Drug absorption and factors affecting absorption

3. GENERAL
PHARMACOLOGY

5. DEFINITION:
It’s a branch of science which deals with the interaction between the
externally administered chemical molecules with living tissues or
systems.
OR
The science that deals with the origin, nature, chemistry, effects, and
uses of drugs.

6. GENERAL PHARMACOLOGY
Pharmacokinetics
• What the body does to the drug
• Absorption
• Distribution
• Metabolism
• Excretion
Pharmacodynamics
• What drug does to the body

8. Drugs in dosage
form
Drug in solution
Site of action
bound
free
Free drug
Protein bound Metabolites
Storage tissue
free
bound
Biotransformation
Absorption Distribution - Storage Excretion
Urine
Bile
Faeces
Sweat
Saliva

10. The Absorption of the drug depends upon
these mechanism
1. Passive Transport
2. Pore Transport
3. Carrier Mediated Transport
• Facilitated Diffusion
• Active Transport
4. Ionic or Electro Chemical Diffusion
5. Ion Pair Transport
6. Endocytosis
• Pinocytosis
• Phagocytosis

16. IONIC / ELECTRO CHEMICAL
DIFFUSION
Charge on the membrane influence the diffusion of the drug. The unionised drug
can easily pass through the membrane than ionised drug but most of our drugs are
available as weak electrolytes.
Unionised drugs > Ionised drugs > cation drugs
(more) (moderate) (less)
If the drug and the membrane are having opposite charge then the absorption
takes place faster. If the drug and membrane having same charge then the external
energy is required for absorption.

22. ABSORPTION
• Drug Related Factor :
1. Physical properties of drugs
2. Nature of the drug
• Patient related factors
1. Physiological factors
2. Dosage forms

23. DRUG RELEATED FACTOR
1. Physical state :
• The state of drug i.e. solid or liquid : liquid state is more rapidly absorbed then solid state.
• Solubility : aqueous soluble drugs easily gets absorbed then insoluble or leastly soluble drugs.
2. Nature of dosage form :
• Particle size : Particle size ∝ I
Absorption
• Disintegration time and dissolution : lesser time for disintegration will leads faster dissolution
which directly increases the absorption.
• Tablets
• Capsules Rate of
• Powder disintegration
• Emulsion
• Suspension
• Solution { syrups}

24. PATIENT RELEATED FACTORS
1. Physiological factors :
• Ionisation : Majorly the drugs are available in the ionised form. If the charge of the drug and
the membrane is in opposite direction will helps in faster moment of the drugs across the
membrane. Unionised drugs have faster rate of absorption.
2. GI Transits Time :
• Presence of food volume viscosity will influence the absorption of drug like the tetracycline
should not be taken along with the milk will leads to formation of complex and finally results in
decreasing the absorption.
3. Tonicity :
• The tonicity should be maintained optimum for maintenance of osmotic of osmotic pressure
which helps in pushing the drug from the cell blood and vice versa.
4. Area Of Absorption :
• Area ∝ Absorption
Intestine is having more area then stomach hence maximum absorption of drug takes place in
intestine.