The evaluation of some pharmaceutically acceptable excipients as permeation enhancers for amoxicillin.

The aim of the present study was to evaluate different pharmaceutically acceptable excipients as permeation enhancers for a low permeability drug, amoxicillin. As a model for the intestinal epithelium excised rat jejunum, mounted in side-by-side diffusion cells, was used. Amoxicillin was actively transported across the intestine in the serosal-to-mucosal direction, but only if glucose was present at the mucosal side. This effect of glucose was abolished by a multridrug resistance associated protein (MRP) inhibitor benzbromarone (0.04 mM), but not by verapamil (0.2 mM). Among the tested pharmaceutically acceptable excipients only sodium lauryl sulfate (0.2 mg/ml) increased the permeability of amoxicillin in the mucosal-to-serosal direction, which was accompanying with the abolishment of the secretory oriented transport of amoxicillin. Other excipients (0.07 2mg/ml Pluronic F68, 0.2 mg/ml Lutrol F127, 0.2 mg/ml Cremophor EL or 0.2 mg/ml Carbopol 934) have no influence on the permeability of amoxicillin. The effect of sodium lauryl sulfate on the active secretion of amoxicillin was mainly attributed to the reversible cellular ATP depletion. We concluded that sodium lauryl sulfate can be considered as a relatively safe permeation enhancer for amoxicillin in drug delivery systems intended to improve oral bioavailability of this drug.

Erythropoietin unfolding: thermodynamics and its correlation with structural features.

Human erythropoietin (EPO) is a glycoprotein hormone considered to be the principal regulator of red blood cell formation. Although its recombinant version (rEPO) has been widely used for treatment of various anemias and its biological effects are relatively well-known, we know little about its biophysical properties and their relation to its structure. To gain a fuller understanding of the structural and functional properties of rEPO on the molecular level we followed its thermal and urea-induced unfolding at different pH (3.1-9.4) and urea concentrations (0-8 M) using spectropolarimetry, UV absorption, intrinsic emission fluorescence, and differential scanning calorimetry. Our results show that under a variety of conditions rEPO undergoes thermal or urea-induced denaturation that may be considered as a reversible two-state process characterized by unusually high (thermal) or moderate (urea-induced) extent of the residual structure. The highest thermal stability of the protein observed in aqueous solutions at physiological pH appears to be due to the largest difference in the extent of structure in the denatured and native state at this pH. The comparison between experimentally determined energetics of rEPO denaturation and its structure-based calculations indicates that the parametrization of thermodynamic quantities in terms of changes in solvent accessible nonpolar and polar surface areas resulting from protein unfolding can be successfully used provided that these changes are estimated from combination of experimentally determined deltaC(o)p and deltaH(o) values and not calculated from the structure of the protein's folded and assumingly fully unfolded state.

Silica coatings on clarithromycin.

Pre-crystallized clarithromycin (6-O-methylerythromycin A) particles were coated with silica from the tetraethyl orthosilicate (TEOS)-ethanol-aqueous ammonia system. The coatings had a typical thickness of 100-150 nm and presented about 15 wt.% of the silica-drug composite material. The properties of the coatings depended on reactant concentration, temperature and mixing rate and, in particular, on the presence of a cationic surfactant (cetylpyridinium chloride). In the presence of cetylpyridinium chloride the silica coatings slightly decreased the rate of pure clarithromycin dissolution.