1. Pharmacokinetics
Dr. Farhan Ahmad

3. • the magnitude of response depends on
concentration of the drug at the site of
action

4. PHARMACOKINETICS
What the body does to drug
• ABSORPTION
• DISTRIBUTION
• METABOLISM
• EXCRETION

5. Absorption
The movement of a drug from its
point of entry into the body into
systemic circulation

6. • I.V- completely (100%) absorbed
• Oral- delayed and incomplete.

7. • Rate: how rapidly does the drug get from
its site of administration, to the general
circulation?
• Extent: How much of the administered
dose enters the general circulation (per cent
bioavailability = F)?

10. Absorption of Drugs
1. Sites of absorption through the GI tract
2. Factors that modify absorption in the GI tract
3. Bioavailability
4. Other sites of drug administration/absorption
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11. Absorption of Drugs
1. Sites of absorption through the GI tract
1) Mouth
2) Stomach
3) Small intestine
4) Large intestine
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12. Absorption of Drugs
2. Factors that modify absorption in the GI tract
1) Drug solubilization
2) Ph of the medium
3) Lipid solubility of the drug
4) Blood flow at the absorption site
5) Surface area of absorption
6) Route of administration (First Pass Effect in Oral Route)
7) Gastric emptying
8) Food
9) Intestinal motility
10) Metabolism of drug by GI tract
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13. Absorption of Drugs
Factors that modify absorption in the GI tract
 Drug solubilization – breaking drugs into smaller, more
absorbable particles
.
DISINTEGRATION (solid )
⇓
DISSOLUTION (solution)
⇓
ABSORPTION
⇓
SYSTEMIC CIRCULATION (% bioavailability)
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14. Ph of the medium
stomach (pH 1~3)
in favour of weak acid
absorption
duodenum (pH 5~7)
in favour of weak base
absorption
ileum (pH 7~8)
in favour of weak base
absorption

15. pH and ionization
Acidic drugs are best absorbed in Acidic
medium
Basic drugs are best absorbed in Basic
medium

16.  Gastric emptying
small intestine – primary site of drug absorption
Anything that delays/accelerates gastric emptying will
decrease/increase drug absorption.
 Food
High fat food – delay gastric emptying – slow
absorption
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18. Bioavailability
Bioavailability is defined as the fraction of unchanged drug
reaching the systemic circulation following administration
by any route .
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19. Bioavailability of a drug
• The bioavailability of a drug (by a route
other than intravenous) is given by:
AUC (extra vascular)
• F= -----------------------------
AUC (intravenous)