Effect of Excipients on Salt Disproportionation during Dissolution: A Novel Application of In Situ Raman Imaging.

We have employed a bespoke setup combining confocal Raman microscopy and an ultraviolet-visible (UV-Vis) spectroscopy flow cell to investigate the effect of excipients on the disproportionation kinetics of Pioglitazone HCl (PioHCl) in tablets during dissolution. Three binary formulations of PioHCl, containing citric acid monohydrate (CA), lactose monohydrate (LM), or magnesium stearate (MgSt), respectively, were used as models to study the influence of excipients' physicochemical properties on the rate of salt disproportionation kinetics and dissolution performance in different aqueous pH environments. It was found that formulation excipients can induce or prevent salt disproportionation by modulating the microenvironmental pH regardless of the pH of the dissolution media. Incorporating CA in PioHCl tablets preserves the salt form and enhances the dissolution performance of the salt in the acidic medium (pH = 1.2). In contrast, LM and MgSt had a detrimental effect on in vitro drug performance by inducing salt disproportionation in the tablet during dissolution in the same acidic medium. Dissolution in the neutral medium (pH = 6.8) showed rapid formation of the free base upon contact with the dissolution medium. The Raman maps of the cross-sectioned tablets revealed the formation of a shell consisting of the free base around the edge of the tablet. This shell decreased the rate of penetration of the dissolution medium into the tablet, which had significant implications on the release of the API into the surrounding solution, as shown by the UV-vis absorption spectroscopy drug release data. Our findings highlight the utility of the Raman/UV-vis flow cell analytical platform as an advanced analytical technique to investigate the effect of excipients and dissolution media on salt disproportionation in real time. This methodology will be used to enhance our understanding of salt stability studies that may pave the way for more stable multicomponent formulations.

Poly (Glycerol Adipate): From a Functionalized Nanocarrier to a Polymeric-Prodrug Matrix to Create Amorphous Solid Dispersions.

Amorphous solid dispersions are a promising strategy to overcome poor solubility and stability limitations, reducing the crystallinity of the drug through incorporation within a polymer matrix. However, to achieve an effective amorphous solid dispersion, the polymer and drug must be compatible, otherwise the drug can undergo recrystallization. In this work, we investigated the potential of the enzymatically synthesized poly(glycerol-adipate), as a pharmaceutical tool for producing a nanoamorphous formulation. A polymeric prodrug of poly(glycerol-adipate) was synthesized by coupling mefenamic acid as drug. The amorphicity of the polymeric prodrug was assessed combining differential scanning calorimetry and polarized optical microscopy. The prodrug was then formulated into nanoparticles and studied for stability and drug release in the presence of lipase. To realize the goal of combination drug therapies for overcoming drug resistance and improving treatment outcomes, the prodrug was screened as a solubility enhancer for a series of fenamic drugs and compared with commercially available polymers commonly used in solid dispersions. Screening was carried out by developing a high-throughput miniaturized screening assay using a 2D printer to dispense the polymer and drug combinations. Finally, the collected data showed that drug conjugation could improve drug-polymer compatibility, in addition to facilitating the release of drugs by 2 different mechanisms.

Investigation of Potential Amorphisation and Co-Amorphisation Behaviour of the Benzene Di-Carboxylic Acids upon Cryo-Milling.

Multi-component formulations offer a way to modulate the physico-chemical properties of drug molecules and thereby enhance their efficacy as medicines compared to using only the raw drug, with mechano-chemical synthesis being an increasingly popular way to create these novel materials in a research setting. However, to date studies have focussed on employing pharmaceutically acceptable components, which has led to the literature featuring chemically diverse pairings of drug and excipient. Here we investigate the outcome of cryo-milling and co-cryo-milling of a series of three simple geometrical isomers of benzene di-carboxylic acid with a view to developing a chemically simple model system to investigate areas including cryo-milling, co-cryo-milling, co-amorphous formulation, etc. All three single-component materials exhibit differing behaviour upon cryo-milling and subsequent storage, as do the two-component mixtures. The surprisingly differing behaviours of these chemically similar species upon cryo-milling and co-cryo-milling suggest that molecular chemistry may not be the dominant influence on the outcome of mechano-chemical syntheses, and that other properties should be explored to develop a predictive model for the outcomes of these types of reactions.

Application of biorelevant saliva-based dissolution for optimisation of orally disintegrating formulations of felodipine.

The oral cavity is of great importance to the performance of orally retained formulations, including: orally disintegrating tablets, taste-masked formulations, and buccal/sublingual delivery systems. With regards to in vitro dissolution assessment of these dosage forms, human saliva should be represented by the dissolution media. Currently there is no general consensus regarding oral cavity dissolution. In this study pooled human saliva was characterised and utilised as dissolution media for biorelevant oral cavity dissolution studies and to assess drug release. Lipophilic drug felodipine with challenging biopharmaceutical properties was selected for assessment in oral cavity dissolution studies. These saliva dissolution studies investigated for the first time how biorelevant dissolution can be implemented as a screening tool to guide the formulation development process and to predict dosage form performance within the mouth. In this study a combination of three dissolution enhancement strategies (cryomilling, solid dispersion, and inclusion complexation) were employed to eventually increase the concentration of felodipine in saliva 150-fold. Using this successful formulation strategy orally disintegrating tablets of felodipine were produced. Interestingly, the percentage release of felodipine in compendial dissolution apparatus was shown to be over 80% after 10 min. On the other hand, saliva-based dissolution showed that percentage release of felodipine was only 0.2% after 10 min using the same formulation. This discrepancy in drug release between dissolution media highlights the need for biorelevant dissolution apparatus for the oral cavity to reliably assess performance of relevant dosage forms in vitro.

Water Solubility Enhancement of Pyrazolo[3,4-d]pyrimidine Derivatives via Miniaturized Polymer-Drug Microarrays.

A miniaturized assay was optimized to evaluate the enhanced apparent water solubility of pyrazolo[3,4-d]pyrimidine derivatives used extensively as anticancer drug scaffolds. The applied amount of drugs used in the reported strategy ranged from 5 to 10 µg per formulation which were dispensed by an inkjet 2D printer directly into a 96-well plate. The selected polymer/drug formulations with high water solubility demonstrated improved cytotoxicity against a human lung adenocarcinoma cancer cell line (A549) compared to the free drugs. We attribute the enhanced efficacy to the improved apparent-solubility of the drug molecules achieved via this methodology. This novel miniaturized method showed promising results in terms of water solubility improvement of the highly hydrophobic pyrazolo[3,4-d]pyrimidine derivatives, requiring only a few micrograms of each drug per tested polymeric formulation. In addition, the reported experimental evidence may facilitate identification of suitable polymers for combination with drug, leading to investigations on biological properties or mechanisms of action in a single formulation.

Rapid Nanogram Scale Screening Method of Microarrays to Evaluate Drug-Polymer Blends Using High-Throughput Printing Technology.

A miniaturized, high-throughput assay was optimized to screen polymer-drug solid dispersions using a 2-D Inkjet printer. By simply printing nanoliter amounts of polymer and drug solutions onto an inert surface, drug/polymer microdots of tunable composition were produced in an easily addressable microarray format. The amount of material printed for each dried spot ranged from 25 ng to 650 ng. These arrays were used to assess the stability of drug/polymer dispersions with respect to recrystallization, using polarized light microscopy. One array with a panel of 6 drugs formulated at different ratios with a poly(vinylpyrrolidone-vinyl acetate) (PVPVA) copolymer was developed to estimate a possible bulk (gram-scale) approximation threshold from the final printed nanoamount of formulation. Another array was printed at a fixed final amount of material to establish a literature comparison of one drug formulated with different commercial polymers for validation. This new approach may offer significant efficiency in pharmaceutical formulation screening, with each experiment in the nanomicro-array format requiring from 3 up to 6 orders of magnitude lower amounts of sample than conventional screening methods.

Indomethacin-Kollidon VA64 Extrudates: A Mechanistic Study of pH-Dependent Controlled Release.

Because of its weakly acidic nature (pKa of 4.5), indomethacin presents an aqueous solubility that significantly increases when changing from acidic to neutral/alkaline pH (1.5 µg/mL at pH 1.2 and 105.2 µg/mL at pH 7.4). We have therefore investigated the impact of the dissolution medium pH on the dissolution performance of indomethacin:Kollidon VA64 extrudates. The impact of the drug loading on the dissolution properties of these systems was also examined (5%, 15%, 30%, 50%, 70%, and 90% drug loading). Time-resolved Raman spectroscopy along with in-line UV-vis spectrophotometry was employed to directly relate changes in dissolution behavior to physicochemical changes that occur to the extrudate during the test. The dissolution tests were performed in pH 2 HCl (to mimic the stomach conditions), and this was then switched during the experiment to pH 6.8 phosphate buffer (to simulate the poststomach conditions). The rotating disc dissolution rate test was also used to simultaneously measure the dissolution rate of both the drug and the polymer. We found that in pH 2 HCl buffer, for the 15% or higher drug-loaded extrudates, Kollidon VA64 preferentially dissolves from the exterior of the compact leaving an amorphous drug-rich hydrophobic shell, which, similarly to an enteric coating, inhibits the drug release. The in situ formation of an enteric coating has been previously hypothesized, and this has been the first time that is directly observed in a pH-variable dissolution test. The dissolution medium switch to pH 6.8 phosphate buffer, due to the large increase of the aqueous solubility of indomethacin at this pH, leads to rapid dissolution of the material forming the coating and therefore total drug release. In contrast, the 5% extrudate is fully hydrated and quickly dissolves at low pH pointing to a dissolution performance dependent on highly water-soluble Kollidon VA64.

Properties of acyl modified poly(glycerol-adipate) comb-like polymers and their self-assembly into nanoparticles.

There is an increasing need to develop bio-compatible polymers with an increased range of different physicochemical properties. Poly(glycerol-adipate) (PGA) is a biocompatible, biodegradable amphiphilic polyester routinely produced from divinyl adipate and unprotected glycerol by an enzymatic route, bearing a hydroxyl group that can be further functionalized. Polymers with an average Mn of ∼13 kDa can be synthesized without any post-polymerization deprotection reactions. Acylated polymers with fatty acid chain length of C4, C8, and C18 (PGAB, PGAO, and PGAS, respectively) at different degrees of substitution were prepared. These modifications yield comb-like polymers that modulate the amphiphilic characteristics of PGA. This novel class of biocompatible polymers has been characterized through various techniques such as FT-IR, 1H NMR, surface, thermal analysis, and their ability to self-assemble into colloidal structures was evaluated by using DLS. The highly tunable properties of PGA reported herein demonstrate a biodegradable polymer platform, ideal for engineering solid dispersions, nanoemulsions, or nanoparticles for healthcare applications. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3267-3278.

Investigating the Dissolution Performance of Amorphous Solid Dispersions Using Magnetic Resonance Imaging and Proton NMR.

We have investigated the dissolution performance of amorphous solid dispersions of poorly water-soluble bicalutamide in a Kollidon VA64 polymeric matrix as a function of the drug loading (5% vs. 30% bicalutamide). A combined suite of state-of-the-art analytical techniques were employed to obtain a clear picture of the drug release, including an integrated magnetic resonance imaging UV-Vis flow cell system and 1H-NMR. Off-line 1H-NMR was used for the first time to simultaneously measure the dissolution profiles and rates of both the drug and the polymer from a solid dispersion. MRI and 1H-NMR data showed that the 5% drug loading compact erodes linearly, and that bicalutamide and Kollidon VA64 are released at approximately the same rate from the molecular dispersion. For the 30% extrudate, data indicated a slower water ingress into the compact which corresponds to a slower dissolution rate of both bicalutamide and Kollidon VA64.

3D printing of five-in-one dose combination polypill with defined immediate and sustained release profiles.

We have used three dimensional (3D) extrusion printing to manufacture a multi-active solid dosage form or so called polypill. This contains five compartmentalised drugs with two independently controlled and well-defined release profiles. This polypill demonstrates that complex medication regimes can be combined in a single personalised tablet. This could potentially improve adherence for those patients currently taking many separate tablets and also allow ready tailoring of a particular drug combination/drug release for the needs of an individual. The polypill here represents a cardiovascular treatment regime with the incorporation of an immediate release compartment with aspirin and hydrochlorothiazide and three sustained release compartments containing pravastatin, atenolol, and ramipril. X-ray powder diffraction (XRPD) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) were used to assess drug-excipient interaction. The printed polypills were evaluated for drug release using USP dissolution testing. We found that the polypill showed the intended immediate and sustained release profiles based upon the active/excipient ratio used.

3D printing of tablets containing multiple drugs with defined release profiles.

We have employed three-dimensional (3D) extrusion-based printing as a medicine manufacturing technique for the production of multi-active tablets with well-defined and separate controlled release profiles for three different drugs. This 'polypill' made by a 3D additive manufacture technique demonstrates that complex medication regimes can be combined in a single tablet and that it is viable to formulate and 'dial up' this single tablet for the particular needs of an individual. The tablets used to illustrate this concept incorporate an osmotic pump with the drug captopril and sustained release compartments with the drugs nifedipine and glipizide. This combination of medicines could potentially be used to treat diabetics suffering from hypertension. The room temperature extrusion process used to print the formulations used excipients commonly employed in the pharmaceutical industry. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray powder diffraction (XRPD) were used to assess drug-excipient interaction. The printed formulations were evaluated for drug release using USP dissolution testing. We found that the captopril portion showed the intended zero order drug release of an osmotic pump and noted that the nifedipine and glipizide portions showed either first order release or Korsmeyer-Peppas release kinetics dependent upon the active/excipient ratio used.

Insights into the influence of the cooling profile on the reconstitution times of amorphous lyophilized protein formulations.

Lyophilized protein formulations must be reconstituted back into solution prior to patient administration and in this regard long reconstitution times are not ideal. The factors that govern reconstitution time remain poorly understood. The aim of this research was to understand the influence of the lyophilization cooling profile (including annealing) on the resulting cake structure and reconstitution time. Three protein formulations (BSA 50mg/ml, BSA 200mg/ml and IgG1 40mg/ml, all in 7% w/v sucrose) were investigated after cooling at either 0.5°C/min, or quench cooling with liquid nitrogen with/without annealing. Significantly longer reconstitution times were observed for the lower protein concentration formulations following quench cool. Porosity measurements found concomitant increases in the surface area of the porous cake structure but a reduction in total pore volume. We propose that slow reconstitution results from either closed pores or small pores impeding the penetration of water into the lyophilized cake.

The influence of polymer content on early gel-layer formation in HPMC matrices: The use of CLSM visualisation to identify the percolation threshold.

Percolation theory has been used for several years in the design of HPMC hydrophilic matrices. This theory predicts that a minimum threshold content of polymer is required to provide extended release of drug, and that matrices with a lower polymer content will exhibit more rapid drug release as a result of percolation pathways facilitating the faster penetration of the aqueous medium. At present, percolation thresholds in HPMC matrices have been estimated solely through the mathematical modelling of dissolution data. This paper examines whether they can be also identified in a novel way: through the use of confocal laser scanning fluorescence microscopy (CLSM) to observe the morphology of the emerging gel layer during the initial period of polymer hydration and early gel formation at the matrix surface. In this study, matrices have been prepared with a polymer content of 5-30% w/w HPMC 2208 (Methocel K4M), with a mix of other excipients (a soluble drug (caffeine), lactose, microcrystalline cellulose and magnesium stearate) to provide a typical industrially realistic formulation. Dissolution studies, undertaken in water using USP apparatus 2 (paddle) at 50rpm, provided data for the calculation of the percolation threshold through relating dissolution kinetic parameters to the excipient volumetric fraction of the dry matrix. The HPMC percolation threshold estimated this way was found to be 12.8% v/v, which was equivalent to a matrix polymer content of 11.5% w/w. The pattern of polymer hydration and gel layer growth during early gel layer formation was examined by confocal laser scanning fluorescence microscopy (CLSM). Clear differences in gel layer formation were observed. At polymer contents above the estimated threshold a continuous gel layer was formed within 15min, whereas matrices with polymer contents below the threshold were characterised by irregular gel layer formation with little evidence of HPMC particle coalescence. According to percolation theory, this implies that a continuous cluster of HPMC particles was not formed. The images provide the first direct evidence of how the percolation threshold may be related to the success or failure of early gel layer development in HPMC matrices. It also shows how extended release characteristics are founded on the successful coalescence of hydrated polymer particles to form a continuous coherent diffusion barrier, which can then inhibit further percolation of the hydration medium. The correlation between percolation thresholds estimated from dissolution and imaging techniques suggests that confocal imaging may provide a more rapid method for estimating the percolation thresholds, facilitating the rational design of HPMC extended release matrices at lower polymer contents with minimal risk of dose dumping.

Monitoring the Dissolution Mechanisms of Amorphous Bicalutamide Solid Dispersions via Real-Time Raman Mapping.

Real-time in situ Raman mapping has been employed to monitor, during dissolution, the crystallization transitions of amorphous bicalutamide formulated as a molecular dispersion in a copovidone VA64 matrix. The dissolution performance was also investigated using the rotating disc dissolution rate methodology, which allows simultaneous determination of the dissolution rate of both active ingredient and polymer. The dissolution behavior of two bicalutamide:copovidone VA64 dispersion formulations, containing 5% (w/w) and 50% (w/w) bicalutamide, respectively, was investigated, with the aim of exploring the effect of increasing the bicalutamide loading on the dissolution performance. Spatially time-resolved Raman maps generated using multivariate curve resolution indicated the simultaneous transformation of amorphous bicalutamide present in the 50% drug-loaded extrudate into metastable polymorphic form II and low-energy polymorphic form I. Fitting a kinetic model and spatially correlating the data extracted from the Raman maps also allowed us to understand the re-crystallization mechanisms by which the low-energy form I appears. Form I was shown to crystallize mainly directly from the amorphous solid dispersion, with crystallization from the metastable form II being a minor contribution.

High throughput screening for biomaterials discovery.

Using microarray technologies thousands of biomedical materials can be screened in a rapid, parallel and cost effective fashion to identify the optimum candidate that fulfils a specific biomedical application. High throughput surface characterization (HTSC) of printed microarrays has played a key role in the discovery and development of biomedical materials. This review focuses on the production and HTSC of microarrays, their application in specific biomedical fields and a future perspective on the development of this technology.

Real time Raman imaging to understand dissolution performance of amorphous solid dispersions.

We have employed for the first time Raman spectroscopic imaging along with multi-variate curve resolution (MCR) analysis to investigate in real time and in-situ the dissolution mechanisms that underpin amorphous solid dispersions, with data being collected directly from the dosage form itself. We have also employed a novel rotating disk dissolution rate (RDDR) methodology to track, through the use of high-performance liquid chromatography (HPLC), the dissolution trends of both drug and polymer simultaneously in multi-component systems. Two formulations of poorly water-soluble felodipine in a polymeric matrix of copovidone VA64 which have different drug loadings of 5% and 50% w/w were used as models with the aim of studying the effects of increasing the amount of active ingredient on the dissolution performance. It was found that felodipine and copovidone in the 5% dispersion dissolve with the same dissolution rate and that no Raman spectral changes accompanied the dissolution, indicating that the two components dissolve as single entity, whose behaviour is dominated by water-soluble copovidone. For the 50% drug-loaded dispersion, partial RDDR values of both felodipine and copovidone were found to be extremely low. MCR Raman maps along with classical Raman/X-ray powder diffraction (XRPD) characterisation revealed that after an initial loss of copovidone from the extrudate the drug re-crystallises, pointing to a release dynamics dependent on the low water solubility and high hydrophobicity of felodipine. Raman imaging revealed different rates of transition from amorphous to crystalline felodipine at different locations within the dosage form.

Desktop 3D printing of controlled release pharmaceutical bilayer tablets.

Three dimensional (3D) printing was used as a novel medicine formulation technique for production of viable tablets capable of satisfying regulatory tests and matching the release of standard commercial tablets. Hydroxypropyl methylcellulose (HPMC 2208) (Methocel™ K100M Premium) and poly(acrylic acid) (PAA) (Carbopol(®) 974P NF) were used as a hydrophilic matrix for a sustained release (SR) layer. Hypromellose(®) (HPMC 2910) was used as a binder while microcrystalline cellulose (MCC) (Pharmacel(®) 102) and sodium starch glycolate (SSG) (Primojel(®)) were used as disintegrants for an immediate release (IR) layer. Commercial guaifenesin bi-layer tablets (GBT) were used as a model drug (Mucinex(®)) for this study. There was a favourable comparison of release of the active guaifenesin from the printed hydrophilic matrix compared with the commercially available GBT. The printed formulations were also evaluated for physical and mechanical properties such as weight variation, friability, hardness and thickness as a comparison to the commercial tablet and were within acceptable range as defined by the international standards stated in the United States Pharmacopoeia (USP). All formulations (standard tablets and 3D printed tablets) showed Korsmeyer-Peppas n values between 0.27 and 0.44 which indicates Fickian diffusion drug release through a hydrated HPMC gel layer.

Quantification of pharmaceuticals via transmission Raman spectroscopy: data sub-selection.

We report the first systematic characterisation of data sub-selection with multivariate analysis to be applied to either TRS or the low-wavenumber Raman region. A model pharmaceutical formulation comprising two polymorphs mixed in the range of 1-99% is investigated. For data sub-selection, sparse partial least squares is for the first time applied to TRS data and compared with principal component analysis. It is found that low-wavenumber data (50-340 cm(-1)) are demonstrably superior for quantitative modelling than data in the more conventional mid-wavenumber range (340-2000 cm(-1)). Our results point the way to enhanced quantitative analytical capabilities for TRS, with potential application areas including pharmaceuticals, security and process-analytical technology, by combining data sub-selection with low-wavenumber-capable optics.

A kinetic and mechanistic study into the formation of the Cu-Cr layered double hydroxide.

The formation of the layered double hydroxide [Cu2Cr(OH)6]Cl·yH2O from the reaction between CuO and aqueous CrCl3·6H2O was explored using synchrotron X-ray diffraction and ex situ analyses. The use of hard X-rays permitted time-resolved in situ studies to be performed as the reaction proceeded under a range of conditions. Additional information was obtained from ex situ experiments in which aliquots of the reaction mixture were removed, quenched, and subsequently analysed by laboratory X-ray diffraction, IR, UV-visible, and atomic emission spectroscopies. On the basis of these data, it is proposed that the reaction involves three steps. First, the solid CuO starting material is hydrolysed to give Cu(OH)2 chains, releasing Cu(2+) ions into solution. The Cu hydroxide chains subsequently condense with aqueous Cr(3+) species, Cl(-) ions and water molecules to give a hydrated form of the LDH. This material then extrudes some water to form a phase with a reduced interlayer spacing.

Curcumin-containing chitosan nanoparticles as a potential mucoadhesive delivery system to the colon.

In the present study, we investigate the mucoadhesive characteristics and release of the anticancer agent curcumin, contained in chitosan nanoparticles (CS-NPs). Such a system has potential therapeutic benefits in the treatment of colon cancer through prolonged retention and delivery. The CS-NPs were ionically gelled with tripolyphosphate (TPP) and registered an isoelectric pH of 6.2 (z-average diameter of 214 nm ± 1.0 nm). pH variations around the isoelectric point caused a reduction in CS-NPs electrical charge which correspondingly increased the z-average due to agglomeration. Curcumin release from CS-NPs was slowest at chitosan to TPP weight ratio of 3:1, with a significant retention (36%) at the end of 6 h. Adsorption isotherms of mucin on CS-NPs fitted both the Freundlich and Langmuir models, suggesting a monolayer-limited adsorption on heterogeneous sites with varied affinities. Encapsulated curcumin exerted an influence on the adsorption of mucin due to H-bonding as well as π-π interactions between the phenolic moieties of curcumin and mucin.