In Vitro Drug Release Profile
In vitro drug release profile was conducted on the optimised formulation by employing a dialysis bag method with USP apparatus II. Two sets of dialysis bag (MWCO: 14,000 Da) of suitable length to accommodate the sample were prepared and immersed in 37°C ultrapure water for 30 min for stabilisation. One end of the dialysis bags was tied securely with thread. Then 4 mL of optimised formulation with ACV concentration of 1 mg/mL was injected into each dialysis bag. Another end of the dialysis bags was then tied securely with a thread. The dialysis bags were kept in sink condition in two separated vessels of a RC-8DS dissolution tester (Sinopham Co., Ltd., China) filled with 400 mL of pH 1.2 hydrochloric acid buffer (SGF) and 400 mL of pH 6.4 phosphate buffer saline (SIF) respectively. Dissolution tester was set for 70-rpm rotation and 37°C water bath. One millilitre of sample was taken in triplicate at 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h. The same volume of fresh medium was re-filled into the corresponding vessel. Samples were analysed with HPLC method as described in section E. Another calibration curve with a smaller range from (1) was generated to ensure the accuracy of ACV concentration derived from peak area. Equation (3) showed a calibration curve that fit over the range of 5 to 50 μg/mL with r2 of 0.99964.3 y=125.32389x+79.70511
The drug release profile of optimised formulation was plotted with a cumulative percentage of ACV released against time. Drug release data was fitted into one of the releasing models which were zero order, first order, Higuchi, Korsmeyer-Peppas, and Hixson-Crowell releasing model. A best model kinetic fit describing drug release of the formulation was selected according to the coefficient of determination (r2) that calculated with aid from Microsoft Excel. Equation (4) was used as a formula for the cumulative percentage of drug-released calculation.4 DR%=Mreleased/Mtotal100%where DR was the cumulative percentage of drug released, and Mreleased and Mtotal were mass of acyclovir released and total mass of acyclovir in formulations used respectively.