Particle design of tolbutamide by the spherical crystallization technique. III. Micromeritic properties and dissolution rate of tolbutamide spherical agglomerates prepared by the quasi-emulsion solvent diffusion method and the solvent change method

Towards a better understanding of the role of stabilizers in QESD crystallizations

Quasi-emulsion solvent-diffusion crystallization (QESD) is a type of spherical crystallization which can be used as a particle design method to improve the flowability and micromeritic properties of drugs or excipients. Spherical particles are generated by dispersing a solvent phase in an antisolvent so that a transient emulsion is formed. Within the droplets the material can crystallize and agglomerate into spherical, hollow particles. Surfactants, such as surface-active polymers like hypromellose, are often required to stabilize the quasi-emulsion. To gain further understanding for the role of the stabilizer, a new screening-method was developed which compared different surface active polymers in solution at similar dynamic viscosities rather than at a set concentration. The dynamic viscosities of a low-viscosity grade hypromellose solution used in the previous publications describing the QESD crystallization of metformin hydrochloride by the authors was used as a target value. QESD crystallizations of metformin hydrochloride (MF) and celecoxib showed that the type of stabilizer and whether it is dissolved in the solvent or antisolvent has an effect on the agglomerates. For MF, the type of hypromellose used can have a significant influence on the properties of the agglomerates. More polymers could be used to stabilize the transient emulsion of celecoxib than previously found in literature. Furthermore, QESD crystallizations seem to be more robust when the stabilizer is dissolved in the antisolvent, however this can lead to a reduced drug load of the agglomerates.

Preparation of spherical agglomerates from potash alum

Spherical crystallization proved to be feasible for the preparation of spherical salt hydrate particles as core material for microencapsulation.

Improved dissolution and micromeritic properties of naproxen from spherical agglomerates: preparation, in vitro and in vivo characterization

Naproxen, an anti-inflammatory drug, exhibits poor aqueous solubility, which limits the pharmacological effects. The present work was carried out to study the effect of agglomeration on micromeritic properties and dissolution. Naproxen agglomerates were prepared by using a three solvents system composed of acetone (good solvent), water (non-solvent) and dichloromethane (bridging liquid). Differential Scanning Calorimetry (DSC) results showed no change in the drug after crystallization process. X-Ray Powder Diffraction (XRPD) studies showed the sharp peaks are present in the diffractograms of spherical agglomerates with minor reduction in height of the peaks. The residual solvents are largely below the tolerated limits in the agglomerates. Scanning Electronic Microscopy (SEM) studies showed that agglomerates were spherical in structure and formed by cluster of small crystals. The agglomerates exhibited improved solubility, dissolution rate and micromeritic properties compared to pure drug. Anti-inflammatory studies were conducted in Wistar strain male albino rats and naproxen agglomerates showed more significant activity than the pure drug.

Spherical crystallization of drugs

Spherical crystallization of drugs is the process of obtaining larger particles by agglomeration during crystallization. The most common techniques used to obtain such particles are spherical agglomeration and quasi-emulsion solvent diffusion. Ammonia diffusion systems and crystallo-co-agglomeration are extensions of these techniques. By controlling process parameters during crystallization, such as temperature, stirring rate, type and amount of solvents, or excipient selection, it is possible to control the formation of agglomerates and obtain spherical particles of the desired size, porosity, or hardness. Researchers have reported that the particles produced have improved micromeritic, physical, and mechanical properties, which make them suitable for direct compression. In some cases, when additional excipients are incorporated during spherical crystallization, biopharmaceutical parameters including the bioavailability of drugs can also be tailored.

Spherical crystals of celecoxib to improve solubility, dissolution rate and micromeritic properties

Celecoxib spherical agglomerates were prepared with polyvinylpyrrolidone (PVP) using acetone, water and chloroform as solvent, non-solvent and bridging liquid, respectively. The agglomerates were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopic studies and scanning electron microscopy (SEM). The IR spectroscopy and DSC results indicated the absence of any interactions between drug and additives. XRD studies showed a decrease in crystallinity in agglomerates. The crystals exhibited significantly improved micromeritic properties compared to pure drug. The loading efficiency (% or mg drug per 100 mg crystals) was in the range of 93.9 +/- 2.3 and 97.3 +/- 1.3% (n = 3) with all formulations. The aqueous solubility and dissolution rate of the drug from crystals was significantly (p < 0.05) increased (nearly two times). The solubility and in vitro drug release rates increased with an increase in PVP concentration (from 2.5 to 10%). The SEM studies showed that the crystal posseses a good spherical shape with smooth and regular surface.

Study of the preparation of sustained-release microspheres containing zedoary turmeric oil by the emulsion–solvent-diffusion method and evaluation of the self-emulsification and bioavailability of the oil

The purpose of this study was to design a sustained-release formulation of an oily drug. The sustained-release microspheres with self-emulsifying capability containing zedoary turmeric oil (ZTO) were prepared by the quasi-emulsion-solvent-diffusion method. The micromeritic properties, the efficiency of emulsification and the drug-release behavior of the resultant microspheres were investigated. The bioavailability of the microspheres was compared with conventional ZTO self-emulsifying formulations for oral administration using 12 healthy rabbits. An HPLC method was employed to determine the concentration of germacrone in plasma, which was used as an index of ZTO. Spherical and compacted microspheres with average diameters of 100-600 microm have been prepared, and their release behavior in distilled water containing 1.2% (w/v) of polysorbate-80 can be controlled by the ratio of polymer/Areosil200 in the microspheres. The resultant emulsions with mean droplet sizes of 200-500 nm are produced when the microspheres are immersed in phosphate buffer (pH 6.8) under gentle agitation. The stability and the droplet size of the resultant emulsions are also affected by the polymer/Areosil200 ratio in the formulation, while the amount of talc has a marked effect on the self-emulsifying rate. The plasma concentration-time profiles with improved sustained-release characteristics were achieved after oral administration of the microspheres with a bioavailability of 135.6% with respect to the conventional self-emulsifying formulation (a good strategy for improving the bioavailability of an oily drug). In conclusion, the sustained-release microspheres with self-emulsifying capability containing ZTO have an improved oral bioavailability. Our study offers an alternative method for designing sustained-release preparations of oily drugs.

A novel pH-dependent gradient-release delivery system for nitrendipine: I. Manufacturing, evaluation in vitro and bioavailability in healthy dogs

A novel pH-dependent gradient-release delivery system was developed by mixing three kinds of pH-dependent microspheres. Nitrendipine, a dihydropyridine calcium antagonist, was selected as the poorly water-soluble model drug. To obtain gradient-release of the active drug in the stomach, duodenum and lower segment of the small intestine, respectively, three kinds of pH-dependent polymers, i.e. Acrylic resins Eudragit E-100, Hydroxypropylmethylcellulose phthalate and Hydroxypropylmethylcellulose acetate succinate, were formulated to produce the microspheres, which dissolve at an acid condition, the pH of > or = 5.5 and > or = 6.5, respectively. The quasi-emulsion solvent diffusion method was employed in the manufacturing process for the microspheres. All three kinds of microspheres had a highly spherical shape and high incorporation efficiency (>91.0%). The particle sizes were mainly affected by the agitation speed and temperature of the manufacturing process. The results of X-ray diffraction suggested that nitrendipine in the microspheres was molecularly dispersed in an amorphous state. The drug dissolution behavior of the system under the simulated gastrointestinal pH conditions revealed obvious gradient-release characteristics. The dissolution profiles and content of the systems stored at a temperature of 40 degrees C and a relative humidity of 75% were unchanged during a 3-month period of accelerating storage conditions. The results of the bioavailability testing in six healthy dogs suggested that the pH-dependent gradient-release delivery system could improve efficiently the uptake of the poorly water-soluble drug and prolong the Tmax value in vivo.

Design of sustained-release nitrendipine microspheres having solid dispersion structure by quasi-emulsion solvent diffusion method

To improve the bioavailability of nitrendipine microspheres, a sustained-release microspheres having solid dispersion structure were prepared in one step. Two types of polymer, i.e. solid dispersing and sustained-release polymers, were employed to prepare the microspheres by the spherical crystallization technique, i.e. quasi-emulsion solvent diffusion method. The factors of effect on micromeritic properties and release profiles of the resultant microspheres were investigated. And the bioavailability of nitrendipine microspheres was evaluated in six healthy dogs. The results showed that the particle size of microspheres was determined mainly by the agitation speed. The dissolution rate of nitrendipine from microspheres was enhanced significantly with increasing the amount of dispersing agents, and sustained by adding retarding agents. The release rate of microspheres could be controlled as desired by adjusting the combination ratio of dispersing agents to retarding agents. The results of X-ray diffraction and differential scanning calorimetry analysis indicated that the crystalline form of nitrendipine was disordered, suggesting that nitrendipine was highly dispersed in microspheres, so as amorphous state. The release profiles and content of the microspheres stored at a temperature of 40 degrees C and a relative humidity of 75% were unchanged during 3 months of accelerating condition of storage. And the relative bioavailability of the sustained-release microspheres compared with the Baypress tablets and the conventional tablets was 107.78% and 309.82%. In conclusion, the sustained-release microspheres with solid dispersion structure improved the bioavailability of the water insoluble drug and prolonged the Tmax value.

Spherical crystallization of celecoxib

Celecoxib exhibits poor flow properties and compressibility. Spherical crystallization of celecoxib was carried out using the solvent change method. An acetone:dichloromethane (DCM):water system was used where DCM acted as a bridging liquid and acetone and water as good and bad solvent, respectively. Hydroxypropylmethylcellulose (HPMC) was used to impart strength and sphericity to the agglomerates. The effect of amount of bridging liquid and speed of agitation was studied using 3(2) factorial design. Primary properties of the agglomerates were evaluated by infrared spectroscopy, powder X-ray diffraction, and differential scanning calorimetry. The effect of variables on micromeritic, mechanical, compressional, and dissolution behavior was evaluated by response surface methodology. Particle size, bulk density, mean yield pressure (MYP), and drug release were found to be significantly affected by either of the two variables. Interaction of variables significantly affected the MYP.

Enhanced absorption of indomethacin after oral or rectal administration of a self-emulsifying system containing indomethacin to rats

A self-emulsifying system (SES), a mixture of an oil and a surfactant which forms an oil-in-water emulsion, is expected to improve the in vitro drug dissolution and enhance the in vivo drug absorption. In this study, a poorly water-soluble drug, indomethacin (IDM) was incorporated into the SES to increase bioavailability. The SES with 30% of Tween 85 and 70% of ethyl oleate, EO (w/w) was selected as an optimized formulation (high drug loading, low surfactant concentration, and small particle size). After an oral administration of the SES containing IDM and IDM suspension, (IDM was suspended in methyl cellulose), 22.5 mg/kg as IDM, to rats, the area under the plasma concentration-time curve from time zero to the last measured time in plasma, 12 h (AUC(0-12 h)) was significantly greater (57% increase) in the SES, suggesting that oral absorption of IDM increased significantly by the SES. After a rectal administration of gelatin hollow type suppositories, filled with the SES containing IDM and IDM powder physically mixed with the SES, 22. 5 mg/kg, to rats, the AUC(0-12 h) also increased significantly (41% increase) by the SES, suggesting that rectal absorption of IDM also increased significantly by the SES.

Effect of formulation variables on in vitro drug release and micromeritic properties of modified release ibuprofen microspheres

Modified release microspheres of the non-steroidal anti-inflammatory drug, ibuprofen, were formulated and prepared using the emulsion solvent diffusion technique. The contribution of various dispersed phase and continuous phase formulation factors on in vitro drug release and micromeritic characteristics of microspheres was examined. The results demonstrated that the use of Eudragit RS 100 and Eudragit RL 100 as embedding polymers modified the drug release properties as a function of polymer type and concentration. Eudragit RS 100 retarded ibuprofen release from the microspheres to a greater extent than Eudragit RL 100. The drug/polymer concentration of the dispersed phase influenced the particle size and drug release properties of the formed microspheres. It was found that the presence of emulsifier was essential for microsphere formation. Increasing the concentration of emulsifier, sucrose fatty acid ester F-70, decreased the particle size which contributed to increased drug release properties. Scanning electron microscopy revealed profound distortion in both the shape and surface morphology of the microspheres with the use of magnesium stearate as added emulsifier. The application of an additional Eudragit RS 100 coat onto formed microspheres using fluid bed technology was successful and modulated the drug release properties of the coated microspheres.

Mechanical properties of powders for compaction and tableting: an overview

This review provides an insight into mechanical properties that are critical to understanding powder processing for tableting. Various parameters that reflect these basic fundamental properties of powder and their evaluation by different techniques are described. Some recent examples in which these techniques are used in drug substance selection, formulation optimization or scale-up are also provided.