The release and analgesic activities of morphine and its ester prodrug, morphine propionate, formulated by water-in-oil nanoemulsions

Effect of Salt on the Formation and Stability of Water-in-Oil Pickering Nanoemulsions Stabilized by Diblock Copolymer Nanoparticles

Sterically stabilized diblock copolymer nanoparticles are prepared in n-dodecane using polymerization-induced self-assembly. Precursor Pickering macroemulsions are then prepared by the addition of water followed by high-shear homogenization. In the absence of any salt, high-pressure microfluidization of such precursor emulsions leads to the formation of relatively large aqueous droplets with DLS measurements indicating a mean diameter of more than 600 nm. However, systemically increasing the salt concentration produces significantly finer droplets after microfluidization, until a limiting diameter of around 250 nm is obtained at 0.11 M NaCl. The mean size of these aqueous droplets can also be tuned by systematically varying the nanoparticle concentration, applied pressure, and the number of passes through the microfluidizer. The mean number of nanoparticles adsorbed onto each aqueous droplet and their packing efficiency are calculated. SAXS studies conducted on a Pickering nanoemulsion prepared using 0.11 M NaCl confirms that the aqueous droplets are coated with a loosely packed monolayer of nanoparticles. The effect of varying the NaCl concentration within the droplets on their initial rate of Ostwald ripening is investigated using DLS. Finally, the long-term stability of these water-in-oil Pickering nanoemulsions is assessed using analytical centrifugation. The rate of droplet ripening can be substantially reduced by using 0.11 M NaCl instead of pure water. However, increasing the salt concentration up to 0.43 M provided no further improvement in the long-term stability of such nanoemulsions.

A diffusing wave spectroscopy study of pharmaceutical emulsions for physical stability assessment

Emulsions are broadly used in pharmaceutics either as intermediate products or as final dosage forms. Such disperse systems are only kinetically stabilized and therefore early detection of physical instability is highly desirable. This work employed diffusing wave spectroscopy (DWS) to study a series of model emulsions that were categorized, based on their composition, as either "simple" or "complex". DWS data were compared with results of droplet size imaging, apparent viscosity obtained by microfluidics, and near-infrared (NIR) analytical centrifugation. A mathematical model of the droplet mean square displacement (MSD) was modified by us regarding improved fitting of experimental data. Although the emulsions showed different types of instability like creaming and sedimentation, a good rank correlation was found between the DWS parameters and results from the comparative stability methods. Our findings indicate that DWS provides a highly attractive method for stability analysis of pharmaceutical emulsions because it requires only low sample volumes, is rapid and non-invasive. The proposed data modeling provides the means for a better understanding of emulsion microstructure that in turn will help designing quality into pharmaceutical dispersions.

Oil components modulate the skin delivery of 5-aminolevulinic acid and its ester prodrug from oil-in-water and water-in-oil nanoemulsions

The study evaluated the potential of nanoemulsions for the topical delivery of 5-aminolevulinic acid (ALA) and methyl ALA (mALA). The drugs were incorporated in oil-in-water (O/W) and water-in-oil (W/O) formulations obtained by using soybean oil or squalene as the oil phase. The droplet size, zeta potential, and environmental polarity of the nanocarriers were assessed as physicochemical properties. The O/W and W/O emulsions showed diameters of 216-256 and 18-125 nm, which, respectively, were within the range of submicron- and nano-sized dispersions. In vitro diffusion experiments using Franz-type cells and porcine skin were performed. Nude mice were used, and skin fluorescence derived from protoporphyrin IX was documented by confocal laser scanning microscopy (CLSM). The loading of ALA or mALA into the emulsions resulted in slower release across cellulose membranes. The release rate and skin flux of topical drug application were adjusted by changing the type of nanocarrier, the soybean oil O/W systems showing the highest skin permeation. This formulation increased ALA flux via porcine skin to 180 nmol/cm(2)/h, which was 2.6-fold that of the aqueous control. The CLSM results showed that soybean oil systems promoted mALA permeation to deeper layers of the skin from ∼100 μm to ∼140 μm, which would be beneficial for treating subepidermal and subcutaneous lesions. Drug permeation from W/O systems did not surpass that from the aqueous solution. An in vivo dermal irritation test indicated that the emulsions were safe for topical administration of ALA and mALA.

Permeation enhancer-containing water-in-oil nanoemulsions as carriers for intravesical cisplatin delivery

PURPOSE

In the present work, we developed water-in-oil (w/o) nanoemulsions for the intravesical administration of cisplatin.

METHODS

The nanoemulsions were made up of soybean oil as the oil phase and Span 80, Tween 80, or Brij 98 as the emulsifier system. alpha-Terpineol and oleic acid were incorporated as permeation enhancers. The physicochemical characteristics of droplet size, zeta potential, and viscosity were determined. Nanoemulsions were administered intravesically for 1 approximately 4 h to rats in vivo. Animals were subsequently sacrificed, and the bladders were harvested to examine drug accumulation and histology.

RESULTS

Ranges of the mean size and zeta potential were 30 approximately 90 nm and -3.4 to -9.3 mV, respectively. The addition of enhancers further reduced the size of the nanoemulsions. The viscosity of all systems exhibited Newtonian behavior. The cisplatin-loaded nanoemulsions were active against bladder cancer cells. The nanoemulsions with Brij 98 exhibited the complete inhibition of cell proliferation. The encapsulation of cisplatin and carboplatin, another derivative of cisplatin, in nanoemulsions resulted in slower and more-sustained release. The amount of drug which permeated into bladder tissues significantly increased when using carriers containing Brij 98, with the alpha-terpineol-containing formulation showing the best result. The nanoemulsion with alpha-terpineol prolonged the duration of higher drug accumulation to 3 approximately 4 h. At the later stage of administration (3 approximately 4 h), this system increased the bladder wall deposition of cisplatin and carboplatin by 2.4 approximately 3.3-fold compared to the control solution. Histological examination of the urothelium showed near-normal morphology in rats instilled with these nanoemulsions. alpha-Terpineol possibly caused slight desquamation of umbrella cells.

CONCLUSIONS

The nanoemulsions are feasible to load cisplatin for intravesical drug delivery.