Release characteristics of anionic drug compounds from liquid crystalline gels

Physicochemical performances of indomethacin in cholesteryl cetyl carbonate liquid crystal as a transdermal dosage

A transdermal formulation of indomethacin (IMC) was developed by incorporation into cholesteryl cetyl carbonate (CCC). The liquid crystalline phase properties of the IMC-CCC mixture were detected by polarized light microscopy and differential scanning calorimetry. A low drug loading was obtained (1-5 %) similar to that used in conventional topical IMC in a clinical setting. A controlled release of IMC was found over 12 h. A low amount of IMC in 1 % IMC-CCC permeated the stratum corneum. Further formulation development has been carried out by the addition of lauryl alcohol into 5 % IMC-CCC mixture it was found that the permeation of IMC was significantly improved to 45 % within 24 h.

Hybrid Anion Exchange Hollow Fiber Membrane for Delivery of Ionic Drugs

Hybrid anion exchange hollow fiber membranes (HAEHFMs) based on bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) are proposed as potential drug carriers for four anionic model drugs, including the sodium salts of benzoate (NaBS), salicylate (NaSA), meta-amino salicylate (NaMAS), and loxoprofen (NaLS). The results of the static loading and release experiments suggest that electrostatic interaction, hydrogen bonding, and hydrophobic interaction are the main interaction patterns between the membrane and the drugs. And they are directly influenced by the external phase conditions and the drug physicochemical characteristics, such as structure, molecular weight, dissociation (pKa), and hydrogen bonding capability. Among the four different drugs, NaSA and NaMAS appear to be the most suitable for controlled release by the HAEHFM due to their excellent adsorption/release behaviors.

Effect of sodium diclofenac loads on mesophase components and structure

We studied the effect of a model electrolytic drug on intermolecular interactions, conformational changes, and phase transitions in structured discontinuous cubic QL lyotropic liquid crystals. These changes were due to competition with hydration of the lipid headgroups. Structural changes of the phase induced by solubilization loads of sodium diclofenac (Na-DFC) were investigated by directly observing the water, ethanol, and Na-DFC components of the resulting phases using 2H and 23Na NMR. Na-DFC interacted with the surfactant glycerol monoolein (GMO) at the interface while interfering with the mesophase curvature and also competed with hydration of the surfactant headgroups. Increasing quantities of solubilized Na-DFC promoted phase transitions from cubic phase (discontinuous (QL) and bicontinuous (Q)) into lamellar structures and subsequently into a disordered lamellar phase. Quadrupolar coupling of deuterated ethanol by 2H NMR showed that it is located near the headgroups of the lipid and apparently is hydrogen bonded to the GMO headgroups. A phase transition between two lamellar phases (L alpha to L alpha*) was seen by 23Na NMR of Na-DFC at a concentration where the characteristics of the drug change from kosmotropic to chaotropic. These findings show that loads of solubilized drug may affect the structure of its vehicle and, as a result, its transport across skin-blood barriers. The structural changes of the mesophase may also aid controlled drug delivery.

Multifunctional polyelectrolyte multilayer films: combining mechanical resistance, biodegradability, and bioactivity

Cross-linked polyelectrolyte multilayer films (CL PEM) have an increased rigidity and are mechanically more resistant than native (e.g., uncrosslinked) films. However, they are still biodegradable, which make them interesting candidates for biomedical applications. In this study, CL PEM films have been explored for their multifunctional properties as (i) mechanically resistant, (ii) biodegradable, and (iii) bioactive films. Toward this end, we investigated drug loading into CL chitosan/hyaluronan (CHI/HA) and poly(L-lysine)/hyaluronan (PLL/HA) films by simple diffusion of the drugs. Sodium diclofenac and paclitaxel were chosen as model drugs and were successfully loaded into the films. The effect of varying the number of layers in the (CHI/HA) films as well as the cross-linker concentration on diclofenac loading were studied. Diclofenac was released from the film in about 10 h. Paclitaxel was also found to diffuse within CL films. Its activity was maintained after loading in the CL films, and cellular viability could be reduced by about 55% over 3 days. Such a simple approach may be applied to other types of cross-linked films and to other drugs. These results prove that it is possible to design multifunctional multilayer films that combine mechanical resistance, biodegradability, and bioactivity properties into a single PEM architecture.

Release characteristics of anionic drug compounds from liquid crystalline gels

This paper investigates the release and transport of a range of anionic drugs from liquid crystalline gels using chemical and physical enhancement techniques. Previous papers [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels. I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236; Fitzpatrick, D., Corish, J., 2006. Release characteristics of anionic drug compounds from liquid crystalline gels. II. The effects of ion pairing and buffering on the passive delivery of anionic drugs across non rate-limiting membranes. Int. J. Pharm.] have reported on the passive release profiles and those resulting from the incorporation of a chemical enhancer in the vehicle. This paper investigates the behaviour of the system under iontophoretic conditions and also under those of combined physical and chemical enhancement. The data presented here are directly comparable to previous work by Nolan et al. [; Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2006. Combined effects of iontophoretic and chemical enhancement on drug delivery. II. Transport across human and hairless murine skin. Int. J. Pharm., submitted for publication] which investigated the behaviour of cationic compounds under analogous conditions. The iontophoretic release of diclofenac in the presence of model enhancers is thoroughly investigated. It is also shown that a range of anionic drug molecules undergo an electrochemical change during the course of the experiments which leads to their poor detection. This may be a factor in the under reporting of iontophoretic delivery of anionic drugs in the literature. However, it has been shown that the transport of the drugs is greatly enhanced by the application of an iontophoretic current. Results of combined enhancement studies provide a positive basis on which to proceed with in vitro studies of the system across human skin.

Release characteristics of anionic drug compounds from liquid crystalline gels

This is the second in a series of papers that report on the release and transport of a range of anionic drugs (diclofenac, salicylic acid) from liquid crystalline gels and ultimately on their use in transdermal delivery. The previous paper [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels for transdermal delivery. Part I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236] investigated passive release profiles across a non-rate-limiting membrane: here we report on the search for a suitable model enhancer (benzyl dimethyldodecyl ammonium bromide) for the transdermal delivery of anionic compounds. The results presented reveal a significant role for ion pairing and for buffering, analogous to those found in the investigations of cationic species (salbutamol) by Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2003. Iontophoretic and chemical enhancement of drug delivery. Part I. Across artificial membranes. Int. J. Pharm. 12, 41-55. The method of vehicle preparation is also investigated. It is shown that ion pairing of the drug with the enhancer decreases the amount of drug available for transport from the liquid crystalline gels into aqueous receptor media. This decrease is directly related to the ratio of the concentration of drug to that of the enhancer. Buffering the vehicle inhibits the ion-pair formation to some extent. Vehicle preparation was also found to influence the degree of ion-pair association. The inclusion of a similarly charged enhancer (oleic acid) to the drug was found not to impede the diffusion of the drug from the gels.