Ocular tolerability and in vivo bioavailability of poly(ethylene glycol) (PEG)-coated polyethyl-2-cyanoacrylate nanosphere-encapsulated acyclovir

Pharmaceutical applications of mucoadhesion for the non-oral routes

The adhesion of pharmaceutical formulations to the mucosal tissue offers the possibility of creating an intimate and prolonged contact at the site of administration. This prolonged residence time can result in enhanced absorption and, in combination with a controlled release of the drug, also improved patient compliance by reducing the frequency of administration. During the almost 30 years over which mucoadhesion has been studied, a considerable amount of knowledge has been gained, and much has been learned about the different mechanisms occurring at the formulation-mucus interface and the properties that affect these mechanisms. The in-vivo performance of a dosage form not only depends on the mechanisms occurring at the interface, but also on the properties of the total mucoadhesive complex: the dosage form, the mucosa and the interface between them. A wide variety of methods are used for studying mucoadhesion; some rather similar to the in-vivo situation and some mimicking the interface alone. In this review, the mucus surface, the methods used for the study of mucoadhesion, the different mechanisms involved in mucoadhesion and theories underpinning them have been described. The complexity of mucoadhesion when trying to systemize the subject will also be discussed. The last part of the review describes the buccal, nasal, ocular, vaginal and rectal routes and provides examples of what can be achieved in-vivo when using mucoadhesive formulations.

Poly(alkylcyanoacrylates) as biodegradable materials for biomedical applications

This review considers the use of poly(alkylcyanoacrylates) (PACAs) as biomedical materials. We first present the different aspects of the polymerization of alkylcyanoacrylate monomers and briefly discuss their applications as skin adhesives, surgical glues and embolitic materials. An extensive review of the developments and applications of PACAs as nanoparticles for the delivery of drugs is then given. The methods of preparation of the nanoparticles are presented and considerations concerning the degradation, in vivo distribution, toxicity and cytotoxicity of the nanoparticles are discussed. The different therapeutic applications are presented according to the route of administration of the nanoparticles and include the most recent developments in the field.

Influence of preparation conditions on acyclovir-loaded poly-d,l-lactic acid nanospheres and effect of PEG coating on ocular drug bioavailability

PURPOSE

The evaluation of nanosphere colloidal suspensions containing acyclovir as potential ophthalmic drug delivery systems was carried out. The influence of polymer molecular weight and type and concentration of various surfactants on nanosphere properties was studied. The ocular pharmacokinetics of acyclovir-loaded nanoparticles was evaluated in vivo and compared with an aqueous suspension of the free drug.

METHODS

Nanospheres were made up of poly-d,l-lactic acid (PLA). The colloidal suspension was obtained by a nanoprecipitation process. The surface properties of PLA nanospheres were changed by the incorporation of pegylated 1,2-distearoyl-3-phosphatidylethanolamine. The mean size and zeta potential of the nanospheres were determined by light scattering analysis. The acyclovir loading capacity and release were also determined. In vivo experiments were carried out on male New Zealand rabbits. The ocular tolerability of PLA nanospheres was evaluated by a modified Draize test. The aqueous humor acyclovir levels were monitored for 6 h to determine the drug's ocular bioavailability for the various formulations.

RESULTS

A reduction of the mean size and a decrease of the absolute zeta potential of PLA nanospheres resulted from increasing the surfactant concentration. The higher the polymer molecular weight, the smaller the nanosphere mean size. PEG-coated and uncoated PLA nanospheres showed a sustained acyclovir release and were highly tolerated by the eye. Both types of PLA nanospheres were able to increase the aqueous levels of acyclovir and to improve the pharmacokinetics profile, but the efficacy of the PEG-coated nanospheres was significantly higher than that of the simple PLA ones.

CONCLUSIONS

PEG-coated PLA nanospheres can be proposed as a potential ophthalmic delivery system for the treatment of ocular viral infections.

Corneal permeation of ganciclovir: mechanism of ganciclovir permeation enhancement by acyl ester prodrug design

Ganciclovir (GCV), a promising antiviral compound, has poor ocular bioavailability as a result of its relatively low partition coefficient. In this study, lipophilic ester prodrugs of GCV were synthesized in an effort to improve its uptake into ocular tissues. In vitro permeability studies were conducted on isolated rabbit corneal membranes using aliphatic mono-acyl ester prodrugs of GCV to determine the effect of lipophilicity and corneal hydrolysis rate on transcorneal diffusion. The GCV prodrugs showed a progressive decrease in solubility and a corresponding increase in Log P values as the chain length was ascended. Permeation studies using freshly isolated rabbit corneas showed that all prodrugs permeated as intact prodrug as well as hydrolyzed GCV. Corneal permeability coefficients increased with increasing lipophilicity for mono-ester prodrugs having more than three carbon atoms in the side chain. The permeability of GCV increased about 6-fold in ascending from the parent drug-ganciclovir (3.82 +/- 0.19 x 10(-6) cm sec(-1)) to its valerate ester prodrug (23.70 +/- 1.36 x 10(-6) cm sec(-1)). Among the prodrugs studied, the valerate ester showed the highest permeability and holds the most potential for development. Overall prodrug permeability correlated linearly with increased susceptibility of the GCV esters to undergo hydrolysis in the cornea. The present work indicates that the ideal prodrug is one that not only possesses enhanced partitioning characteristics, but also high enzyme susceptibility. Concentration of active GCV penetrating the corneal epithelium was substantially increased through the bio-reversible ester prodrug strategy.