Phase Diagrams of Polymer-Dispersed Liquid Crystal Systems of Itraconazole/Component Immiscibility Induced by Molecular Anisotropy

Liquid crystalline (LC) materials and their nonmedical applications have been known for decades, especially in the production of displays; however, the pharmaceutical implications of the LC state are inadequately appreciated, and the misunderstanding of experimental data is leading to possible errors, especially in relation to the physical stability of medicines. The aim of this work was to study LC phases of itraconazole (ITZ), an azole antifungal active molecule, and for the first time, to generate full thermodynamic phase diagrams for ITZ/polymer systems, taking into account isotropic and anisotropic phases that this drug can form. It was found that supercooled ITZ does not form an amorphous but a vitrified smectic (vSm) phase with a glass transition temperature of 59.35 °C (determined using a 10 °C/min heating rate), as is evident from X-ray diffraction and thermomicroscopic (PLM) experiments. Two endothermic LC events with the onset temperature values for a smectic to nematic transition of 73.2 ± 0.4 °C and a nematic to isotropic transformation at 90.4 ± 0.35 °C and enthalpies of transition of 416 ± 34 J/mol and 842 ± 10 J/mol, respectively, were recorded. For the binary supercooled mixtures, PLM and differential scanning calorimetry showed a phase separation with birefringent vSm persistent over a wide polymer range, as noticed especially for the hypromellose acetate succinate (HAS) systems. Both, smectic and nematic, phases were detected for the supercooled ITZ/HAS and ITZ/methacrylic acid-ethyl acrylate copolymer (EUD) mixtures, while geometric restrictions inhibited the smectic formation in the ITZ/poly(acrylic acid) (CAR) systems. The Flory-Huggins lattice theory coupled with the Maier-Saupe-McMillan approach to model anisotropic ordering of molecules was successfully utilized to create phase diagrams for all ITZ/polymer mixtures. It was concluded that in a supercooled ITR/polymer mix, if ITZ is present in a LC phase, immiscibility as a result of molecule anisotropy is afforded. This study shows that the LC nature of ITZ cannot be disregarded when designing stable formulations containing this molecule.

Amorphous Polymeric Drug Salts as Ionic Solid Dispersion Forms of Ciprofloxacin

Ciprofloxacin (CIP) is a poorly soluble drug that also displays poor permeability. Attempts to improve the solubility of this drug to date have largely focused on the formation of crystalline salts and metal complexes. The aim of this study was to prepare amorphous solid dispersions (ASDs) by ball milling CIP with various polymers. Following examination of their solid state characteristics and physical stability, the solubility advantage of these ASDs was studied, and their permeability was investigated via parallel artificial membrane permeability assay (PAMPA). Finally, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ASDs were compared to those of CIP. It was discovered that acidic polymers, such as Eudragit L100, Eudragit L100-55, Carbopol, and HPMCAS, were necessary for the amorphization of CIP. In each case, the positively charged secondary amine of CIP was found to interact with carboxylate groups in the polymers, forming amorphous polymeric drug salts. Although the ASDs began to crystallize within days under accelerated stability conditions, they remained fully X-ray amorphous following exposure to 90% RH at 25 °C, and demonstrated higher than predicted glass transition temperatures. The solubility of CIP in water and simulated intestinal fluid was also increased by all of the ASDs studied. Unlike a number of other solubility enhancing formulations, the ASDs did not decrease the permeability of the drug. Similarly, no decrease in antibiotic efficacy was observed, and significant improvements in the MIC and MBC of CIP were obtained with ASDs containing HPMCAS-LG and HPMCAS-MG. Therefore, ASDs may be a viable alternative for formulating CIP with improved solubility, bioavailability, and antimicrobial activity.

Molecular Dynamics and Physical Stability of Amorphous Nimesulide Drug and Its Binary Drug-Polymer Systems

In this article we study the effectiveness of three well-known polymers: inulin, Soluplus, and PVP in stabilizing the amorphous form of nimesulide (NMS) drug. The recrystallization tendency of pure drug as well as measured drug-polymer systems were examined at isothermal conditions by broadband dielectric spectroscopy (BDS) and at nonisothermal conditions by differential scanning calorimetry (DSC). Our investigation has shown that the crystallization half-life time of pure NMS at 328 K is equal to 33 min. We found that this time can be prolonged to 40 years after adding 20% w/w PVP to NMS. This polymer proved to be the best NMS stabilizer, while the worst stabilization effect was exhibited by inulin. Additionally, our DSC, BDS, and FTIR studies indicate that for suppression of NMS recrystallization in the NMS-PVP system, the two mechanisms are responsible: the polymeric steric hindrances and the antiplastization effect exerted by the excipient.

Cocrystal habit engineering to improve drug dissolution and alter derived powder properties

Objectives

Cocrystallization of sulfadimidine (SDM) with suitable coformers, such as 4-aminosalicylic acid (4-ASA), combined with changes in the crystal habit can favourably alter its physicochemical properties. The aim of this work was to engineer SDM : 4-ASA cocrystals with different habits to investigate the effect on dissolution, and the derived powder properties of flow and compaction.

Methods

Cocrystals were prepared in a 1 : 1 molar ratio by solvent evaporation using ethanol (habit I) or acetone (habit II), solvent evaporation followed by grinding (habit III) and spray drying (habit IV).

Key findings

Powder X-ray diffraction showed Bragg peak position was the same in all the solid products. The peak intensity varied, indicating different preferred crystal orientation confirmed by SEM micrographs: large prismatic crystals (habit I), large plate-like crystals (habit II), small cube-like crystals (habit III) and microspheres (habit IV). The habit III exhibited the fasted dissolution rate; however, it underwent a polymorphic transition during dissolution. Habits I and IV exhibited the highest Carr's compressibility index, indicating poor flowability. However, habits II and III demonstrated improved flow. Spray drying resulted in cocrystals with improved compaction properties.

Conclusions

Even for cocrystals with poor pharmaceutical characteristics, a habit can be engineered to alter the dissolution, flowability and compaction behaviour.

Molecular origin of enhanced proton conductivity in anhydrous ionic systems

Ionic systems with enhanced proton conductivity are widely viewed as promising electrolytes in fuel cells and batteries. Nevertheless, a major challenge toward their commercial applications is determination of the factors controlling the fast proton hopping in anhydrous conditions. To address this issue, we have studied novel proton-conducting materials formed via a chemical reaction of lidocaine base with a series of acids characterized by a various number of proton-active sites. From ambient and high pressure experimental data, we have found that there are fundamental differences in the conducting properties of the examined salts. On the other hand, DFT calculations revealed that the internal proton hopping within the cation structure strongly affects the pathways of mobility of the charge carrier. These findings offer a fresh look on the Grotthuss-type mechanism in protic ionic glasses as well as provide new ideas for the design of anhydrous materials with exceptionally high proton conductivity.

Dry powders for oral inhalation free of lactose carrier particles

Dry powder inhaler (DPI) products have traditionally comprised a simple formulation of micronised drug mixed with a carrier excipient, typically lactose monohydrate. The presence of the carrier is aimed at overcoming issues of poor flowability and dispersibility, associated with the cohesive nature of small, micronised active pharmaceutical ingredient (API) particles. Both the powder blend and the DPI device must be carefully designed so as to ensure detachment of the micronised drug from the carrier excipient on inhalation. Over the last two decades there has been a significant body of research undertaken on the design of carrier-free formulations for DPI products. Many of these formulations are based on sophisticated particle engineering techniques; a common aim in formulation design of carrier-free products being to reduce the intrinsic cohesion of the particles, while maximising dispersion and delivery from the inhaler. In tandem with the development of alternative formulations has been the development of devices designed to ensure the efficient delivery and dispersion of carrier-free powder on inhalation. In this review we examine approaches to both the powder formulation and inhaler design for carrier-free DPI products.

Heat induced evaporative antisolvent nanoprecipitation (HIEAN) of itraconazole

Itraconazole (ITR) is an antifungal drug with a limited bioavailability due to its poor aqueous solubility. In this study, ITR was used to investigate the impact of nanonisation and solid state change on drug's apparent solubility and dissolution. A bottom up approach to the production of amorphous ITR nanoparticles (NPs), composed of 100% drug, with a particle diameter below 250 nm, using heat induced evaporative antisolvent nanoprecipitation (HIEAN) from acetone was developed. The NPs demonstrated improved solubility and dissolution in simulated gastro-intestinal conditions when compared to amorphous ITR microparticles. The incorporation of polyethylene glycol (PEG) or its methoxylated derivative (MPEG) as a stabiliser enabled the production of smaller NPs with narrower particle size distribution and enhanced apparent solubility. MPEG stabilised NPs gave the greatest ITR supersaturation levels (up to 11.6±0.5 μg/ml) in simulated gastric fluids. The stabilising polymer was in an amorphous state. Dynamic vapour sorption data indicated no solid state changes in NP samples with water vapour at 25 °C, while crystallisation was apparent at 50 °C. HIEAN proved to be an efficient method of production of amorphous ITR NPs, with or without addition of a polymeric stabiliser, with enhanced pharmaceutical properties.

Observation of highly decoupled conductivity in protic ionic conductors

Using dielectric spectroscopy, we report the observation of highly decoupled conductivity in a newly synthesized protic ionic conductor, lidocaine di-(dihydrogen phosphate).

Exploring the assembly process and properties of novel crosslinker-free hyaluronate-based polyelectrolyte complex nanocarriers

The aim of this work was to study the formulation of pharmaceutically relevant polyelectrolyte complex nanoparticles (NPs) composed of hyaluronic acid (HA) and chitosan (CS) containing no crosslinkers. The influence of polymer mixing ratio, concentration and molecular weight as well as the type of counterion in chitosan salt on properties of the resulting NPs was examined. Formulations and their components were studied by laser light scattering, viscosity, infrared spectroscopy and microscopy. Physical stability, isoelectric points and cytotoxicity of selected NPs were determined. By appropriate modification of HA molecular weight, stable and non-sedimenting NPs were successfully formed. Sonication was found to be an effective method to reduce the molecular weight of HA from 2882±25 to 176±4 kDa with no chemical changes in the HA structure observed. High molecular weight CS formed micron-sized entities at all compositions investigated. Positively and negatively charged NPs were obtained depending on the mixing ratio of the polymers, with CS glutamate NPs yielding more negatively charged particles compared to CS chloride NPs. The smallest NPs (149±11 nm) were formed using HA with molecular weight of 176 kDa. Cytotoxicity of NPs was dependent on environmental pH but HA was found to exert cytoprotective effects on Caco-2 cells.

Impact of process variables on the micromeritic and physicochemical properties of spray-dried porous microparticles, part I: introduction of a new morphology classification system

Objectives

This work investigated the impact of spray drying variables such as feed concentration, solvent composition and the drying mode, on the micromeritic properties of chlorothiazide sodium (CTZNa) and chlorothiazide potassium (CTZK).

Methods

Microparticles were prepared by spray drying and characterised using thermal analysis, helium pycnometry, laser diffraction, specific surface area analysis and scanning electron microscopy.

Key findings

Microparticles produced under different process conditions presented several types of morphology. To systematise the description of morphology of microparticles, a novel morphology classification system was introduced. The shape of the microparticles was described as spherical (1) or irregular (2) and the surface was classified as smooth (A) or crumpled (B). Three classes of morphology of microparticles were discerned visually: class I, non-porous; classes II and III, comprising differing types of porosity characteristics. The interior was categorised as solid/continuous (α), hollow (β), unknown (γ) and hollow with microparticulate content (δ). Nanoporous microparticles of CTZNa and CTZK, produced without recirculation of the drying gas, had the largest specific surface area of 72.3 and 90.2 m2/g, respectively, and presented morphology of class 1BIIIα.

Conclusions

Alteration of spray drying process variables, particularly solvent composition and feed concentration can have a significant effect on the morphology of spray dried microparticulate products. Morphology of spray dried particles may be usefully described using the morphology classification system.

Impact of process variables on the micromeritic and physicochemical properties of spray-dried microparticles – Part II. Physicochemical characterisation of spray-dried materials

Objectives

In this work we investigated the residual organic solvent content and physicochemical properties of spray-dried chlorothiazide sodium (CTZNa) and potassium (CTZK) salts.

Methods

The powders were characterised by thermal, X-ray diffraction, infrared and dynamic vapour sorption (DVS) analyses. Solvent levels were investigated by Karl–Fischer titration and gas chromatography.

Key findings

Spray-drying from water, methanol (MeOH) and mixes of MeOH and butyl acetate (BA) resulted in amorphous microparticles. The glass transition temperatures of CTZNa and CTZK were ∼192 and ∼159°C, respectively. These materials retained their amorphous nature when stored at 25°C in dry conditions for at least 6 months with no chemical decomposition observed. DVS determined the critical relative humidity of recrystallisation of CTZNa and CTZK to be 57% RH and 58% RH, respectively. The inlet temperature dependant oxidation of MeOH to formaldehyde was observed; the formaldehyde was seen to deposit within the amorphous matrix of spray-dried product. Spray-drying in the open blowing mode coupled with secondary drying resulted in a three-fold reduction in residual BA (below pharmacopoeial permitted daily exposure limit) compared to spray-drying in the closed mode.

Conclusions

Experiments showed that recirculation of recovered drying gas increases the risk of deposition of residual solvents in the spray-dried product.