Introduction:
Acyclovir, an antiviral drug is used for treatment of herpes simplex virus infections. It has an oral bioavailability of only 10 to 30 % (limiting absorption in GIT to duodenum and jejunum); half life about 3 hrs, soluble only at acidic pH (pKa 2.27). The poor bioavailability of acyclovir is attributed to short retention of its dosage form or inadequate availability of unionized drug at the absorption sites (absorption window), due to non-site specific conventional drug delivery systems.

Objectives:
i) To investigate formulation variables (such as stabilizer concentration, drug to polymer ratio etc.) to optimize the processing of nanoparticles.
ii) Invivo evaluation of developed site specific nanospheres for delivery of acyclovir.

Method:
Nanospheres were prepared using precipitation method and evaluated in vitro,and ex-vivo. Poly (methacrylic acid ethyl acrylate)1:1 i.e.Eudragit L100-55 was used as polymers and Pluronic F68 used as stabilizer. The prepared formulations were further evaluated.

Result:
Particle size of the nanoparticles prepared by nanoprecipitation method has been found to be in the range of 550nm to 1200nm. Drug to polymer ratio and concentration of surfactant were found to influence the particle size and entrapment efficiency of acyclovir loaded nanoparticles. Invitro drug release study showed significant increase in the release of the drug in the pH environment prevalent in duodenum and jejunum. This is due to pH dependent solubility of Eudragit L l00-55 i.e. nanocoating of polymer, is resistant to gastric juice but the coat dissolves readily above pH 5.5. Thus developed nanoparticles have a good potential to have enhanced bioavailability due to site specific delivery.

Conclusion:
From study it could be concluded that acyclovir loaded Eudragit nanospheres, prepared by precipitation method, can release the drug at site in the GIT where drug absorption is maximum. Thus indicating a promise of enhanced bioavailability as compared to conventional dosage forms.