polymer to improve their dissolution properties. Spray drying and hot-melt extrusion are 2 common methods to produce these dispersions; however, for some systems, these approaches may not be optimal, and it would be beneficial to have an alternative route. Herein, amorphous solid dispersions of compound A, a low-solubility weak acid, and copovidone were made by conventional spray drying and co-precipitation. The physicochemical properties of the 2 materials were assessed via X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, and scanning electron microscopy. The amorphous dispersions were then formulated and tableted, and the performance was assessed in vivo and in vitro. In human dissolution studies, the co-precipitation tablets had slightly slower dissolution than the spray-dried dispersion, but both reached full release of compound A. In canine in vitro dissolution studies, the tablets showed comparable dissolution profiles. Finally, canine pharmacokinetic studies showed that the materials had comparable values for the area under the curve, bioavailability, and C_max. Based on the summarized data, we conclude that for some APIs, co-precipitation is a viable alternative to spray drying to make solid amorphous dispersions while maintaining desirable physicochemical and biopharmaceutical characteristics.     

穿心莲内酯聚丙烯酸树脂Ⅱ固体分散体的制备及表征

目的：研究无定形聚合物聚丙烯酸树脂Ⅱ（Eudragit Ⅱ）制备的穿心莲内酯固体分散体的优良性质,为固体分散体的载体选择提供参考依据。方法：以无定形聚合物Eudragit Ⅱ为载体材料,按穿心莲内酯-载体质量比为1：3,采用喷雾干燥法制备穿心莲内酯固体分散体,并用傅里叶变换红外光谱（FTIR）、热重分析（TG）、X-射线衍射（XRD）、差示扫描量热（DSC）、扫描电镜（SEM）、比表面积、粒径和溶出度测定穿心莲内酯固体分散体的理化性质及溶出行为。结果：FTIR光谱和TG分析说明在穿心莲内酯固体分散体和物理混合物中穿心莲内酯与Eudragit Ⅱ之间都存在分子间相互作用,其中穿心莲固体分散体具有更好的热稳定性;DSC和XRD分析说明无定形载体Eudragit Ⅱ制备的固体分散体中穿心莲内酯主要以无定形形式存在;SEM显示,固体分散体中穿心莲内酯由块状晶体形态变为了不规则的圆形形态;同时与物理混合物相比,穿心莲内酯固体分散体具有更大的比表面积、更大的孔体积和更小的粒径等粉体学性质;溶出实验表明穿心莲内酯固体分散体具有增大溶出的优势,效果明显。结论：以无定形载体Eudragit Ⅱ制备的穿心莲内酯固体分散体具有优良的理化性质,同时比表面积大,孔体积大的特征更有利于水分子的进入,从而有效地增大穿心莲内酯的溶出速率。     

A proposal for a drug product Manufacturing Classification System (MCS) for oral solid dosage forms

Abstract

This paper proposes the development of a drug product Manufacturing Classification System (MCS) based on processing route. It summarizes conclusions from a dedicated APS conference and subsequent discussion within APS focus groups and the MCS working party. The MCS is intended as a tool for pharmaceutical scientists to rank the feasibility of different processing routes for the manufacture of oral solid dosage forms, based on selected properties of the API and the needs of the formulation. It has many applications in pharmaceutical development, in particular, it will provide a common understanding of risk by defining what the “right particles” are, enable the selection of the best process, and aid subsequent transfer to manufacturing. The ultimate aim is one of prediction of product developability and processability based upon previous experience.

This paper is intended to stimulate contribution from a broad range of stakeholders to develop the MCS concept further and apply it to practice. In particular, opinions are sought on what API properties are important when selecting or modifying materials to enable an efficient and robust pharmaceutical manufacturing process. Feedback can be given by replying to our dedicated e-mail address (mcs@apsgb.org); completing the survey on our LinkedIn site; or by attending one of our planned conference roundtable sessions.     

Investigation of Ethylene Oxide-co-propylene Oxide for Dissolution Enhancement of Hot-Melt Extruded Solid Dispersions

The optimal design of amorphous solid dispersion formulations requires the use of excipients to maintain supersaturation and improve physical stability to ensure shelf-life stability and better absorption during intestinal transit, respectively. Blends of excipients (surfactants and polymers) are often used within pharmaceutical products to improve the oral delivery of Biopharmaceutical Classification System class II drugs. Therefore, in this study, a dissolution enhancer, poloxamer 407 (P407), was investigated to determine its effect on the dissolution properties and on the amorphous nature of the active pharmaceutical ingredient contained in the formulation. Phase solubility studies of indomethacin (INM) in aqueous solutions of P407 and poly(vinylpyrrolidone-vinyl acetate copolymer) showed an increase in the kinetic solubility of INM compared with the pure drug at 37°C with a K_a value of 0.041 μg/mL. The solid dispersions showed a higher dissolution rate when compared to pure and amorphous drugs when performed in pH buffer 1.2 with a kinetic solubility of 21 μg/mL. The stability data showed that the amorphous drug in solid solutions with poly(vinylpyrrolidone-vinyl acetate copolymer) and P407 remained amorphous, and the %P407 loading had no effect on the amorphous stability of INM. This study concluded that the amorphous solid dispersion contributed to the increased solubility of INM.     

Evaluating Spray Drying and Co-Precipitation as Manufacturing Processes for Amorphous Solid Dispersions of a Low Tg API

Amorphous solid dispersions feature prominently in the approach to mitigate low bioavailability of poorly water-soluble small molecules, particularly in the early development space focusing on toxicity evaluations and clinical studies in normal healthy volunteers, where high exposures are needed to establish safety margins. Spray drying has been the go-to processing route for a number of reasons, including ubiquitous availability of equipment, the ability to accommodate small scale deliveries, and established processes for delivering single phase amorphous material. Active pharmaceutical ingredients (APIs) with low glass transition temperatures (T_g) can pose challenges to this approach. This study addresses multiple routes towards overcoming issues encountered with a low T_g (∼ 12 °C) API during manufacture of a spray dry intermediate (SDI). Even once formulated as an amorphous solid dispersion (ASD) with HPMCAS-LG, the T_g of the ASD was sufficiently low to require the use of non-ideal solvents, posing safety concerns and ultimately resulting in low yields with frequent process interruptions to resolve product build-up. To resolve challenges with spray drying the HPMCAS-L SDI, higher T_g polymers were assessed during spray drying, and an alternative antisolvent precipitation-based process was evaluated to generate co-precipitated amorphous dispersions (cPAD) with either HPMCAS-L or the additional higher T_g polymers. Both approaches were found to be viable alternatives to achieve single phase ASDs while demonstrating comparable in vitro and in vivo bioperformance compared to the SDI. The results of this effort offer valuable considerations for future early-stage activities for ASDs with low T_g APIs.