o 2. transportation of drugs across membranes o The absorption, distribution, biotransformation and excretion of a drug all involve its passage across cell membranes Transported model: ●(1) Passive diffusion o It transports along a concentration gradient ●※ It needs not metabolic energy ●※ it is usually determined by its pka, lipid- water partition coefficient, molecular weigh, and ph gradient in solution⚫ 2. transportation of drugs across membranes ⚫ The absorption, distribution, biotransformation, and excretion of a drug all involve its passage across cell membranes. ⚫ Transported model: ⚫ ⑴Passive diffusion ⚫ It transports along a concentration gradient ⚫ ※ It needs not metabolic energy ⚫ ※ it is usually determined by its pKa, lipid￾water partition coefficient, molecular weigh, and pH gradient in solution