Surfactant and temperature effects on paraben transport through silicone membranes

Mechanistic Insight in Permeability through Different Membranes in the Presence of Pharmaceutical Excipients: A Case of Model Hydrophobic Carbamazepine

The present study reports the effects of two pharmaceutical excipients of differing natures-non-ionic surfactant pluronic F127 (F127) and anionic sulfobutylether-β-cyclodextrin (SBE-β-CD)-on the permeation of the model compound, carbamazepine (CBZ). The permeability coefficients of CBZ at three concentrations of the excipients were measured through two different artificial barriers: hydrophilic cellulose membrane (RC) and lipophilic polydimethylsiloxane-polycarbonate membrane (PDS). The equilibrium solubility of CBZ in F127 and SBE-β-CD solutions was determined. The micellization, complexation, and aggregation tendencies were investigated. Systemically increasing the solubility and the reduction of permeation upon the excipients' concentration growth was revealed. The quantitative evaluation of the permeability tendencies was carried out using a Pratio parameter, a quasi-equilibrium mathematical mass transport model, and a correction of permeability coefficients for the free drug concentration ("true" permeability values). The results revealed the mutual influence of the excipient properties and the membrane nature on the permeability variations.

Determining suitable surfactant concentration ranges to avoid protein unfolding in pharmaceutical formulations using UV analysis

Protein stability is fundamental to maintain pharmaceutical efficacy in the nascent field of biologics. One particular property that is essential for therapeutic effect is retention of the folded 3-dimensional conformation, i.e. once unfolding has occurred the biologic is often rendered inactive. In this work we propose a modified form of a recently published UV spectroscopic method that identifies protein unfolding. In this study we determine concentration limits to avoid protein unfolding of two model surfactants, namely polysorbate 20 and polysorbate 80, by correlating surfactant concentration with percentage 'unfolded' for three model proteins. For each scenario two distinct regions were observed, firstly surfactant concentrations at which no unfolding had occurred, followed by a second region whereby unfolding steadily increased with surfactant concentration. In general for the combinations analysed in this study, this second region began to appear around ten times below the critical micellar concentration of each surfactant, regardless of the protein or polysorbate chosen. It is therefore proposed that this adapted method could be used by researchers in the early stages of formulation development as a convenient and simple screening tool to confirm the 'onset of unfolding' concentration for protein-surfactant formulations, thus helping to optimise surfactant concentration selection in pharmaceutical formulations to maintain the benefits of surfactants yet avoid inadvertent unfolding.

The effect of the presence of biosurfactant on the permeation of pharmaceutical compounds through silicone membrane

The permeation of ten model drugs through silicone membrane was analysed to investigate the effect of the presence of a biosurfactant obtained from corn steep liquor. The ten selected pharmaceutical compounds were chosen to include a diverse range of physicochemical properties, such as variable hydrophobicities, pKa's, molecular masses and degrees of ionisation. When compared with compound permeation alone, the additional inclusion of biosurfactant in the donor phase altered the rate and extent of permeation. It significantly enhanced permeation for five of the compounds, whereas it decreased permeation for four of the compounds and remained approximately the same for the tenth compound. These effects were observed at both biosurfactant concentrations considered, namely 0.005 mg/mL, i.e. below the critical micellar concentration (CMC) and 0.500 mg/mL, i.e. above the CMC of the biosurfactant. Upon analysing permeation change with respect to physicochemical properties of the compounds, it was determined that compounds with a relative molecular mass below 200 resulted in an increase in permeation with biosurfactant present, and those above 200 resulted in a decrease in permeation with biosurfactant present. This effect was therefore attributed to the formation of a drug-biosurfactant interaction that enhanced permeation of smaller compounds, yet retarded permeation for those with a higher molecular mass. These in vitro findings can be considered an indication of potential novel formulation options that incorporate biosurfactant to create transdermal products that have bespoke permeation profiles.

Effect of plasma surface treatment of poly(dimethylsiloxane) on the permeation of pharmaceutical compounds

This paper addresses the modification of poly(dimethylsiloxane), i.e. PDMS, using plasma surface treatment and a novel application of the membrane created. A set of model compounds were analysed to determine their permeation through PDMS, both with and without plasma treatment. It was found that plasma treatment reduced permeation for the majority of compounds but had little effect on some compounds, such as caffeine, with results indicating that polarity plays an important role in permeation, as is seen in human skin. Most importantly, a direct correlation was observed between plasma-modified permeation data and literature data through calculation of membrane permeability (K_p) values suggesting plasma-modified silicone membrane (PMSM) could be considered as a suitable in vivo replacement to predict clinical skin permeation.

Ionisation effects on the permeation of pharmaceutical compounds through silicone membrane

Silicone membrane is frequently used as an in vitro skin mimic whereby experiments incorporate a range of buffered media which may vary in pH. As a consequence of such variability in pH there is a corresponding variability in the degree of ionisation which in turn, could influence permeation through the mainly hydrophobic-rich membrane structure. This study reports the effect of pH on the permeation of five model compounds (benzoic acid, benzotriazole, ibuprofen, ketoprofen and lidocaine). For the five compounds analysed, each at three distinct percentages of ionisation, it was found that the greater extent of permeation was always for the more 'neutral', i.e. more greatly unionised, species rather than the anionic or cationic species. These findings fit with the theory that the hydrophobic membrane encourages permeation of 'lipid-like' structures, i.e. the more unionised form of compounds. However, results obtained with an Inverse Gas Chromatography Surface Energy Analyser (iGC SEA) indicate the membrane surface to be an electron dense environment. In the knowledge that unionised forms of compounds permeate (rather than the charged species) this negatively charged surface was not anticipated, i.e. the basic membrane surface did not appear to affect permeation.

Novel olefinic-centered macroacyclic compounds involving tetrasubstituted 4-hydroxybenzoic acid fragments: synthesis, structural characterization and comparison of experimental and computational results

Dialkyl 4,4'-(2-(1,3-bis(4-(alkoxycarbonyl)phenoxy)propan-2-ylidene)propane-1,3-diyl)bis (oxy)dibenzoate 6a,b were synthesized through the reaction of ethene-1,1,2,2,-tetra-yl-tetra methylene tetra bromide 1 with methyl 4-hydroxy benzoate or ethyl 4-hydroxy benzoate 2a,b. In addition, compounds 6a,b were obtained by using the esterification reaction from the reaction compound 5 with methyl and ethyl alcohol in high yields. Compound 4 was synthesized from the reaction of ethene-1,1,2,2,-tetra-yl-tetra methylene tetra bromide 1 with 4-hydroxy benzonitrile 3. The structures of the novel synthesized compounds were confirmed by IR, (1)H NMR, (13)C NMR, COSY, elemental analysis, and mass spectral data. Compound 6b, C42H44O12, was also characterized with additional analysis such as UV-vis, and X-ray spectral techniques. The electronic structure of compound 6b was studied by DFT level 6-31G∗(d,p) using X-ray crystallographic data. The results obtained from this study are consistent with the X-ray data. In order to understand the electronic transitions of the compound 6b, time dependent density functional theory (TD-DFT) calculations were carried out. TD-DFT studies showed that the low-energy excitations are consistent with the experimental results.