Supercritical fluid crystallization of griseofulvin: crystal habit modification with a selective growth inhibitor

Heterogeneous Nucleation in Protein Crystallization

Protein crystallization was first discovered in the nineteenth century and has been studied for nearly 200 years. Protein crystallization technology has recently been widely used in many fields, such as drug purification and protein structure analysis. The key to successful crystallization of proteins is the nucleation in the protein solution, which can be influenced by many factors, such as the precipitating agent, temperature, solution concentration, pH, etc., among which the role of the precipitating agent is extremely important. In this regard, we summarize the nucleation theory of protein crystallization, including classical nucleation theory, two-step nucleation theory, and heterogeneous nucleation theory. We focus on a variety of efficient heterogeneous nucleating agents and crystallization methods as well. The application of protein crystals in crystallography and biopharmaceutical fields is further discussed. Finally, the bottleneck of protein crystallization and the prospect of future technology development are reviewed.

Polymorphism of griseofulvin: concomitant crystallization from the melt and a single crystal structure of a metastable polymorph with anomalously large thermal expansion

Single crystal structure of the metastable polymorph of griseofulvin with anomalously large thermal expansion.

Liquisolid technique to enhance and to sustain griseofulvin dissolution: effect of choice of non-volatile liquid vehicles

Liquisolid systems were originally designed to enhance dissolution of hydrophobic drugs. Recently, the same technique was explored to control drug release via hydrophobic carriers. This work aimed to study the effects of different liquid vehicles on release characteristics of griseofulvin as a model hydrophobic drug. Fast dissolution tablets were prepared using three different non-ionic surfactants namely Cremophor(®)EL, Synperonic(®)PE/L61 and Capryol™ 90, on the contrary Kollicoat(®)SR 30D was used for production of grieseofulvin sustained release formulations. Avicel(®) PH102 and Cab-O-Sil(®) M5 were used as carrier and coat materials, respectively. The effect of formulation parameters, such as drug concentration and carrier to coat ratio, on enhancing drug dissolution was explored. Drug concentrations of 20% and 40% (w/w), and R-values (carrier to coat ratio) of 10 and 20 were used. The mathematical model was utilized to formulate liquisolid powder systems. All fast release liquisolid formulations showed higher percentage drug dissolution efficiency (%DE) than conventional directly compacted tablets. Cremophor(®)EL showed the best dissolution enhancement with %DE of about 90%, compared to only 23% for conventional tablets; DSC data suggested loss of griseofulvin crystallinity and thermal behavior. Kollicoat(®) SR 30D retarded the drug release even in the presence of hydrophilic carrier; DSC data suggested that only small fraction of the drug was present in the molecular state within the system. The used liquisolid vehicles showed promise to enhance and to control (depend on the choice of the liquid vehicle) the release of griseofulvin from liquisolid compacts.

Fast-dissolving microparticles fail to show improved oral bioavailability

Oral dosage forms are the preferred means of delivering drugs for systemic absorption. However, development problems occur for drugs with poor water solubility and/or gastrointestinal permeability. It is generally believed that the in-vivo bioavailability of poorly water-soluble drugs from Class II of the Biopharmaceutics Classification System can be improved by increasing the dissolution rate. We have attempted to increase the in-vivo oral bioavailability of a model Class II drug (griseofulvin) by preparing rapidly-dissolving particles. The solvent-diffusion method was used to prepare particles with hydrophilic surfactants (Brij 76/Tween 80 surfactant blend) and in-vivo studies were conducted in rats. The griseofulvin particles produced were bipyramidal in habit with a particle size of 2.18 ± 0.12 mm; they contained crystalline drug and a relatively large proportion (12% w/w) of hydrophilic surfactant. The latter and the small particle size ensured rapid particle dispersion and dissolution in-vitro. Thus, within 30 min of the in-vitro dissolution test, the bipyramidal particles had released ∼70% of drug compared with ∼10% from the starting material (particle size 12.61 ± 1.11 μm). However, the rapid and increased drug dissolution in-vitro was not translated to rapid and enhanced absorption in-vivo, and the oral bioavailability of the model drug was found to be the same from the control and from the bipyramidal particles. The poor in-vivo performance of the bipyramidal particles showed that although the dissolution rate of a Class II drug is thought to be a good indicator of its in-vivo bioavailability, this is not always the case.

Development and physicochemical evaluation of pharmacosomes of diclofenac

Pharmacosomes are amphiphilic lipid vesicular systems that have shown their potential in improving the bioavailability of poorly water soluble as well as poorly lipophilic drugs. Diclofenac is a poorly water soluble drug and also causes gastrointestinal toxicity. To improve the water solublity of diclofenac, its pharmacosomes (phospholipid complex) have been prepared and evaluated for physicochemical analysis. Diclofenac was complexed with phosphatidylcholine (80%) in equimolar ratio, in the presence of dichloromethane, by the conventional solvent evaporation technique. Pharmacosomes thus prepared were evaluated for drug solubility, drug content, surface morphology (by scanning electron microscopy), phase transition behaviour (by differential scanning calorimetry), crystallinity (by X-ray powder diffraction) and in vitro dissolution. Pharmacosomes of diclofenac were found to be irregular or disc shaped with rough surfaces in SEM. Drug content was found to be 96.2 +/- 1.1%. DSC thermograms and XRPD data confirmed the formation of the phospholipid complex. Water solubility of the prepared complex was found to be 22.1 microg mL-1 as compared to 10.5 microg mL-1 of diclofenac. This improvement in water solubility in prepared pharmacosomes may result in improved dissolution and lower gastrointestinal toxicity. Pharmacosomes showed 87.8% while the free diclofenac acid showed a total of only 60.4% drug release at the end of 10 h of dissolution study.

Supercritical carbon dioxide processing of active pharmaceutical ingredients for polymorphic control and for complex formation

Supercritical fluid technique have been exploited in extraction, separation and crystallization processes. In the field of pharmaceutics, supercritical carbon dioxide (scCO(2)) has been used for the purpose of micronization, polymorphic control, and preparation of solid dispersion and complexes. Particle design of active pharmaceutical ingredients is important to make the solid dosage forms with suitable physicochemical properties. Control of the characteristic properties of particles, such as size, shape, crystal structure and morphology is required to optimize the formulation. For solubility enhancement of poorly water-soluble drugs, preparation of the solid dispersion or the complexation with proper drugs or excipients should be a promising approach. This review focuses on aspects of polymorphic control and complexation behavior of active pharmaceutical ingredients by scCO(2) processing.

Comparative Physicochemical Characterization of Phospholipids Complex of Puerarin Formulated by Conventional and Supercritical Methods

PURPOSE

The aim of this work was to compare the physicochemical characteristics of the phospholipids complex of puerarin (Pur) prepared by traditional methods (solvent evaporation, freeze-drying and micronization) and a supercritical fluid (SCF) technology. The physicochemical properties of the pure drug and the corresponding products prepared by two different SCF methods were also compared.

METHODS

Solid-state characterization of particles included differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), solubility, dissolution rate and scanning electron microscopy (SEM) examinations. Besides puerarin phospholipids complex (PPC) by four different methods, the solid-state properties of unprocessed, gas antisolvent (GAS) crystallized and solution enhanced dispersion by supercritical fluid (SEDS) precipitated puerarin samples were also compared. Crystallinity was assessed using DSC and XRPD. Drug-phospholipids interactions were characterized using Fourier transform infrared spectroscopy (FTIR). SEM was used to determine any morphological changes. Pharmaceutical performance was assessed in dissolution rate and solubility tests.

RESULT

The results of the physical characterization attested a substantial correspondence of the solid state of the drug before and after treatment with GAS technique, whereas a pronounced change in size and morphology of the drug crystals was noticed. The GAS-processed puerarin exhibited a better crystal shape confirmed by DSC, XRPD and IR. Polymorphic change of puerarin during SEDS coupled with the dramatic reduction of the dimensions determined a remarkable enhancement of its solubility and in vitro dissolution rate. Phospholipids complex prepared using supercritical fluid technology showed similar properties of physical state, thermal stability and molecular interaction with phospholipids (PC) to those of corresponding systems prepared by other three conventional methods namely solvent evaporation, freeze-drying and micronization as proved by XRPD, DSC, and FTIR. The best dissolution rate was obtained by SEDS-prepared complex, while the highest solubility was obtained for solvent evaporation method.

CONCLUSION

Supercritical fluid technology for the preparation of puerarin and its phospholipids complex has been proven to have significant advantages over the solvent evaporation technique and other conventional methods.

Polymorphism and solvatomorphism 2005

Papers and patents that deal with polymorphism (crystal systems for which a substance can exist in structures characterized by different unit cells, but where each of the forms consists of exactly the same elemental composition) and solvatomorphism (systems where the crystal structures of the substance are defined by different unit cells, but where these unit cells differ in their elemental composition through the inclusion of one or molecules of solvent) have been summarized in an annual review. The works cited in this review were published during 2005, and were drawn primarily from the major physical, crystallographic, and pharmaceutical journals. The review is divided into sections that cover articles of general interest, computational and theoretical studies, preparative and isolation methods, structural characterization and properties of polymorphic and solvatomorphic systems, studies of phase transformations, effects associated with secondary processing, and United States patents issued during 2005.