The aim of present work is to study the in-vitro drug-drug interaction studies of levocetirizine with HMG-CoA reductase inhibitors (atorvastatin, simvastatin and rosuvastatin) in different pH environments in simulated gastric juice (pH 1) simulating full stomach juice (pH 4), blood pH (pH 7.4) and simulated GI (pH 9) at physiological temperature (37°C). The interactions were carried out using dissolution apparatus and dug contents were analyzed by UV-Visible spectrophotometer. The availability of levocetirizine in the presences of HMG-CoA reductase inhibitors were determined by deriving a simultaneous equation for two component system through modification of Beer's law. It was observed that availability of levocetirizine after interaction with MG-CoA reductase inhibitors was increased or decreased due to the formation of charge transfer complexes between them.