Development of a rapid, reliable and quantitative method--"SPOTi" for testing antifungal efficacy.

A reference method for the antimicrobial susceptibility testing of common fungal pathogens such as dermatophytes, is currently lacking. In this study, we report the successful adaptation of solid agar-based spot culture growth inhibition assay (SPOTi) for dermatophytes, currently being used as a gold-standard in the anti-tubercular drug discovery field. The fungal-SPOTi assay correlated with the disc-diffusion method, and is validated using mycelial plugs. We propose the fungal-SPOTi as a high-throughput alternative to the disc-diffusion and broth micro-dilution anti-fungal assays to screen novel anti-fungals.

Mechanisms of burst release from pH-responsive polymeric microparticles.

OBJECTIVES: Microencapsulation of drugs into preformed polymers is commonly achieved through solvent evaporation techniques or spray drying. We compared these encapsulation methods in terms of controlled drug release properties of prepared microparticles and investigated the underlying mechanisms responsible for the 'burst release' effect. METHODS: Using two different pH-responsive polymers with a dissolution threshold of pH 6 (Eudragit L100 and AQOAT AS-MG), hydrocortisone, a model hydrophobic drug, was incorporated into microparticles below and above its solubility within the polymer matrix. KEY FINDINGS: Although, spray drying was an attractive approach due to rapid particle production and relatively low solvent waste, the oil-in-oil microencapsulation method was superior in terms of controlled drug release properties from the microparticles. Slow solvent evaporation during the oil-in-oil emulsification process allowed adequate time for drug and polymer redistribution in the microparticles and reduced uncontrolled drug burst release. Electron microscopy showed that this slower manufacturing procedure generated nonporous particles whereas thermal analysis and X-ray diffractometry showed that drug loading above the solubility limit of the drug in the polymer generated excess crystalline drug on the surface of the particles. Raman spectral mapping illustrated that drug was homogeneously distributed as a solid solution in the particles when loaded below saturation in the polymer with consequently minimal burst release. CONCLUSIONS: Both the manufacturing method (which influenced particle porosity and density) and drug:polymer compatibility and loading (which affected drug form and distribution) were responsible for burst release seen from our particles.

Using pH abnormalities in diseased skin to trigger and target topical therapy.

PURPOSE: The pH discrepancy between healthy and atopic dermatitis skin was identified as a site-specific trigger for delivering hydrocortisone from microcapsules. METHODS: Using Eudragit L100, a pH-responsive polymer which dissolves at pH 6, hydrocortisone-loaded microparticles were produced by oil-in-oil microencapsulation or spray drying. Release and permeation of hydrocortisone from microparticles alone or in gels was assessed, and preliminary stability data was determined. RESULTS: Drug release from microparticles was pH-dependent, though the particles produced by spray drying also gave significant non-pH-dependent burst release, resulting from their porous nature or from drug enrichment on the surface of these particles. This pH-responsive release was maintained upon incorporation of the oil-in-oil microparticles into Carbopol- and HPMC-based gel formulations. In vitro studies showed 4- to 5-fold higher drug permeation through porcine skin from the gels at pH 7 compared to pH 5. CONCLUSIONS: Permeation studies showed that the oil-in-oil-generated particles deliver essentially no drug at normal (intact) skin pH (5.0-5.5) but that delivery can be triggered and targeted to atopic dermatitis skin where the pH is elevated. The incorporation of these microparticles into Carbopol- and HPMC-based aqueous gel formulations demonstrated good stability and pH-responsive permeation into porcine skin.

Production of pH-responsive microparticles by spray drying: investigation of experimental parameter effects on morphological and release properties.

During spray drying, emphasis is placed on process optimisation to generate favourable particle morphological and flow properties. The effect of the initial feed solution composition on the drug release from the prepared microparticles (MPs) is rarely considered. We investigated the effects of solvent composition, feed solution concentration and drug-loading on sodium salicylate, hydrocortisone and triamcinolone release from spray-dried Eudragit L100 MPs. Eudragit L100 is a pH-responsive polymer whose dissolution threshold is pH 6 so dissolution testing of the prepared MPs at pH 5 and 1.2 illustrated non-polymer controlled burst release. Increasing the water content of the initial ethanolic feed solution significantly reduced hydrocortisone burst release at pH 5, as did reducing the feed solution concentration. These findings caution that changes in feed solution concentration or solvent composition not only affect particles' morphological characteristics but can also negatively alter their drug release properties. This work also illustrate that drug-free MPs can have different morphological properties to drug-loaded MPs. Therefore, process optimisation needs to be carried out using drug-loaded systems. Depending on the physicochemical properties of the encapsulated active pharmaceutical ingredient (API), drug-loading can affect the polymer solubility in the initial feed solution with consequent impact on MPs morphological and release properties.