The drug entrapment efficiency of the nanoparticle formulations was calculated by indirect method which involded sedimentation of nanoparticles by ultracentrifugation followed by analysis of unentrapped drug in the supernetant. The difference between the amount of drug added initially in the formulation and unentrapped drug found in the supernetant gives the amount of drug entrapped in formulation. Briefly, nanoparticle suspensions were centrifuged at 15000 × rcf for 30 min. The supernetant obtained was analyzed by bouble beam UV spectrophotometer (UV 630, Jasco, Japan) at 224 nm after appropriate dilution. The % entrapment efficiency of the formulation was calculated as mentioned in Eq. (5) .
The drug loading capacity were calculated by direct method which involved comparison of practically loaded drug found in analysis of nanoparticle solution with that of theoretical amount of drug taken in beginning to load in the polymer (Eq.(6) ). Briefly, about 10 mg of dried nanoparticles were dissolved in acetone which was then diluted appropriately and analyzed by double beam UV spectrophotometer (UV 630, Jasco, Japan) at 224 nm.
The drug loading capacity were calculated by direct method which involved comparison of practically loaded drug found in analysis of nanoparticle solution with that of theoretical amount of drug taken in beginning to load in the polymer (Eq.