The effect of temperature and moisture on the amorphous-to-crystalline transformation of stavudine

Engineering Alginate-Based Dry Powder Microparticles to a Size Suitable for the Direct Pulmonary Delivery of Antibiotics

The inhaled route is regarded as one of the most promising strategies as a treatment against pulmonary infections. However, the delivery of drugs in a dry powder form remains challenging. In this work, we have used alginate to form microparticles containing an antibiotic model (colistin sulfate). The alginate microparticles were generated by atomization technique, and they were characterized by antimicrobial in vitro studies against Pseudomonas aeruginosa. Optimization of different parameters allowed us to obtain microparticles as a dry powder with a mean size (Feret diameter) of 4.45 ± 1.40 µm and drug loading of 8.5 ± 1.50%. The process developed was able to concentrate most of the colistin deposits on the surface of the microparticles, which could be observed by SEM and a Dual-Beam microscope. This produces a fast in vitro release of the drug, with a 100% release achieved in 4 h. Physicochemical characterization using the FTIR, EDX and PXRD techniques revealed information about the change that occurs from the amorphous to a crystalline form of colistin. Finally, the cytotoxicity of microparticles was tested using lung cell lines (A549 and Calu-3). Results of the study showed that alginate microparticles were able to inhibit bacterial growth while displaying non-toxicity toward lung cells.

Amorphous Drug-Polymer Salts

Amorphous formulations provide a general approach to improving the solubility and bioavailability of drugs. Amorphous medicines for global health should resist crystallization under the stressful tropical conditions (high temperature and humidity) and often require high drug loading. We discuss the recent progress in employing drug–polymer salts to meet these goals. Through local salt formation, an ultra-thin polyelectrolyte coating can form on the surface of amorphous drugs, immobilizing interfacial molecules and inhibiting fast crystal growth at the surface. The coated particles show improved wetting and dissolution. By forming an amorphous drug–polymer salt throughout the bulk, stability can be vastly enhanced against crystallization under tropical conditions without sacrificing the dissolution rate. Examples of these approaches are given, along with suggestions for future work.

Co-amorphous formation of piroxicam-citric acid to generate supersaturation and improve skin permeation

The objective of this study was to prepare a co-amorphous formulation of piroxicam (PIR), a non-steroidal anti-inflammatory drug, and citric acid (CA), and evaluate its skin permeation ability. A spray-drying method was employed to prepare the co-amorphous formulation and its physical properties were characterized. X-ray powder diffraction and thermal analysis confirmed a homogeneous amorphous state, and the infrared spectra revealed intermolecular interactions between PIR and CA, suggesting formation of a co-amorphous formulation of PIR and CA. The PIR-CA co-amorphous formulation exhibited no crystallization for 60 days at 4/25/40°C with silica gel. The PIR-CA co-amorphous formulation increased the solubility of PIR in polyethylene glycol 400 compared with that of the pure drug, and physical mixture (PM) of PIR and CA, confirming a supersaturated state in the formulation. The PIR-CA co-amorphous formulation demonstrated higher skin permeation than PIR alone or PM of PIR and CA, and the flux value was consistent with the degree of saturation. Thus, the increase in the skin permeation of PIR from the PIR-CA co-amorphous formulation directly depended on the increased thermodynamic activity by supersaturation in the absence of interactions between the drug and co-former in the vehicle.

Disintegration mediated controlled release supersaturating solid dispersion formulation of an insoluble drug: design, development, optimization, and in vitro evaluation

The objective of this study was to develop a solid dispersion based controlled release system for drug substances that are poorly soluble in water. A wax-based disintegration mediated controlled release system was designed based on the fact that an amorphous drug can crystallize out from hydrophilic matrices. For this study, cilostazol (CIL) was selected as the model drug, as it exhibits poor aqueous solubility. An amorphous solid dispersion was prepared to assist the drug to attain a supersaturated state. Povidone was used as carrier for solid dispersion (spray drying technique), hydrogenated vegetable oil (HVO) as wax matrix former, and sodium carboxymethyl cellulose (NaCMC) as a disintegrant. The extreme vertices mixture design (EVMD) was applied to optimize the designed and developed composition. The optimized formulation provided a dissolution pattern which was equivalent to the predicted curve, ascertaining that the optimal formulation could be accomplished with EVMD. The release profile of CIL was described by the Higuchi's model better than zero-order, first-order, and Hixson-Crowell's model, which indicated that the supersaturation state of CIL dominated to allow drug release by diffusion rather than disintegration regulated release as is generally observed by Hixson-Crowell's model. The optimized composition was evaluated for disintegration, dissolution, XRD, and stability studies. It was found that the amorphous state as well as the dissolution profile of CIL was maintained under the accelerated conditions of 40°C/75% RH for 6 months.

Evaluation of different screening methods to understand the dissolution behaviors of amorphous solid dispersions

OBJECTIVE

The objectives of the current study were to understand the dissolution behaviors of amorphous solid dispersions (ASD) using different screening methods and their correlation to the dissolution of formulated products.

MATERIALS AND METHODS

A poorly soluble compound, compound E, was used as a model compound. ASDs were prepared with HPMC, Kollidon VA64 and Eudragit EPO using hot-melt extrusion. Different techniques including precipitation, powder, capsule and compact dissolution and the dissolution of formulated products were conducted in USP simulated gastric fluid using a USP II dissolution apparatus.

RESULTS AND DISCUSSIONS

It was found that a precipitation study could generally predict powder, capsule and compact dissolution. Yet, it was recommended to run the dissolution at a higher paddle speed or for a longer duration to improve the predictability. It was also recommended to run powder, capsule and compact dissolution at both slow and high speeds to gain insights into wetting, dispersion and the dissolution of a system. Sometimes, capsule or compact dissolution could not be predicted by precipitation or powder dissolution due to plug formation. In this case, properly designed dosage forms were needed to break up this plug to optimize the dissolution profiles. On the contrary, formulations and dissolution conditions would have minimal effects on the dissolution profiles of a fast-dissolving solid dispersion.

CONCLUSIONS

Different techniques are available to select the right polymers to optimize dissolution behaviors. However, it is important to understand the merits and limitations of each technique in order to optimize the formulations for amorphous solid dispersions.

Physicochemical properties of amorphous roxithromycin prepared by quench cooling of the melt or desolvation of a chloroform solvate

Roxithromycin is a poorly soluble antibacterial drug. The aim of this study was to prepare and characterize an amorphous form of roxithromycin. The amorphous form was prepared by desolvation of its chloroform solvate, and by quench cooling a melt of the crystalline monohydrated solid. The X-ray powder diffraction pattern of the desolvated chloroform solvate was indistinguishable from that of the glass prepared by melting, which indicated that it was amorphous. The roxithromycin glass was determined to be a fragile glass, but due to its high Kauzmann temperature (approximately 8°C), it should remain fairly stable upon refrigeration or even at room temperature. It was also determined that this glass remains stable in the presence of moisture with no indication of crystallization.

Evaluation of amorphous solid dispersion properties using thermal analysis techniques

Amorphous solid dispersions are an increasingly important formulation approach to improve the dissolution rate and apparent solubility of poorly water soluble compounds. Due to their complex physicochemical properties, there is a need for multi-faceted analytical methods to enable comprehensive characterization, and thermal techniques are widely employed for this purpose. Key parameters of interest that can influence product performance include the glass transition temperature (T(g)), molecular mobility of the drug, miscibility between the drug and excipients, and the rate and extent of drug crystallization. It is important to evaluate the type of information pertaining to the aforementioned properties that can be extracted from thermal analytical measurements, in addition to considering any inherent assumptions or limitations of the various analytical approaches. Although differential scanning calorimetry (DSC) is the most widely used thermal analytical technique applied to the characterization of amorphous solid dispersions, there are many established and emerging techniques which have been shown to provide useful information. Comprehensive characterization of fundamental material descriptors will ultimately lead to the formulation of more robust solid dispersion products.

Influence of microenvironment pH, humidity, and temperature on the stability of polymorphic and amorphous forms of clopidogrel bisulfate

The effect of microenvironment pH, humidity, and temperature was evaluated on the stability of polymorphic and amorphous forms of clopidogrel bisulfate, when present alone or in combinations. Oxalic acid and sodium carbonate were used as solid stressors to create acidic and alkaline pH, respectively. The samples without and with stressors were subjected for 3 months to (1) 0% RH, 25% RH, 75% RH, and 85% RH at 40 degrees C and also to (2) 60 degrees C, 80 degrees C, and 100 degrees C at 0% RH. In case of solid samples without stressors, the mixture of polymorphic and amorphous forms showed more degradation than the individual forms above critical relative humidity (85% RH). Similar higher degradation was observed between 75% RH and 85% RH in case of acid-stressed samples. In alkaline microenvironment, all the samples showed identical decomposition attributed to conversion of bisulfate salt to free base. Thermal studies indicated that polymorphic forms of clopidogrel bisulfate and also its glassy amorphous form were highly resistant to temperature, whereas the rubbery state of the drug degraded significantly at temperatures of > or =80 degrees C.