Seminar on

DEFINITION

“Absorption is defined as the process of movement of unchanged drug from the site of administration to the systemic circulation.”

MECHANISM OF DRUG ABSORPTION1) Passive diffusion and filtration2) Specialized transport A) Carrier- mediated transport i) Facilitated diffusion ii) Active transport a) primary active transport b) secondary active transport3) Phagocytosis4) Pinocytosis

Passive Diffusion It is defined as the

difference in the drug concentration on either side of the membrane.

Also called nonionic diffusion

It is the major process for absorption of more than 90% of the drugs.

The driving force for this process is the ‘concentration or electrochemical gradient’.

PORE TRANSPORT It is also called as Convective transport, Bulk flow

or filtration. The driving force for this process is the

‘hydrostatic pressure or the osmotic differences

across the membrane’. The process is important in the absorption of low

molecular weight, low molecular size drugs. Example: Urea, Water, Sugar

CARRIER-MEDIATED TRANSPORT The mechanism is thought to involve a

component of the membrane called as the carrier

that binds reversibly or non-covalently with the

solute molecules to be transported. The carrier may be an enzyme or some other

component of the membrane. Two types

Facilitated diffusion Active transport

FACILITATED DIFFUSION This mechanism

involves the driving force is concentration gradient.

In this system, no expenditure of energy is involved (down-hill transport), therefore the process is not inhibited by metabolic poisons that interfere with energy production.

ACTIVE TRANSPORT It is process where the

materials are transported across membranes against a concentration gradient.

The drug is transported from a region of lower to one of higher concentration i.e.. against the concentration gradient or ‘uphill transport’.

Examples : Sodium, potassium, iron, glucose and vitamins like niacin, pyridoxine and ascorbic acid.

ENDOCYTOSIS

Also called Corpuscular or Vesicular transport It involves engulfing extracellular materials within a

segment of the cell membrane to form a saccule or

a vesicle which is then pinched-off intracellularly. Includes two type of process:

Phagocytosis and Pinocytosis

PHAGOCYTIC UPTAKE OF MACROMOLECULES

PINOCYTOSIS

This process is important in the absorption of oil soluble vitamins & in the uptake of nutrients.

Aqueous solubility Concentration Area of absorbing surface Vascularity of absorbing surface Route of administration

References Essentials of Medical pharmacology by K.D

Tripathi pg;no 12-17. www.authorstream.com http://www.google.co.in/images

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