Ganciclovir-loaded albumin nanoparticles: characterization and in vitro release properties

Ganciclovir is one of the most widely used antiviral drug for the treatment of cytomegalovirus retinitis. Due to its short half-life in the vitreous, frequent administrations are necessary to maintain the therapeutic levels. In this context, the aim of this study was to characterise and in vitro evaluate the drug release properties of three different formulations of ganciclovir-loaded albumin nanoparticles. These carriers were prepared by a coacervation method and chemical cross-linking with glutaraldehyde. Depending on the step where the drug and/or cross-linking agent were added three different formulations were obtained, named models A, B and C. For model A nanoparticles, ganciclovir was incubated with the just-formed albumin nanoparticles. For the other two types of nanoparticulate formulations, the drug was added to a solution of albumin (model B) and glutaraldehyde (model C) prior to the formation of the carriers by coacervation. In all cases, the size of the different nanoparticulate formulations was comprised between 200 and 400 nm and the yield ranged from 50%, in model A, to 65% in model B. Concerning the ganciclovir loading, model B nanoparticles offered the higher capacity to carry this antiviral drug (around 30 microg ganciclovir/mg nanoparticle). On the contrary, the drug loading calculated for model A nanoparticles was only 14.6 microg/mg. The in vitro release profiles of the nanoparticles showed a biphasic pattern, with an initial and rapid release, followed by a slower step for up 5 days. This burst effect was especially relevant in model A (around 60% in 1 h), followed by model B (40%) and less important in model C (20%). The addition of trypsin to the release medium did not have a significant influence on the release characteristics. However, the release of the drug was increased in acidic or basic mediums, due to the disruption of the covalent binding between ganciclovir and the protein matrix via glutaraldehyde. This strong linkage was also confirmed by TLC experiences. In summary, a first step of incubation between the drug and the protein, prior to the preparation of nanoparticles, enabled us to obtain albumin carriers able to release ganciclovir in a sustained way.