A basic introductory presentation explaining the Absorption of drugs in the body

1. ABSORPTION OF
DRUGS
Harsha Negi
B.Pharm
Amity Institute of Pharmacy

2. • Pharmacokinetics
• Absorption
• Distribution
• Metabolism(Biotransformation)
• Excretion

4. Routes of drug administration
• Enteral(Through Alimentary tract)
• Oral
• Sublingual or buccal
• Rectal
• Parenteral(Through Injection)
• Intravenous
• Intramuscular
• Subcutaneous

5. • Intradermal
• Intraperitoneal
• Intrapleural
• Intracardiac
• Intra-arterial
• Intrathecal
• Intra-articular

8. • Absorption is the transfer of a drug from its site of
administration to the blood stream.

9. Factors affecting drug absorption:
• Lipid-water partition co-efficient: Non
electrolyte drug depends upon lipid solubility.
• More lipid soluble and less water soluble that
is it has high lipid-water partition co-efficient,
it will absorbed rapidly

10. • 2- Drug solubility: drugs given in aqueous solutions
are more rapidly soluble than when given in oily
solution, suspension or solid form.
• 3- Dosage form: Tablets and capsules, rate of
disintegration and dissolution is limiting factor in
their absorption. After dissolution, smaller the
particle size, more efficient will be absorption

11. • 4- Circulation at the site: Increased blood flow
increase absorption
• 5- Area of absorbing surface : Absorbed more from
large surface areas for example intestinal mucosa

12. • 6- Effect of pH: Most drugs are either weak acids or
weak bases. Weak electrolytes, in addition to lipid
solubility, depends upon its degree of ionization
which is influenced by pH of the area.
• Weak acids become less ionized(charged) in an acidic
medium and weak bases become less ionized in an
alkaline medium
• Unionized drug is lipid soluble and diffusible

13. Lipid soluble(hydrophobic), uncharged, unionized
will cross the membrane rapidly than lipid
insoluble(hydrophilic or water soluble),charged and
ionized.
• Basic drug will absorb more from intestine because it
becomes unionized in basic medium. In acidic
medium basic drug will become more ionized and
thus no absorption will takes place.

14. • Functional integrity of the GIT: Increased peristaltic
activity as in diarrhea reduces drug absorption
• Increased gastric emptying time, absorption will be
more.

15. Bioavailability
• The fraction of unchanged drug reaching the systemic
circulation following administration by any route”
or
The percentage of administered drug that reaches the
systemic circulation in a chemically unchanged form”
• Thus by definition a drug that is administered by
intravenous route has 100% bioavailability

16. Mechanism of Drug Transport
• Passive diffusion
• Specialized transport : a) carrier mediator
b) pinocytosis

17. Passive Diffusion

18. Specialized Transport
Carrier mediated transport :

19. Facilitated Diffusion

21. Active Transport

23. Pinocytosis

24. Bioavailability
• Bioavailability refers to the rate and extent
of absorption of a drug from dosage form .
• It is a measure of the fraction of
administered dose of a drug that reaches
the systemic circulation in the unchanged
form.

25. • Main organ of metabolism
is liver
• Specific drugs are
metabolized in gut wall,
skin, lungs

26. Factors affecting bioavailability
• First-pass hepatic metabolism:
• when a drug is absorbed across GIT, it enters the
portal circulation before entering the systemic
circulation.
• If the drug is rapidly metabolized by the liver ,the
amount of unchanged drug that gains access to the
systemic circulation is decreased

27. • Absorption
• Solubility of the drug: hydrophobic drug will absorb
more so bioavailability will be more
• Chemical instability: some drugs are unstable in pH
of the gastric contents. Others are destroyed in GIT
by degradative enzymes e.g. insulin so
bioavailability?
• Particle size: smaller the particle size more
absorption will be there. so bioavailability?

28. Plasma half life
• The time required for the concentration of drug in the
plasma to decrease to one half of its initial value.
• for example if the initial conc. of drug is 100mg and
if the half life is 1 hr, only 50mg will remain in the
plasma at the end of 1 hr.

29. • Time : 0 1hr 2hr 3hr 4hr
• Cp (mg/dl): 100 50 25 12.5 6.25
• So from this table we can deduce that the half-life of
this drug is 1 hour.

30. Importance
• It denotes how quickly a drug is removed from the
plasma by biotransformation or excretion
• Since drug require a minimum conc. in the plasma to
produce pharmacological action, a drug which is
eliminated quickly requires more frequent dosing
than a drug with a long half life.
• It thus indicates the duration of action of drug and
therefore, it determines the frequency of
administration of dose of the drug for therapeutic
effectiveness.

31. References:
• Essentials of medical pharmacology by KD
Tripathi