This document discusses drug absorption, which is the transfer of a drug from its site of administration into the bloodstream. There are three main processes of drug absorption: passive diffusion, carrier-mediated transport, and endocytosis/exocytosis. Passive diffusion is the movement of uncharged drug molecules through membranes down a concentration gradient via simple or facilitated diffusion. Carrier-mediated transport uses protein carriers in membranes to move drugs either with or against a concentration gradient. Endocytosis involves a drug molecule being engulfed by a cell membrane, while exocytosis is the reverse process of substance secretion from a cell.

1. ““__IN THE NAME OF ALLAHIN THE NAME OF ALLAH
THE MOST BENEFICIENTTHE MOST BENEFICIENT
AND THE MOSTAND THE MOST
MERCIFULL_”MERCIFULL_”

2. ABSORPTION OF DRUGSABSORPTION OF DRUGS
Definition:-Definition:-
““__It is the__It is the
transfer of drug from itstransfer of drug from its
site of administration intosite of administration into
the blood stream__”the blood stream__”

3. PROCESS OF DRUGPROCESS OF DRUG
ABSORPTIONABSORPTION
Depending on the chemicalDepending on the chemical
properties,drugs may b absorbed by eitherproperties,drugs may b absorbed by either
 ExocytosisExocytosis
 Carrier mediated transpotCarrier mediated transpot
 Endocytosis and exocytosisEndocytosis and exocytosis

4. PASSIVE DIFFUSION:-PASSIVE DIFFUSION:-
““__Passage of drugs molecules by diffusing as un-__Passage of drugs molecules by diffusing as un-
ionized moiety through lipid membrane__”ionized moiety through lipid membrane__”
DEPENDS ON:-DEPENDS ON:-
i.i. molecular sizemolecular size
ii. molecular chargeii. molecular charge
iii. lipid-water partition co-efficientiii. lipid-water partition co-efficient
iv. conc. gradientiv. conc. gradient

5. 1.SIMPLE DIFFUSION:-
“__Driving force for absorption is the
concentration gradient across a
membrane seperating two body
compartments__”

6. Characteristics:-
 Doesn’t involve carrier
 Process is not saturated
 Shows low stuctural specificity

7. Importance:-
Vast majority of drugs gain access to the
body by this mechanism.

8. I.FICK’S LAW OF DIFFUSION:-
“_Passive flux(F)of unionized molecule across the
lipid membrane is_” :
 Directly propotional to conc.gradient(C1-C2).
 Area(A) across which diffusion occurs.
 Permeability(P) co-efficient.
 Inversely propotional to thickness(T) of diffusion path.

9. II.Diffusion of weak acids &basesII.Diffusion of weak acids &bases
Many drugs are either weak acidsMany drugs are either weak acids
or weak bases.or weak bases.
i.Acidic drugs dissociates as;i.Acidic drugs dissociates as;
HA________H*+AHA________H*+A
ii.Basic drugs dissociates as;ii.Basic drugs dissociates as;
BH*_______B(unprotonated)BH*_______B(unprotonated)
+H*+H*

10. Diffusion stateDiffusion state
 For weak acids-----Prontonated formFor weak acids-----Prontonated form
 For weak base-----Unprotonated formFor weak base-----Unprotonated form

11. Determination of the ratio of charged and
uncharged form
pH at the site of absorption
Strength of weak acid & weak bases(pKa)
Decrease pKa ----- stronger the acids
Increase pKa ----- stronger the bases

12. Determination of presence of amount of drugDetermination of presence of amount of drug
on either side of membrane:-on either side of membrane:-
It is represented byIt is represented by HANDERSON-HASSELBALCHHANDERSON-HASSELBALCH equation..equation..
pH=pKA+logpH=pKA+log unprotonated speciesunprotonated species
protonated speciesprotonated species
i.For acidsi.For acids
pH=pKa+logpH=pKa+log (A)(A)
(HA)(HA)
ii.For basesii.For bases
pH=pKa+logpH=pKa+log (B)(B)
(BH)(BH)

13. B.Carrier mediated diffusion:-B.Carrier mediated diffusion:-
““__Movement of drug across the__Movement of drug across the
membrane mediated by carriermembrane mediated by carrier
protein in the membrane__”protein in the membrane__”

14. Characteristics:-
 Saturable process
 Specific for chemical stucture of the drug.

15. TYPESTYPES
1.Facilitated diffusion:-1.Facilitated diffusion:-
““_Movement is driven by_Movement is driven by
concentration gradient for which no energy isconcentration gradient for which no energy is
required_”required_”
2.Active transport:-2.Active transport:-
““_Movement occur against a_Movement occur against a
conc. gradient that requires ATP which isconc. gradient that requires ATP which is
generated by Na-K ATPase.generated by Na-K ATPase.

16. C.Endocytosis:-C.Endocytosis:-
““ _Process by which_Process by which
drug molecule is engulfed by celldrug molecule is engulfed by cell
membrane_”membrane_”
Exocytosis:-Exocytosis:-
““ _Reverse processis_Reverse processis
responsible for secretion of manyresponsible for secretion of many
susbatance from the cell_”susbatance from the cell_”