The tangential flow absorption model (TFAM) - A novel dissolution method for evaluating the performance of amorphous solid dispersions of poorly water-soluble actives.

There is a substantial demand for absorptive dissolution tests, as single vessel dissolution experiments were originally not designed for testing supersaturating systems. Current approaches suffer from inadequate mass transfer of the dissolved active from the dissolution site, discrepancies in the fluid volume compared to in vivo intestinal fluid volumes or the dilution of functional excipients. In this work a novel dissolution apparatus was developed that enables adjustable mass transfer of the active through a membrane, while retaining the functional polymeric excipients at the dissolution site. Using this setup the dissolution behavior of various spray dried amorphous solid dispersions containing carbamazepine, hydrochlorothiazide and ketoconazole as model actives at intermediate and high supersaturation levels was evaluated. Compared to non-absorptive dissolution experiments, differences in the concentration-time profiles were noted. The experiments with a high supersaturation of ketoconazole revealed a concentration decrease over time under absorptive conditions. Additionally, it was observed that the difference between "spring" as well as "spring and parachute" formulations was less pronounced with increasing drug efflux. Further, the apparatus was also tested with Fasted State Simulated Intestinal Fluid as dissolution medium and results were compared to phosphate buffer pH6.8. As major benefits of the new TFAM apparatus the easy experimental procedure and sample preparation for drug concentration measurements using spectroscopy in the permeate, without the necessity for additional filtration and/or centrifugation to remove precipitated drug molecules, could be highlighted. This TFAM approach seems to be a promising tool for identifying formulations for amorphous solid dispersions with optimal in vitro performance.

The influence of polymer excipients on the dissolution and recrystallization behavior of ketoconazole: Application, variation and practical aspects of a pH shift method.

The formulation of amorphous solid dispersions (ASDs) is an effective way to improve the bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs). The combination of an amorphous state of the drug and the presence of crystallization-inhibiting polymers retains a high amount of dissolved API over time. ASDs with ketoconazole and different polymers were manufactured by spray drying and their characteristics as well as performance were analyzed. Dissolution tests with a change of the dissolution medium from 0.1 M HCl to phosphate buffer at pH 6.8 to simulate pH conditions for instant release formulations, and a direct dissolution of the ASDs in phosphate buffer pH 6.8 to simulate conditions for an enteric formulation, were performed. All ASDs with API contents between 25 and 50% by weight were completely X-ray amorphous. Varying dissolution behaviors between medium change and direct dissolution occurred. It was possible to identify the superior ASD-compositions for both types of tests. The acidic polymers methacrylic acid-ethyl acrylate copolymer, hypromellose acetate succinate and the solubilizer macrogolglycerol hydroxystearate showed the best performances. The combination of the acidic polymers with macrogolglycerol hydroxystearate showed an improved dissolution behavior at higher API contents. The optimization of such formulations with different release-patterns plays an important role for the enhancement of the oral bioavailability of poorly water-soluble drugs.

Alternative vaccine administration by powder injection: Needle-free dermal delivery of the glycoconjugate meningococcal group Y vaccine.

Powder-injectors use gas propulsion to deposit lyophilised drug or vaccine particles in the epidermal and sub epidermal layers of the skin. We prepared dry-powder (Tg = 45.2 ± 0.5°C) microparticles (58.1 µm) of a MenY-CRM197 glyconjugate vaccine (0.5% wt.) for intradermal needle-free powder injection (NFPI). SFD used ultrasound atomisation of the liquid vaccine-containing excipient feed, followed by lyophilisation above the glass transition temperature (Tg' = - 29.9 ± 0.3°C). This resulted in robust particles (density~ 0.53 ±0.09 g/cm3) with a narrow volume size distribution (mean diameter 58.1 µm, and span = 1.2), and an impact parameter (ρvr ~ 11.5 kg/m·s) sufficient to breach the Stratum corneum (sc). The trehalose, manitol, dextran (10 kDa), dextran (150 kDa) formulation, or TMDD (3:3:3:1), protected the MenY-CRM197 glyconjugate during SFD with minimal loss, no detectable chemical degradation or physical aggregation. In a capsular group Y Neisseria meningitidis serum bactericidal assay (SBA) with human serum complement, the needle free vaccine, which contained no alum adjuvant, induced functional protective antibody responses in vivo of similar magnitude to the conventional vaccine injected by hypodermic needle and syringe and containing alum adjuvant. These results demonstrate that needle-free vaccination is both technically and immunologically valid, and could be considered for vaccines in development.

Needle-Free Dermal Delivery of a Diphtheria Toxin CRM197 Mutant on Potassium-Doped Hydroxyapatite Microparticles.

Injections with a hypodermic needle and syringe (HNS) are the current standard of care globally, but the use of needles is not without limitation. While a plethora of needle-free injection devices exist, vaccine reformulation is costly and presents a barrier to their widespread clinical application. To provide a simple, needle-free, and broad-spectrum protein antigen delivery platform, we developed novel potassium-doped hydroxyapatite (K-Hap) microparticles with improved protein loading capabilities that can provide sustained local antigen presentation and release. K-Hap showed increased protein adsorption over regular hydroxyapatite (P < 0.001), good structural retention of the model antigen (CRM197) with 1% decrease in α-helix content and no change in ß-sheet content upon adsorption, and sustained release in vitro. Needle-free intradermal powder inoculation with K-Hap-CRM197 induced significantly higher IgG1 geometric mean titers (GMTs) than IgG2a GMTs in a BALB/c mouse model (P < 0.001) and induced IgG titer levels that were not different from the current clinical standard (P > 0.05), namely, alum-adsorbed CRM197 by intramuscular (i.m.) delivery. The presented results suggest that K-Hap microparticles may be used as a novel needle-free delivery vehicle for some protein antigens.

Intradermal powder immunization with protein-containing vaccines.

The central importance for global public health policy of delivering life-saving vaccines for all children makes the development of efficacious and safe needle-free alternatives to hypodermic needles, preferably in a thermostable form, a matter of pressing urgency. This paper comprehensively reviews past in vivo studies on intradermal powder immunization with vaccine formulations that do not require refrigeration. Particular emphasis is given to the immune response in relation to antigen adjuvantation. While needle-free intradermal delivery of vaccines induces a predominantly Th2-type immune response, adjuvants powerfully enhance and modulate the magnitude and nature of the elicited immune response at various effector sites.

Real-time optical measurement of biologically relevant thermal damage in tissue-mimicking hydrogels containing bovine serum albumin.

PURPOSE: In controlled laboratory studies of hyperthermia and thermal ablation, translucent hydrogels containing bovine serum albumin (BSA) are often employed as tissue-mimicking materials due to the change in their opacity that takes place as they accumulate heat damage. In this work we demonstrate the biological relevance of this optical metric of thermal damage, as well as establish the physical mechanisms that link it with quantifiable damage to the proteins embedded in the gel. MATERIALS AND METHODS: We applied Fourier transform infrared (FTIR) spectroscopy, turbidity analysis using ultraviolet-visible (UV/VIS) spectroscopy, and size exclusion chromatography (SEC) to samples of heat-treated, aqueous bovine serum albumin (BSA). We also measured the rates of survival in heated suspensions of breast cancer cells using a colorimetric assay. RESULTS: Using FTIR spectroscopy and SEC, we show that the intermolecular beta-sheet content of the protein ensemble rises in heat treatments above 60 degrees C, which causes aggregate formation. Furthermore, by applying UV/VIS spectroscopy we demonstrate that the opacity of the hydrogel increases past 60 degrees C due to the formation of insoluble protein aggregates that scatter incident light. Finally, we illustrate that the viability of human breast cancer cells follows a similar trend to measurements of BSA polyacrylamide hydrogel opacity at various temperatures from 37 degrees C to 90 degrees C. CONCLUSIONS: Our work establishes a causal link between the degree of BSA denaturation in hydrogel and the opacity of the medium. Furthermore, our results demonstrate that BSA hydrogels provide a simple physical model for quantifying biologically relevant heat damage in real time during controlled laboratory studies of hyperthermia and thermal ablation.

An acoustic microscopy technique to assess particle size and distribution following needle-free injection.

Needle-free injection is a novel technique for transdermal drug and vaccine delivery, the efficacy of which depends on the number density and mean penetration depth of particles beneath the skin. To date, these parameters have been assessed optically, which is time-consuming and unsuitable for use in vivo. The present work describes the development of a scanning acoustic microscopy technique to map and size particle distributions following injection. Drug particles were modeled using a polydisperse distribution of polystyrene spheres, mean diameter 30.0 mum, and standard deviation 16.7 mum, injected into agar-based tissue-mimicking material, and later, as polydisperse stainless steel spheres, mean diameter 46.0 mum, and standard deviation 13.0 mum, injected both into agar and into porcine skin. A focused broadband immersion transducer (10-75 MHz), driven in pulse-echo mode, was scanned over the surface of the injected samples. Recorded echo signals were post-processed to deduce particle penetration depth (30-300 mum). Furthermore, post-injection size distribution of the spheres was calculated using a novel, automated spectral analysis technique. Experimental results were validated optically and found to predict penetration depth and particle size accurately. The availability of simultaneous particle penetration depth and particle size information makes it possible for the first time to optimize particle design for specific drug delivery applications.