PPT On DRUG TRANSPORT MECHANISMS

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DRUG TRANSPORT MECHANISMS Presentation Transcript:
1.DRUG TRANSPORT MECHANISMS

2.MECHANISM OF TRANSPORT ACROSS THE MEMBRANE

3.MECHANISMS OF DRUG TRANSPORT

4.PASSIVE DIFFUSION
Passive diffusion is the process by which molecules spontaneously diffuse from a region of higher concentration to a region of lower concentration.
e.g. Propranolol, Ketoprofin

5.CHARACTERISTICS OF PASSIVE DIFFUSION
Transcellular process
Requires no energy and carrier
Not saturable
Depends on lipid solubility
Small mol.wt and lipophilliic molecules are primarily transported by this mechanism.

6.Hydrophilic drug (ionized or polar) is readily absorbed via aqueous channels or pores in cell membrane.
Lipophilic  soluble drug (nonionized or non polar) is readily absorbed via cell membrane itself.

7.Passive diffusion across GI-blood barrier can be described by Fick’s First law of diffusion:
dC/dt = Rate of drug diffusion
D = Diffusion Coefficient of the drug
A= Surface area of the membrane
k =Partition coefficient of the drug
Cgi =Concentration of drug in GI lumen
Cb= Concentration of drug in blood
h= Thickness of GI membrane

8.The passively absorbed drug enters the blood, gets diluted and distributed into a larger volume of body fluids.
Hence, the concentration of drug at absorption site Cgi is maintained greater than the concentration in the plasma (Cgi>>Cb). Such a condition is called sink condition for drug absorption.

9.If D, A and h are kept constant and Cgi>>Cb  (sink condition), the equation of fick’s law can be reduced as follows

10.Most of the drugs are weak electrolyte and exist in aqueous solution as ionized and unionized species.
The ionization of the drug is determined by pKa of the drug and pH of the environment, according  to Henderson Hasselbalch equations for weak acids and bases.
The nonionized species is more lipid soluble than the ionized species, and it partitions more readily across cell membranes.

11.CARRIER  MEDIATED TRANSPORT
Involves a carrier which reversibly binds to the solute molecules and forms a solute-carrier complex.
This molecule transverse across the membrane to the other side and dissociates, yielding the solute molecule.
The carrier then returns to the original site to accept a new molecule. 

12.MECHANISM  Carrier molecules within the cell membrane are involved in carrier-mediated transport mechanisms. The molecule to be transported binds to the carrier molecule, the three-dimensional shape of the carrier molecule changes, and the transported molecule is moved to the opposite side of the cell membrane. the transported molecule is then released by the carrier molecule, which resumes its original shape and is available to transport another molecule. EXAMPLE: large, water-soluble molecules or electrically charged ions across the cell membrane.

13.CARRIER MOLECULES   EXHIBIT:
Specificity for single molecules (substrate)
Competition among substrates for transport carrier
Saturation when all carriers are occupied
This is called Tm (transport maximum)

14. TYPES OF CARRIER MEDIATED TRANSPORT
There are two types of
carrier mediated transport
system
Facilitated diffusion
Active transport

15.. FACILITATED DIFFUSION
     Facilitated diffusion is a carrier-mediated transport process that moves substances into or out of cells from a higher to a lower concentration of that substance. Because movement is with the concentration gradient, metabolic energy in the form of ATP is not required.