PHARMACOKINETICS-DRUG ABSORPTION

3. Pharmacokinetics(PK) is the quantitative study
of drug movement in, through and out of the
body.

5. PHASES OF PHARMACOKINETICS
1. ABSORPTION
2. DISTRIBUTION
3. METABOLISM/BIOTRANSFORMATION
4. EXCRETION

8. MECHANISM OF DRUG TRANSPORT

9. Mechanism of Drug
Absorption
Drugs are transported across
membrane by:
1. Passive diffusion and
filtration
2. Specialized transport
a) Active transport:
Primary& secondary
b) Facilitated diffusion
3. Endocytosis: Pinocytosis
Phagocytosis
MECHANISM OF DRUG TRANSPORT

10. Mechanism of Drug AbsorptionMECHANISM OF DRUG TRANSPORT

11. MECHANISM OF DRUG TRANSPORT

12. MECHANISM OF DRUG TRANSPORT

14. • Passage of a drug from site of administration to
the bloodstream.
• It is important for all routes of administration
except i.v. injection, where the need for
absorption is bypassed entirely.
• Week acidic drugs in acidic environment
= H+ + A- <-> HA(unionized)
• Week basic drugs in acidic environment
= H+ + NH3 <-> NH4
+ (ionized)

16. • It is a measure of fraction of unchanged drug
reaching systemic circulation following
administration by any route.
• I.V. route – 100%
• Other routes – Incomplete
• e.g. Bioavailability of Paracetamol is 50%. It
means if a patient orally takes 500mg
paracetamol, only 250mg(50%) of drug will
reach to the systemic circulation.

17. Factors affecting Drug
Absorption/Bioavailability
 Drug related
1. Physical properties
• Physical state
• Lipid /water solubility
2. Nature of the dosage form
• Particle size
• Disintegration and Dissolution time
• Formulation
 Patient related
1. Physiological factors
• Degree of ionization
• pH of the GI fluid
• GI transit time
• Area of absorbing surface
• Presence of other agents
•
• Enterohepatic cycling
2. Disease states – malabsorption

19. FIRST PASS METABOLISM
“Inactivation of the drug before reaching the
bloodstream”
or
“Metabolism of a drug during its passage
from the site of absorption to the systemic
circulation”

20. FIRST PASS METABOLISM
• Also called as presystemic metabolism or first pass effect.
• It is an important feature of oral route.
Where does it occur?
• Liver
• Gut wall
Results in;
 Low bioavailability (Low conc. of drug in blood).
 Short duration of action.
 Drugs with high first pass effect should not be given orally but
parenterally.

22. FIRST PASS METABOLISM
Clinical significance:
• Dose has to be increased. eg; Propronolol
• Route has to be changed. eg; Insulin
Hydrocortisone
• Marked individual variation in the oral dose due to
differences in first pass effect.
• Oral bioavailability is markedly increased in patients with
liver disease.

23. FIRST PASS METABOLISM OF SOME
IMPORTANT DRUGS