Drug delivery strategies for poorly water-soluble drugs: the industrial perspective

INTRODUCTION: For poorly soluble compounds, a good bioavailability is typically needed to assess the therapeutic index and the suitability of the compound for technical development. In industry, the selection of the delivery technology is not only driven by technical targets, but also by constraints, such as production costs, time required for development and the intellectual property situation. AREAS COVERED: This review covers current developments in parenteral and oral delivery technologies and products for poorly water-soluble compounds, such as nano-suspensions, solid dispersions and liposomes. In addition, the use of biorelevant dissolution media to assess dissolution and solubility properties is described. Suggestions are also included to systematically address development hurdles typical of poorly water-soluble compounds intended for parenteral or oral administration. EXPERT OPINION: A holistic assessment is recommended to select the appropriate delivery technology by taking into account technical as well as intellectual property considerations. Therefore, first and foremost, a comprehensive physico-chemical characterization of poorly water-soluble compounds can provide the key for a successful selection and development outcome. In this context, the identified physical form of the compound in the formulation is used as a guide for a risk-benefit assessment of the selected oral delivery technology. The potential of nano-suspensions for intravenous administration is unclear. In the case of oral administration, nano-suspensions are mainly used to improve the oral absorption characteristics of micronized formulations. The development of an in situ instantaneous solubilization method, based on stable, standardized liposomes with low toxicity, opens new avenues to solubilize poorly water-soluble compounds.     

Oral formulation strategies to improve solubility of poorly water-soluble drugs

Introduction: In the past two decades, there has been a spiraling increase in the complexity and specificity of drug–receptor targets. It is possible to design drugs for these diverse targets with advances in combinatorial chemistry and high throughput screening. Unfortunately, but not entirely unexpectedly, these advances have been accompanied by an increase in the structural complexity and a decrease in the solubility of the active pharmaceutical ingredient. Therefore, the importance of formulation strategies to improve the solubility of poorly water-soluble drugs is inevitable, thus making it crucial to understand and explore the recent trends.

Areas covered: Drug delivery systems (DDS), such as solid dispersions, soluble complexes, self-emulsifying drug delivery systems (SEDDS), nanocrystals and mesoporous inorganic carriers, are discussed briefly in this review, along with examples of marketed products. This article provides the reader with a concise overview of currently relevant formulation strategies and proposes anticipated future trends.

Expert opinion: Today, the pharmaceutical industry has at its disposal a series of reliable and scalable formulation strategies for poorly soluble drugs. However, due to a lack of understanding of the basic physical chemistry behind these strategies, formulation development is still driven by trial and error.     

改善难溶性药物功效的一种新型给药系统——干酏剂的研究进展

干酏剂是一种将乙醇和药物同时包裹入水溶性聚合物壳内的固态微囊.乙醇的潜溶剂作用及喷雾干燥工艺可能产生的无定形药物,有利于包裹于干酏剂中的水难溶性药物快速分散并溶解于水性介质中,从而提高其溶出速率和生物利用度.本文综合近年来干酏剂研究的主要文献,从干酏剂的制剂成型工艺及机制、对难溶性药物体外溶出、体内吸收及生物利用度的影响,以及基于干酏剂的剂型设计及应用做一综述.     

Drug delivery strategies for poorly water-soluble drugs

The drug candidates coming from combinatorial chemistry research and/or the drugs selected from biologically based high-throughput screening are quite often very lipophilic, as these drug candidates exert their pharmacological action at or in biological membranes or membrane-associated proteins. This challenges drug delivery institutions in industry or academia to develop carrier systems for the optimal oral and parenteral administration of these drugs. To mention only a few of the challenges for this class of drugs: their oral bioavailability is poor and highly variable, and carrier development for parenteral administration is faced with problems, including the massive use of surface-active excipients for solubilisation. Formulation specialists are confronted with an even higher level of difficulties when these drugs have to be delivered site specifically. This article addresses the emerging formulation designs for delivering of poorly water-soluble drugs.     

纳米给药系统在难溶性药物制剂研究中的应用

近年来,难溶性药物给药系统一直是制剂学研究的重点和难点之一。纳米载体由于其良好的生物相容性及可装载大量难溶性药物等特点而被广泛应用于难溶性药物给药系统的研究,该类载体主要包括纳米粒、脂质体、纳米乳、聚合物胶束、纳米混悬剂等。本文结合近几年国内外文献报道,对纳米给药系统在难溶性药物制剂研究中的最新进展进行概述。     

应用纳米技术增加难溶性药物吸收的研究进展

随着高通量筛选等新技术的出现,涌现出许多难溶性的候选药物。利用纳米技术能减小难溶性药物的粒径,增加其溶解度、溶出度和口服生物利用度,减少食物效应的影响。本文介绍了纳米粒的制备方法,商用的专利纳米技术以及应用纳米技术成功上市的药品。纳米技术对改善生物药剂学分类体系（BCS）Ⅱ类药物的吸收具有广阔的前景。     

纳米晶体技术在水难溶性药物口服制剂中应用的研究进展

目的综述水难溶性药物纳米晶体的制备方法,稳定剂在纳米晶体形成过程中的主要应用原理及产品物理性质的表征,为改善水难溶性药物溶解度或口服生物利用度提供理论依据。方法查阅国内外相关文献27篇,回顾纳米晶体技术的发展历程,提供药物纳米晶体技术的最新研究进展。结果药物纳米晶体不仅制备工艺简单,性质考察方便;还能够提高难溶性药物在胃肠道中的溶解度,改善难溶性药物的口服生物利用度。结论药物纳米晶体技术具有实际生产意义和广阔的应用前景。     

Amphiphilic polymeric micelles as the nanocarrier for peroral delivery of poorly soluble anticancer drugs

Introduction: Many amphiphilic copolymers have recently been synthesized as novel promising micellar carriers for the delivery of poorly water-soluble anticancer drugs. Studies on the formulation and oral delivery of such micelles have demonstrated their efficacy in enhancing drug uptake and absorption, and exhibit prolonged circulation time in vitro and in vivo.

Areas covered: In this review, literature on hydrophobic modifications of several hydrophilic polymers, including polyethylene glycol, chitosan, hyaluronic acid, pluronic and tocopheryl polyethylene glycol succinate, is summarized. Parameters influencing the properties of polymeric micelles for oral chemotherapy are discussed and strategies to overcome main barriers for polymeric micelles peroral absorption are proposed.

Expert opinion: During the design of polymeric micelles for peroral chemotherapy, selecting or synthesizing copolymers with good compatibility with the drug is an effective strategy to increase drug loading and encapsulation efficiency. Stability of the micelles can be improved in different ways. It is recommended to take permeability, mucoadhesion, sustained release, and P-glycoprotein inhibition into consideration during copolymer preparation or to consider adding some excipients in the formulation. Furthermore, both the copolymer structure and drug loading methods should be controlled in order to get micelles with appropriate particle size for better absorption.     

Lipid-based formulations for oral administration of poorly water-soluble drugs

Lipid-based drug delivery systems have shown great potentials in oral delivery of poorly water-soluble drugs, primarily for lipophilic drugs, with several successfully marketed products. Pre-dissolving drugs in lipids, surfactants, or mixtures of lipids and surfactants omits the dissolving/dissolution step, which is a potential rate limiting factor for oral absorption of poorly water-soluble drugs. Lipids not only vary in structures and physiochemical properties, but also in their digestibility and absorption pathway; therefore selection of lipid excipients and dosage form has a pronounced effect on the biopharmaceutical aspects of drug absorption and distribution both in vitro and in vivo. The aim of this review is to provide an overview of the different lipid-based dosage forms from a biopharmaceutical point of view and to describe effects of lipid dosage forms and lipid excipients on drug solubility, absorption and distribution.     

A comparative study on the effects of amphiphilic and hydrophilic polymers on the release profiles of a poorly water-soluble drug

This paper reports the use of two crystalline polymers, an amphiphilic Pluronic® F-127 (PF-127) and a hydrophilic poly(ethylene glycol) (PEG6000) as drug delivery carriers for improving the drug release of a poorly water-soluble drug, fenofibrate (FEN), via micelle formation and formation of a solid dispersion (SD). In 10% PF-127 (aq.), FEN showed an equilibrium solubility of ca. 0.6?mg/mL, due to micelle formation. In contrast, in 10% PEG6000 (aq.), FEN only exhibited an equilibrium solubility of 0.0037?mg/mL. FEN-loaded micelles in PF-127 were prepared by direct dissolution and membrane dialysis. Both methods only yielded a highest drug loading (DL) of 0.5%. SDs of FEN in PF-127 and PEG6000, at DLs of 5–80%, were prepared by solvent evaporation. In-vitro dissolution testing showed that both micelles and SDs significantly improved FEN’s release rate. The SDs of FEN in PF-127 showed significantly faster release than crystalline FEN, when the DL was as high as 50%, whereas SDs of PEG6000 showed similar enhancement in the release rate when the DL was not more than 20%. The DSC thermograms of SDs of PF-127 exhibited a single phase transition peak at ca. 55–57?°C when the DL was not more than 50%, whereas those in PEG6000 exhibited a similar peak at ca. 61–63?°C when the DL was not more than 35%. When the DL exceeded 50% for SDs of PF-127 and 35% for SDs of PEG6000, DSC thermograms showed two melting peaks for the carrier polymer and FEN, respectively. FT-IR studies revealed that PF-127 has a stronger hydrophobic–hydrophobic interaction with FEN than PEG6000. It is likely that both dispersion and micelle formation contributed to the stronger effect of PF-127 on enhancing the release rate of FEN in its SDs.     

Preparation of starch macrocellular foam for increasing the dissolution rate of poorly water-soluble drugs

Starch macrocellular foam (SMF), a novel natural bio-matrix material, was prepared by the hard template method in order to improve the dissolution rate and oral bioavailability of poorly water-soluble drugs. Nitrendipine (NDP) was chosen as a model drug and was loaded into SMF by the solvent evaporation method. SMF and the loaded SMF samples (NDP-SMF) were characterized by scanning electron microscopy, differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy. In vitro drug release studies showed that SMF significantly increased the dissolution rate of NDP. In vivo studies showed that the NDP-SMF tablets clearly increased the oral bioavailability of NDP in comparison with the reference commercial tablets. All the results obtained demonstrated that SMF was a promising carrier for the oral delivery of poor water-soluble drugs.     

Solid dispersions,Part II: new strategies in manufacturing methods for dissolution rate enhancement of poorly water-soluble drugs

Introduction: The absorption of poorly water-soluble drugs, when presented in the crystalline state to the gastrointestinal tract, is typically dissolution rate-limited, and according to BCS these drugs belong mainly to class II. Both dissolution kinetics and solubility are particle size dependent. Nowadays, various techniques are available to the pharmaceutical industry for dissolution rate enhancement of such drugs. Among such techniques, nanosuspensions and drug formulation in solid dispersions are those with the highest interest.

Areas covered: This review discusses strategies undertaken over the last 10 years, which have been applied for the dissolution enhancement of poorly water-soluble drugs; such processes include melt mixing, electrospinning, microwave irradiation and the use of inorganic nanoparticles.

Expert opinion: Many problems in this field still need to be solved, mainly the use of toxic solvents, and for this reason the use of innovative new procedures and materials will increase over the coming years. Melt mixing remains extremely promising for the preparation of SDs and will probably become the most used method in the future for the preparation of solid drug dispersions.     

Microemulsions as drug delivery systems to improve the solubility and the bioavailability of poorly water-soluble drugs

Importance of the field: Microemulsions have been studied extensively as potential drug delivery vehicles for poorly water-soluble drugs. An understanding of the physicochemical and biopharmaceutical characteristics of the microemulsions according to administration routes will provide guidance for designing the formulations of microemulsions.

Areas covered in this review: In this paper, the use and the characteristics of microemulsions as drug delivery vehicles are reviewed. As the formulations of the microemulsion always include a great amount of surfactant and co-surfactant, which may cause hemolysis or histopathological alterations of the tissue, the potential toxicity or the irritancy of microemulsions is also discussed in this paper.

What the reader will gain: Developments of microemulsions for poorly water-soluble drugs in recent years are included in this review. Several factors limiting the commercial or clinical use of microemulsions are also discussed.

Take home message: Considering the potential in enhanced drug uptake/permeation and facing the limitations, their unique properties make microemulsions a promising vehicle for poorly water-soluble drugs.     

Drug delivery strategies for Alzheimer's disease treatment

Introduction: Current Alzheimer's disease (AD) therapy is based on the administration of the drugs donepezil, galantamine, rivastigmine and memantine. Until disease-modifying therapies become available, further research is needed to develop new drug delivery strategies to ensure ease of administration and treatment persistence.

Areas covered: In addition to the conventional oral formulations, a variety of drug delivery strategies applied to the treatment of AD are reviewed in this paper, with a focus on strategies leading to simplified dosage regimens and to providing new pharmacological tools. Alternatives include extended release, orally disintegrating or sublingual formulations, intranasal or short- and long-acting intramuscular or transdermal forms, and nanotechnology-based delivery systems.

Expert opinion: The advent of new research on molecular mechanisms of AD pathogenesis has outlined new strategies for therapeutic intervention; these include the stimulation of α-secretase cleavage, the inhibition of γ-secretase activity, the use of non-steroidal anti-inflammatory drugs, neuroprotection based on antioxidant therapy, the use of estrogens, NO synthetase inhibitors, and natural agents such as polyphenols. Unfortunately, these compounds might not help patients with end stage AD, but might hopefully slow or stop the disease process in its early stage. Nanotechnologies may prove to be a promising contribution in future AD drug delivery strategies, in particular drug carrier nano- or microsystems, which can limit the side effects of anti-Alzheimer drugs.     

Drug delivery systems for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a severe immune-mediated disease characterized by chronically progressive inflammation and destruction of joints and associated structures. Significant advances in our understanding of its pathophysiology and early diagnosis have led to improved therapy and better outcome. Nevertheless, a number of details in the pathogenesis of RA are still unknown and thus the disease cannot be cured at present. Therefore, current therapy aims at accomplishing complete and long-lasting remission. However, this goal is only achieved in a small proportion of patients, and partial remission and frequent relapses are a common problem. A significant number of patients still do not respond at all to available treatments. In addition, all antirheumatic and immune-modulating drugs developed so far carry a considerable risk of adverse effects, some of which can be severe or even life threatening. This is due, at least in part, to a lack of specificity of most drugs for the target tissue, and to a high volume of distribution for systemic application, which, together with rapid clearance of most drugs, requires frequent application of high dosages. Targeted drug delivery and prolongation of bioavailability would alleviate this issue significantly. This article, therefore, reviews a selection of studies that report promising strategies for joint specific delivery of antiarthritic drugs.     

Nanocrystals for enhancement of oral bioavailability of poorly water-soluble drugs

Nanocrystals, a carrier-free colloidal delivery system in nano-sized range, is an interesting approach for poorly soluble drugs. Nanocrystals provide special features including enhancement of saturation solubility, dissolution velocity and adhesiveness to surface/cell membranes. Several strategies are applied for nanocrystals production including precipitation, milling, high pressure homogenization and combination methods such as NanoEdge™, SmartCrystal and Precipitation-lyophilization-homogenization (PLH) technology. For oral administration, many publications reported useful advantages of nanocrystals to improve in vivo performances i.e. pharmacokinetics, pharmacodynamics, safety and targeted delivery which were discussed in this review. Additionally, transformation of nanocrystals to final formulations and future trends of nanocrystals were also described.