圈生一Process of drug absorption 国生 Physicochemical factors-Dissolution ©Diffusion model ®Introduction Nernst-Brunner equation .Getting the drug into its site of absorption dQ .Getting the drug into solution:factors affecting the rate of dissolution =DAC:-Cp) dt h .Gastrointestinal membrane transport D-diffusion coefficient of the drug .Moving the drug away from the site of absorption A=effective surface area of the drug particles The slowest of the four steps will determine the rate of h=thickness of a stationary layer of solvent availability of the drug from an oral dosage form. Cs=saturation solubility of the drug C=concentration of drug in the bulk fluids 国线一 国生Physicochemical factors-Dissolution ©Diffusion model Factors influencing drug absorption and drug Nernst-Brunner equation Q-DAC,-C) availability .Noyes-Whitney equation .Physicochemical factors 市=&G-) Physiological factors .S:surface area of drug exposed to the dissolution media ·Other factors .D:diffusion coefficient .V:volume of the dissolution media .h:thickness of a stationary layer of solvent 国线一 国生 Physicochemical factors-Dissolution Nernst-Brunner equation Physicochemical factors 4Q-DAC.-C) ·Dissolution溶出 ·Oil/water partition coefficient(油水分配系数) Effective surface area of the drug ·pKa .Saturation solubility of the drug ·Molecular weight Drug concentration in bulk solution ·Diffusion coefficient .Thickness of the stationary diffusion layer 44 Shanghai Jiao Tong University Process of drug absorption Introduction • Getting the drug into its site of absorption • Getting the drug into solution: factors affecting the rate of dissolution • Gastrointestinal membrane transport • Moving the drug away from the site of absorption The slowest of the four steps will determine the rate of availability of the drug from an oral dosage form. Shanghai Jiao Tong University Factors influencing drug absorption and drug availability • Physicochemical factors • Physiological factors • Other factors Shanghai Jiao Tong University Physicochemical factors • Dissolution 溶出 • Oil/water partition coefficient(油水分配系数) • pKa • Molecular weight Shanghai Jiao Tong University Physicochemical factors-Dissolution Diffusion model • Nernst-Brunner equation D=diffusion coefficient of the drug A=effective surface area of the drug particles h=thickness of a stationary layer of solvent CS=saturation solubility of the drug Cb =concentration of drug in the bulk fluids Shanghai Jiao Tong University Physicochemical factors-Dissolution Diffusion model • Nernst-Brunner equation • Noyes-Whitney equation • S: surface area of drug exposed to the dissolution media • D: diffusion coefficient • V: volume of the dissolution media • h: thickness of a stationary layer of solvent KS(C C ) dt dC  S  Vh D K  Shanghai Jiao Tong University Nernst-Brunner equation • Effective surface area of the drug • Saturation solubility of the drug • Drug concentration in bulk solution • Diffusion coefficient • Thickness of the stationary diffusion layer Physicochemical factors-Dissolution