Formulation and evaluation of a vitamin C multiple emulsion.

Multiple phase emulsions are increasingly used as alternatives to simple emulsions in personal care products. One of the major advantages of these emulsions over simple emulsions is slow and controlled release of their ingredients. Other favorite cosmetic characteristics of multiple emulsions include occlusivity (in O/W/O emulsions), esthetics and consumer acceptance. Vitamin C (ascorbic acid) has been widely used in formulations of skin care products. Due to its effects on collagen biosynthesis, it is considered as moisturizing and anti-aging active ingredient. Instability problems such as oxidation susceptibility have made incorporating vitamin C in topical formulations a challenging issue. The O/W/O emulsions have been formulated using two-step procedure, to investigate vitamin C stability and its release profile. By using different surfactant types and ratios, volume ratio of phases, multiple emulsions containing vitamin C were prepared. Different parameters and formulation factors such as temperature of phases, duration and speed of mixing were evaluated. Based on our results, more stable emulsions were prepared from non-ionic siliconized surfactants, sorbitan derivatives and co-surfactants such as polyglyceryl derivatives. Physical stability was determined by microscopic examination, centrifugation and incubating emulsions in different temperatures. Vitamin C in vitro release studies from O/W and O/W/O emulsions were conducted using Franz diffusion cell (at room temperature) and UV spectrophotometry. The results showed that in the first four-hour period, about 14% of vitamin C released from O/W/O emulsions. It appears that in multiple emulsions the profile of release follows zero-order kinetics. Our data indicate that incorporating vitamin C in multiple emulsions significantly increased its stability possibly attributed to the formation of reverse micelles of surfactants (and/or co-surfactants), which entrapped vitamin C inside the micelles surrounded by hydrophilic heads of surfactant. Moreover, vitamin C was released from multiple emulsions in a zero order slow and controlled release manner.

A rapid and selective LC method for simultaneous determination of cyclosporin a and its major metabolite (AM1) in human serum at room temperature.

A simple and highly selective isocratic reverse-phase high performance liquid chromatography (RP-LC) method at room temperature is developed in order to determination of Cyclosporine A (CyA) and its major metabolite (AM1) in serum samples of kidney transplanted patients. The method uses a phenyl column stationary phase, acetonitrile-water-methanol 47:50:3 as mobile phase and 215 nm detector wavelength, at room temperature. The solid phase extraction procedure using cyano disposable extraction column was carried out to separtate the CyA and AM1 with recovery 99+/-6 and 98+/-10, respectively. A linear correlation was found at the range of 40-1000 ng ml(-1) for CyA and 25-500 ng ml(-1) for AM1. The average intra and inter-day variations were 5.03 and 7.89% for CyA, 5.92 and 8.12% for AM1, respectively. The detection limit of 20 ng ml(-1) was found for CyA and 12.5 ng ml(-1) for AM1. Also, the clinical application of the method using serum concentration against time profile from kidney transplantated patients is reported.

Inhibition of serum angiotensin-converting enzyme in rabbits after intravenous administration of enalaprilat-loaded intact erythrocytes.

Encapsulation of drugs in intact erythrocytes, because of the profound characteristics of these natural microspheres, has gained considerable attention in recent years. In this study, the inhibition time courses of serum angiotensin-converting enzyme (ACE) activity after intravenous administration of enalaprilat encapsulated in intact erythrocytes was evaluated and compared with free drug, in a rabbit model. Three groups of animals each received free drug, drug-loaded erythrocytes or sham-encapsulated erythrocytes. Serum ACE activity was determined in each case using the synthetic substrate hippuryl-histidyl-leucine and quantitation of the hippuric acid released by a developed and validated HPLC method. The serum ACE inhibition profiles in the three groups showed that the encapsulated drug inhibited the serum ACE more slowly, more efficiently, over a considerably longer time and in a more reproducible manner, than the free drug or sham-encapsulated erythrocytes. We conclude that the erythrocytes can serve as efficacious slow-release drug carriers for enalaprilat in circulation.

A simple HPLC method for quantitation of enalaprilat.

A reversed-phase high performance liquid chromatography (HPLC) method with UV-detection has been developed for the determination of enalaprilat. The method produced linear response over the wide concentration range of 1-200 microg/ml, with an average accuracy of 97.35 +/- 4.93%, as well as average intra- and iter-day variations of 3.72 and 5.18%, respectively. The limits of detection and quantitation of the method were 0.125 and 0.5 microg/ml, respectively. The method was selective with respect to resolution of the peaks of enalaprilat and enalapril maleate.

In vitro characterization of human intact erythrocytes loaded by enalaprilat.

In vitro characteristics of the human erythrocytes loaded by enalaprilat have been evaluated. Erythrocytes obtained from a healthy volunteer were loaded by enalaprilat using the hypotonic preswelling method, and the loading parameters, drug-release kinetics, hematological indices, particle size distribution, scanning electron microscopy view, osmotic and turbulence fragilities, and deformability of the resulting carrier cells were determined along with the sham encapsulated and unloaded cells. Carrier erythrocytes, having acceptable loading parameters, released their drug content according to zero-order kinetics. Mean corpuscular hemoglobin and mean corpuscular hemoglobin content values of the cells decreased, particle size dispersion increased, the cells transformed to cup-form, the erythrocytes became more fragile against osmotic pressure and turbulent flow, and, finally, the deformability of the cells decreased significantly upon drug loading.

Evaluation of hypotonic preswelling method for encapsulation of enalaprilat in intact human erythrocytes.

The hypotonic preswelling method for encapsulation of drugs in intact human erythrocytes was evaluated using enalaprilat as a model peptide-like drug. Several process variables, including volume, concentration, pH, and method of addition of drug solution, type of erythrocyte-suspending medium, temperature, initial packed density of erythrocytes, and individual process steps, were exploited with respect to their effects on the loading parameters (i.e., loaded amount, efficiency of entrapment, and cell recovery). In addition, the probable mechanism by which the erythrocytes were loaded by enalaprilat at the point of lysis was shown to be a simple concentration gradient-based diffusion through membrane openings occurring on hemolysis. Finally, the adopted method was validated, and the results showed a considerable degree of reproducibility and recovery for the entire loading procedure.

An isocratic high-performance liquid chromatographic system for simultaneous determination of theophylline and its major metabolites in human urine.

A simple and highly selective isocratic high-performance liquid chromatography method is presented for the simultaneous determination of theophylline and its major metabolites in human urine using beta-hydroxyethyl theophylline as an internal standard. The method utilizes direct injection of diluted urine samples followed by separation and quantitation by reversed-phase isocratic elution and ultraviolet detection. The assay is accurate and reproducible with a sensitivity of 1 microgram ml-1 for theophylline and 0.5 micrograms ml-1 for its metabolites. The assay was employed for the analysis of theophylline and its major metabolites in urine following the oral administration of theophylline to four healthy volunteers.

Blood to plasma ratio of mefloquine: interpretation and pharmacokinetic implications.

The blood to plasma ratio of the antimalarial mefloquine has been reported to be close to 1, while other reports indicate extensive accumulation in erythrocytes. This apparent contradiction has been resolved by a quantitative examination of the compensating effects of plasma protein binding of mefloquine which almost exactly matches the extent of mefloquine accumulation in erythrocytes. The observed blood to plasma ratio of about 1 arises as the result of a balance between extensive red cell uptake and extensive plasma protein binding. Some pharmacokinetic implications of the distribution of mefloquine within blood are outlined.