3. INTRODUCTION
•
Dosage form Dissolution Absorption
A Drug is rarely administer into its original form. Almost
Always, a convenient dosage form to be administer by a
Suitable route is prepared.
The components of dosage form and production methodologies
Can also influence the bioavailability of a drug
The difference in rate of absorption of drugs has been
modulated By selecting best formulation with suitable excepients.
5. Non-drug components which are added
during formulation of drug are called
excipients.
Excipients are added during drug formulation
because:
Ensures physico-chemical stability.
Gives uniformity to composition.
Gives optimum bioavailability.
Gives suitable colouration and taste.
6. Vehicle is the major component of liquid oral and parenteral
dosage form.
Basically, 3 types of vehicles are used
▪ Aqueous vehicles (water, syrup, etc)
▪ Non-aqueous water-miscible vehicles (propylene,
glycol, glycerol, etc)
▪ Non-aqueous water-immiscible vehicles (vegetable oils)
Aqueous and water miscible vehicles are miscible with
the body fluids so the drugs from them are rapidly absorbed.
Absorption of drugs in different vehicles follows the order :
water-miscible vehicles > aqueous vehicles >water-immiscible vehicles
7. Organic diluents:
Starch, lactose, microcrystalline cellulose, etc
Inorganic diluents:
Dicalcium phosphate (DCP) is most common.
Sometimes Drug-diluent interactions alters the
absorption of drug.
Example:
Tetracycline and DCP when interacts, divalent
calcium-tetracycline complex is formed which is
poorly soluble and thus unabsorbable.
InorganicOrganic
8. Large amount of such granulating agents
increases hardness and decreases dissolution
rates of tablets and hence decreases the rate
of absorption.
Example:
PEG 6000 when binds with phenobarbital, it forms complex
compound with very low solubility.
Starch, cellulose derivatives, gelatin, sugar
solutions,etc are most common granulating
agents.
Granulating agents are the substance which
are used to hold powders together to form
granules.
9. However, adsorbing disintegrants like bentonite and
vegum should be avoided with low dose drugs like
digoxin, alkaloids and steroids since a large amount of
dose is adsorbed and only a small fraction is available
for absorption.
Disintegrants are the substance which increases the
dissolution of tablets in water.
10. Lubricants are added to tablets to reduce
interparticle friction and sticking.
Also called as anti-frictional agents.
Lubricants are mostly hydrophobic in nature
and thus inhibits the penetration of water
into the tablets.
Lubricants are applied by coating it over the
surface of tablets.
11. Surfactants are used in drug formulations as
wetting agents, solubilizers,etc
Surfactants may either increase or retard the drug absorption
interacting with drug molecules.
Surfactants usually increases drug absorption by increasing
membrane permeability of the drug.
Decrease in absorption of drug in the presence of surfactant
is due to formation of unabsorbable drug-surfactant complex at
surfactant concentrations above the critical concentration.
Thus, higher surfactants concentration
always decreases the rate of drug absorption.
12. In some drugs, complexing agents are added
to alter the physico-chemical and biopharmaceutical
properties of a drug.
A complexed drug may have different
stability, solubility, molecular size, diffusion
rate, etc
Examples of complexation which increases
the drug absorption are:
Ergotamine tartarate – caffeine complex. (increases
dissolution)
Caffiene-PABA complex. (increases membrane
permeability)
13. The rate of absorption and bio-availability of certain drug
largely depends on the proper selection of dosage form of that
drug.
This is due to the relative rate at which a particular dosage
form releases the drug to the biological fluids and membrane.
As a general rule, bio-availability of a drug from various
dosage forms decreases in the following order:
Solutions > emulsions > suspensions >
powders > capsules > coated tablets >
enteric-coated tablets > sustained-release tablets.
14. High temperature and humidity results in
increase in hardness of tablets which
decreases the rate of absorption.
Therefore, storage conditions and product
age has significant role in the absorption of
drug from different dosage forms.
15. • Absorption plays an major role to attain the desired
therapeutic action with minimal side effects at the given
period of time
• Formulation factors influencing drug absorption helps us to
focus on formulating drug with proper attainment of
permeability of drugs to systemic circulation at given time
16. 1. Brahmankar D.M., Jaiswal S.B., First edition,
“Absorption of Drugs”Biopharmaceutics and
Pharmacokinetics – A treatise, Vallabh Prakashan, Delhi
1995,
page no. 27-77
2. Shargel L., Andrew B.C., Fourth edition “Physiologic
factors related to drug
absorption” Applied Biopharmaceutics and
Pharmacokinetics, Prentice Hall
International, INC., Stanford 1999, Page No. 99-128
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