Characterization of a quaternary liquid system improving the bioavailability of poorly water soluble drugs

Monodisperse Micro-Oil Droplets Stabilized by Polymerizable Phospholipid Coatings as Potential Drug Carriers

There is a critical need to formulate stable micron-sized oil droplets as hydrophobic drug carriers for efficient drug encapsulation, long-term storage, and sustained drug release. Microfluidic methods were developed to maximize the stability of micron-sized, oil-in-water (o/w) emulsions for potential use in drug delivery, using doxorubicin-loaded triacetin oil as a model hydrophobic drug formulation. Initial experiments examined multiple flow conditions for the dispersed (oil) and continuous (liposome aqueous) phases in a microfluidic device to establish the parameters that influenced droplet size. These data were fit to a mathematical model from the literature and indicate that the droplet sizes formed are controlled by the ratio of flow rates and the height of the device channel, rather than the orifice size. Next, we investigated effects of o/w emulsion production methods on the stability of the droplets. The stability of o/w emulsion produced by microfluidic flow-focusing techniques was found to be much greater (5 h vs 1 h) than for emulsions produced by mechanical agitation (vortexing). The increased droplet stability was attributed to the uniform size and lipid distribution of droplets generated by flow-focusing. In contrast, vortexed populations consisted of a wide size distribution that resulted in a higher prevalence of Ostwald ripening. Finally, the effects of shell polymerization on stability were investigated by comparing oil droplets encapsulated by a photopolymerizable diacetylene lipid shell to those with a nonpolymerizable lipid shell. Shell polymerization was found to significantly enhance stability against dissolution for flow-focused oil droplets but did not significantly affect the stability of vortexed droplets. Overall, results of these experiments show that flow-focusing is a promising technique for generating tunable, stable, monodisperse oil droplet emulsions, with potential applications for controlled delivery of hydrophobic drug formulations.

Preparation and evaluation of nimesulide-loaded ethylcellulose and methylcellulose nanoparticles and microparticles for oral delivery

The present study was designed to assess and compare with a range of surfactant-coated, nimesulide-free, and nimesulide-loaded ethylcellulose/methylcellulose (EC/MC) nanoparticles that were prepared by varying drug concentration (ED/MD), polymer concentration (EP/MP), and surfactant concentration (ES/MS). EC/MC nanoparticles prepared by desolvation method produced discrete particles and they were characterized by SEM, AFM, and FTIR studies. The particles mean size diameter (nm) ranged from 244 to 1056 nm and 1065 to 1710 nm for EC and MC nanoparticles, respectively. Studies on drug: polymer ratio showed a linear relationship between drug concentration and percentage of loading in nanoparticles. The encapsulation efficiency decreased with the increase of nimesulide concentration with respect to polymer concentration. Encapsulation efficiency of drug-loaded nanoparticles was varied between 32.8% and 64.9%. The in vitro release of drug-loaded nanoparticles was found to be a first order. This was significantly increased in EC nanoparticles (95.50%) in comparison with MC nanoparticles (95.12%) after 12 h in 24 h long study. Nimesulide release from EC nanoparticles was much slower at slightly alkaline pH 7.4. The in vitro hemolysis tests of nanoparticles were carried out to ascertain the hemocompatibility and shown to be insignificant for EC nanoparticles. In comparison, ES4 from EC formulations with nimesulide was found to be promising with slow and sustained drug release.

Current Perspectives of Solubilization: Potential for Improved Bioavailability

This review focuses on the recent techniques of solubilization for the attainment of effective absorption and improved bioavailability. Solubilization may be affected due to cosolvent water interaction or altered crystal structure by cosolvent addition. Micellar solubilization could be affected by both ionic strength and pH. Addition of cosolvents to the surfactant solutions offers only a small advantage because of the decrease in the solubilization capacity of the micelles. Polymorphism is known to influence dissolution and bioavailability of the drugs. Molecular modeling study of cyclodextrin inclusion complexations can predict the inclusion modes, stoichiometry of the complex, and the relative complexing efficiency of cyclodextrins with various drug molecules.

Comparison of the effect of tromethamine and polyvinylpyrrolidone on dissolution properties and analgesic effect of nimesulide

The solubilizing and absorption enhancer properties towards nimesulide (ND) of tromethamine (Tris) and polyvinylpyrrolidone (PVP) have been investigated. Solid binary systems were prepared at various drug-polymer ratios by mixing or coprecipitation, characterized by differential scanning calorimetry, X-ray diffractometry, and Fourier transform infrared spectroscopy, and tested for dissolution behavior. Both carriers improved drug dissolution and their performance depended on concentration of the hydrophilic carrier in coprecipitates. Tris was more effective than PVP, despite the amorphizing power of PVP as revealed by solid state analyses. Complete drug amorphiztion was attained at 1:3 (wt/wt) drug:PVP, 25% (wt/wt) ND in PVP. According to thermal behavior of ND and Tris, ND-Tris systems present a eutectic behavior. The eutectic composition was 30% ND-70% Tris at approximately 129 degrees C. Amorphous ND-PVP and eutectic ND-Tris mixtures showed an improvement of 5.55 and 6.6 times of drug dissolution efficiency, respectively. In vivo experiments in mice demonstrated that administration of 50 mg/kg of drug coprecipitated with PVP or Tris resulted, respectively, in a 50% and 94% reduction of acetic acid-induced writhings in comparison with pure drug, which, instead, was statistically ineffective as compared with the control group. Moreover, the eutectic mixture of ND-Tris demonstrated antiwrithing potency 1.88 times higher than amorphous ND-PVP coprecipitate. Thus, the solubilizing power, dissolution-enhancing effect, and analgesic effect enhancer ability toward the drug make Tris particularly suitable for developing a reduced-dose, fast-release solid oral dosage form of nimesulide.

In vitro Nimesulide Absorption from Different Formulations

In light of improving the bioavailability of poorly water-soluble drugs, this work focused on the comparison among different nimesulide formulations resorting to in vitro absorption experiments through everted rat intestine. The performance of a nimesulide ethanol-triacetin solution, an activated system made up by cogrinding nimesulide/polyvinylpyrrolidone and simple solid nimesulide were compared with that of a reference nimesulide solution. Although ethanol-triacetin solution showed a better performance than the solid nimesulide because wettability problems connected with nimesulide were completely zeroed, the activated system showed a better performance than the reference solution one. This was due to the fact that the activated system allowed to overcome both the wettability and solubility problems connected with nimesulide. Moreover, as proved by intestinal pictures taken before and after permeation experiments, we observed the adhesion of polymeric particles to intestinal villi, this giving origin to a thin layer, surrounding the intestine, characterized by a nimesulide concentration higher than that in the release environment bulk. A proper mathematical model, based on Fick's second law, was developed to model drug absorption in the case of solution and activated system. In this manner, we could calculate nimesulide permeability through the intestinal wall, and we could better define the nature of the above-mentioned thin layer surrounding the intestine. Finally, the mathematical model was used to verify the theoretical correctness of the widely employed technique consisting in data correction for dilution when sample withdrawal and replacement were needed to measure drug concentration in the receiver environment.