Wouter L. J. Hinrichs

Development of stable influenza vaccine powder formulations: challenges and possibilities.

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine.

A comparison between spray drying and spray freeze drying to produce an influenza subunit vaccine powder for inhalation

The aim of this study was to investigate two different processes to produce a stable influenza subunit vaccine powder for pulmonary immunization i.e. spray drying (SD) and spray freeze drying (SFD). The formulations were analyzed by proteolytic assay, single radial immunodiffusion assay (SRID), cascade impactor analysis, and immunization studies in Balb/c mice. Proteolytic assay and SRID analysis showed that antigen integrity after SFD was best conserved when the formulation was buffered by Hepes buffer saline (HBS). Surprisingly, antigen integrity after SD was better conserved when the formulation was buffered by phosphate buffer saline (PBS) rather than by HBS. The dispersion from the dry powder inhaler, the Twincer, resulted in a fine particle fraction (aerodynamic particle size <5microm) of 37% and 23% for spray dried and spray freeze dried powders, respectively. Immunogenicity of both vaccine formulations (SFD/HBS and SD/PBS) was similar to conventional liquid formulation after i.m. immunization. In addition, compared to i.m. immunizations, the pulmonary immunization with the dry powders resulted in significantly higher IgG titers. Furthermore, both the formulations remained biochemically and physically stable for at least 3years of storage at 20 degrees C. Our results demonstrate that both optimized formulations are stable and have good inhalation characteristics.

Needle-free influenza vaccination

Vaccination is the cornerstone of influenza control in epidemic and pandemic situations. Influenza vaccines are typically given by intramuscular injection. However, needle-free vaccinations could offer several distinct advantages over intramuscular injections: they are pain-free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs. Moreover, vaccine delivery via the respiratory tract, alimentary tract, or skin might elicit mucosal immune responses at the site of virus entry and better cellular immunity, thus improving effectiveness. Although various needle-free vaccination methods for influenza have shown preclinical promise, few have progressed to clinical trials-only live attenuated intranasal vaccines have received approval, and only in some countries. Further clinical investigation is needed to help realise the potential of needle-free vaccination for influenza.

Inulin, a flexible oligosaccharide I: Review of its physicochemical characteristics

Inulin, a fructan-type polysaccharide, consists of (2→1) linked β-d-fructosyl residues (n=2-60), usually with an (1↔2) α-d-glucose end group. The applications of inulin and its hydrolyzed form oligofructose (n=2-10) are diverse. It is widely used in food industry to modify texture, replace fat or as low-calorie sweetener. Additionally, it has several applications in other fields like the pharmaceutical arena. Most notably it is used as a diagnostic agent for kidney function and as a protein stabilizer. This work reviews the physicochemical characteristics of inulin that make it such a versatile substance. Topics that are addressed include morphology (crystal morphology, crystal structure, structure in solution); solubility; rheology (viscosity, hydrodynamic shape, gelling); thermal characteristics and physical stability (glass transition temperature, vapor sorption, melting temperature) and chemical stability. When using inulin, the degree of polymerization and processing history should be taken into account, as they have a large impact on physicochemical behavior of inulin.

Towards tailored vaccine delivery: Needs, challenges and perspectives

The ideal vaccine is a simple and stable formulation which can be conveniently administered and provides life-long immunity against a given pathogen. The development of such a vaccine, which should trigger broad and strong B-cell and T-cell responses against antigens of the pathogen in question, is highly dependent on tailored vaccine delivery approaches. This review addresses vaccine delivery in its broadest scope. We discuss the needs and challenges in the area of vaccine delivery, including restrictions posed by specific target populations, potentials of dedicated stable formulations and devices, and the use of adjuvants. Moreover, we address the current status and perspectives of vaccine delivery via several routes of administration, including non- or minimally invasive routes. Finally we suggest possible directions for future vaccine delivery research and development.

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.

Strongly enhanced dissolution rate of fenofibrate solid dispersion tablets by incorporation of superdisintegrants

In this study, it was shown that the incorporation of superdisintegrants in solid dispersion tablets containing a high drug load can strongly enhance the dissolution rate of the highly lipophilic drug fenofibrate. In addition, the dissolution rate was more increased when the superdisintegrant was incorporated in the drug containing solid dispersions than when it was physically mixed with the solid dispersions. The dissolution rate enhancement strongly depended on the type of superdisintegrants and increased in the order Polyplasdone XL-10<Polyplasdone XL<<Ac-Di-Sol approximately Primojel. The dissolution behavior also depended on the type of hydrophilic carriers. Solid dispersion tablets based on inulin 4 kDa, polyethylene glycol 20K and polyvinylpyrrolidone K30 showed a much faster dissolution than those based on mannitol and hydroxypropyl-beta-cyclodextrin. Finally, inulin 4 kDa-based solid dispersion tablets showed excellent storage stability, while polyethylene glycol 20K-and polyvinylpyrrolidone K30-based solid dispersion tablets did not.

Development of a dried influenza whole inactivated virus vaccine for pulmonary immunization.

Stabilization and ease of administration are two ways to substantially improve the use of current vaccines. In the present study an influenza whole inactivated virus (WIV) vaccine was freeze-dried or spray-freeze dried in the presence of inulin as a cryoprotectant. Only spray-freeze drying rendered powders compatible with administration to the lungs by insufflation. Pulmonary administration of the powder vaccine obtained by this method to BALB/c mice led to a transient influx of neutrophils and a concomitant decrease in the number of macrophages as did administration of liquid vaccine. Inflammatory reactions to both vaccines were mild and short-lived. Immunization studies showed that the immunogenic properties of WIV vaccine were not affected by drying. Pulmonary administration of the powder WIV vaccine induced a systemic immune response of the same magnitude as liquid vaccine while mucosal IgA responses were higher for powder WIV. In a challenge study where immunized mice were exposed to a lethal dose of live virus, two pulmonary doses of either liquid or powder WIV vaccine were equally effective as a single intramuscular injection of subunit vaccine in terms of reduction of the viral load in the lungs. To conclude, in the models employed for these studies the use of a dry powder WIV vaccine for pulmonary immunization was shown to be safe and efficient.

Unraveling protein stabilization mechanisms: Vitrification and water replacement in a glass transition temperature controlled system

The aim of this study was to elucidate the role of the two main mechanisms used to explain the stabilization of proteins by sugar glasses during drying and subsequent storage: the vitrification and the water replacement theory. Although in literature protein stability is often attributed to either vitrification or water replacement, both mechanisms could play a role and they should be considered simultaneously. A model protein, alkaline phosphatase, was incorporated in either inulin or trehalose by spray drying. To study the storage stability at different glass transition temperatures, a buffer which acts as a plasticizer, ammediol, was incorporated in the sugar glasses. At low glass transition temperatures (<50°C), the enzymatic activity of the protein strongly decreased during storage at 60°C. Protein stability increased when the glass transition temperature was raised considerably above the storage temperature. This increased stability could be attributed to vitrification. A further increase of the glass transition temperature did not further improve stability. In conclusion, vitrification plays a dominant role in stabilization at glass transition temperatures up to 10 to 20°C above storage temperature, depending on whether trehalose or inulin is used. On the other hand, the water replacement mechanism predominantly determines stability at higher glass transition temperatures.

Characterization of a cyclosporine solid dispersion for inhalation

For lung transplant patients, a respirable, inulin-based solid dispersion containing cyclosporine A (CsA) has been developed. The solid dispersions were prepared by spray freezedrying. The solid dispersion was characterized by water vapor uptake, specific surface area analysis, and particle size analysis. Furthermore, the mode of inclusion of CsA in the dispersion was investigated with Fourier transform infrared spectroscopy. Finally, the dissolution behavior was determined and the aerosol that was formed by the powder was characterized. The powder had large specific surface areas (∼160 m2). The water vapor uptake was dependent linearly on the drug load. The type of solid dispersion was a combination of a solid solution and solid suspension. At a 10% drug load, 55% of the CsA in the powder was in the form of a solid solution and 45% as solid suspension. At 50% drug load, the powder contained 90% of CsA as solid suspension. The powder showed excellent dispersion characteristics as shown by the high emitted fraction (95%), respirable fraction (75%), and fine-particle fraction (50%). The solid dispersions consisted of relatively large (x50≈7 μm), but low-density particles (ρ≈0.2 g/cm3). The solid dispersions dissolved faster than the physical mixture, and inulin dissolved faster than CsA. The spray freeze-drying with inulin increased the specific surface area and wettability of CsA. In conclusion, the developed powder seems suitable for inhalation in the local treatment of lung transplant patients.