199SPECTROPHOTOMETRIC METHOD FOR ESTIMATION OF ACICLOVIR IN BULK AND TABLET DOSAGE FORMSimple, Sensitive, Precise, Accurate and Cost-effective Difference spectrophotometric method for the determination of Aciclovir in bulk and tablet dosage form has been described. The ultraviolet spectra of Aciclovir depends on the state of ionization of the functional group & consequently on the pH of the solution. The proposed method is based on the principle that, Aciclovir exhibits different spectral characteristics in alkaline medium (0.1 M Sodium hydroxide) & acid medium (0.1 M Hydrochloric acid), difference in absorptivity (∆A ) is directly related to concentration. Aciclovir in basic medium is scanned over UV region by taking acidic drug solution as blank. From the absorbance values, two wave lengths are selected one at 270 nm (positive peak) and another at 290 nm (negative peak). The sum of the absolute values at these wavelengths is called amplitude. The amplitude is proportional to the amount of drug. Factors affecting selection of optimum pH, choice of wave lengths for maximum accuracy and precession are discussed. Beer’s law is obeyed in the concentration range of 50-250 μg/ml with correlation coefficient of 0.999. The developed method has been successfully applied to pharmaceutical formulations without any interference from common excipients.vijaya82.hari@gmail.comResearch412013Aciclovir (ACV),Tablet dosage form, Spectral characteristicsAitha Vijaya LakshmiDepartment of Chemistry, Sri Krishnadevaraya University, Kurnool, Andhra Pradesh, India.