a The absorption process is driven by the concentration gradient existing across the membrane, with the passage of drug molecules occurring primarily from the side of high drug concentration
◼ The absorption process is driven by the concentration gradient existing across the membrane, with the passage of drug molecules occurring primarily from the side of high drug concentration
a Ficks first law the rate of diffusion or transport across a membrane (dc/dt is proportional to the difference in drug concentration on both sides of the membrane dc/dt=P(CrC2) in which Ci and C2 refer to the drug concentrations on each side of the membrane and p is a permeability coefficient or constant
◼ Fick’ s first law: the rate of diffusion or transport across a membrane (dc/dt) is proportional to the difference in drug concentration on both sides of the membrane. -dc/dt=P(C1 -C2 ) in which C1 and C2 refer to the drug concentrations on each side of the membrane and P is a permeability coefficient or constant
Absorption site Blood Biologic membrane For practical purposes the value of C1-C2 may be taken simply as that of C and the equation written in the standard form for a first order rate equation: dc/dt=PC1
For practical purposes the value of C1 -C2 may be taken simply as that of C1 and the equation written in the standard form for a first order rate equation: -dc/dt=PC1 Absorption site C1 Blood C2 Biologic membrane
The gastrointestinal absorption of most drugs from solution occurs in this manner in accordance with first order kinetics in which the rate is dependent on drug concentration The magnitude of the permeability constant, depends on a the diffusion coefficient of the drug a the thickness and area of the absorbing membrane a the permeability of the membrane to the particular drug
The gastrointestinal absorption of most drugs from solution occurs in this manner in accordance with first order kinetics in which the rate is dependent on drug concentration. The magnitude of the permeability constant, depends on ◼ the diffusion coefficient of the drug ◼ the thickness and area of the absorbing membrane ◼ the permeability of the membrane to the particular drug
Because of the lipoid nature of the cell membrane, it is highly permeable to lipid soluble substances a Because biologic cells are also permeated by water and lipid-insoluble substances, it is thought that the membrane also contains water-filled pores or channels that permit the passage of these types of substances
◼ Because of the lipoid nature of the cell membrane, it is highly permeable to lipid soluble substances. ◼ Because biologic cells are also permeated by water and lipid-insoluble substances, it is thought that the membrane also contains water-filled pores or channels that permit the passage of these types of substances