This document discusses drug absorption through the gastrointestinal tract. It begins with an introduction and overview of the major routes of drug administration. It then describes the structure of cell membranes and the various mechanisms of drug transport across membranes, including both passive and active processes. Specific mechanisms discussed include diffusion, pore transport, ion-pair transport, and facilitated transport. The document focuses on drug absorption through the GI tract, outlining the three steps of transcellular transport and describing various passive transport processes. Finally, it discusses factors that can influence drug absorption through the GI, including physicochemical properties of the drug and various patient-related factors.

1. Presented By
Wazed Ali
B.Pharm 3rd Year 6th semester
Roll-20801920061
Subject-
BIOPHARMACEUTICS AND
PHARMACOKINETICS-PT616

2. ▪ INTRODUCTION
▪ ROUTES OF DRUG ABSORPTION
▪ CELL MEMBRANE STRUCTURE AND PHYSIOLOGY
▪ MECHANISMS OF DRUG ABSORPTION THROUGH GIT
▪ FACTORS INFLUENCING DRUG ABSORPTION THROUGH GIT
▪ REFFERENCES

3. ▪ Drug absorption is defined as the process of movement of unchanged drug from
the site of administration to systemic circulation.

4. ▪ Drugs administered by three major routes:
1. The Enteral Route : includes peroral i.e. Gastrointestinal, sub- lingual/buccal and
rectal routes. The GI route is the most common for administration of majority of
drugs.
2. The Parenteral Route;includes all routes of administration through or under one
or more layers of skin.While no absorption is required when the drug is
administered i.v., it is necessary for extravas- cular parenteral routes like the
subcutaneous and the intramuscular routes.
3. The Topical Route:includes skin, eyes or other specific mem- branes. The
intranasal, inhalation, intravaginal and transdermal routes may be considered
enteral or topical according to different definitions.

5. ▪ For a drug to be absorbed and distributed into organs and tissues and eliminated
from the body, it must pass through one or more biological membranes/barriers at
various locations. Such a movement of drug across the membrane is called as drug
transport.

6. There three broad categories are:
1. Transcellular/intracellular transport
A.PassiveTransport Processes
I. Passive diffusion
II. Pore transport
III. Ion- pair transport
IV. Facilitated or mediated diffusion
B.Active transport processes
I.Primary
II. Secondary
a. Symport (Co-transport)
b.Antiport (Counter transport)
2. Paracellular/Intercellular Transport
A. Permeation through tight junctions of
epithelial cells
B. Persorption
3. Vesicular or CorpuscularTransport
(Endocytosis)
A. Pinocytosis
B. Phagocytosis

7. ▪ It is defined as the passage of drugs across the GI epithelium.
▪ 3 steps involved in transcellular transport of drug-
1.Permeation of Gl epithelial cell membrane
2.Movement across the intracellular space (cytosol).
3.Permeation of the lateral or basolateral membrane.

8. ▪ PassiveTransport Processes –
These transport processes do not require energy
other than that of molecular motion (Brownian motion) to pass through the lipid
bilayer. Passive transport processes can be further classified into following types –
I. Passive diffusion
II. Pore transport
III. Ion- pair transport
IV. Facilitated or mediated diffusion

9. ▪ Also called non-ionic diffusion, it is the major process for absorption of more than
90% of the drugs.
▪ The driving force for this process is the concentration gradient.
▪ Passive diffusion is best expressed by Fick’s first law of diffusion,
which states that the drug molecules diffuse from a region of
higher concentration to one of lower concentration until equilibrium is attained and
that the rate of diffusion is directly proportional to the concentration gradient across
the membrane.
Adolf Fick (1829–1901)

10. ▪ The drug moves down the concentration gradient indicating downhill transport.
▪ The process is energy-independent and non-saturable.
▪ The rate of drug transfer is directly proportional to the concen- tration gradient
between GI fluids and the blood compartment.
▪ Greater the area and lesser the thickness of the membrane, faster the diffusion;
thus, more rapid is the rate of drug absorption from the intestine than from the
stomach.
▪ The process is rapid over short distances and slower over long distances.
▪ Equilibrium is attained when the concentration on either side of the membrane
becomes equal.

11. ▪ Also known as convective transport, bulk flow or filtration. Important in the
absorption of low mol.Wt. (less than 100).Low molecular size (smaller than the
diameter of the pore) & generally water-soluble drugs through narrow, aqueous
filled channels or pores in the membrane structure.E.g. Urea, water & sugars.
▪ The driving force for the passage of the drugs is the hydrostatic or the osmotic
pressure difference across the membrane.

12. ▪ Absorption of drugs like quaternary ammonium compounds (+) and sulphonic acids (-),
which ionise (convert into molecules) under all pH conditions is known as ion-pair
transport.
▪ Such neutral complexes have both the required lipophilicity as well as aqueous
solubility for passive diffusion. Such a phenomenon is called as ion-pair transport.

13. ▪ • It is a carrier-mediated transport system that operates down the concentration
gradient (downhill transport) but at a much a faster rate than can be accounted by
simple passive diffusion.
▪ The driving force is concentration gradient (hence a passive process). Since no
energy expenditure is involved, the process is not inhibited by metabolic poisons
that interfere with energy production.

14. ▪ This transport process requires energy from ATP (Adenosine triphosphate) to move
drug molecules from extracellular to intracellular.
▪ These are two types-
I. Primary
II. Secondary
a. Symport (Co-transport)
b. Antiport (Counter transport)

15. ▪ Primaryactive transport -In this process, there is direct ATP requirement.
Moreover, the process transfers only one ion or molecule and in only one direction,
and hence called as uniporter e.g. Absorption of glucose.
▪ Secondary active transport – In these processes, there is no direct requirement of
ATP ie. It takes advantage of previously existing concentration gradient.
It’s has two types-
a. Symport (Co-transport)
b. Antiport (Counter transport)

16. A. Physicochemical factors:
1. Drug solubility& dissolution rate
2. Particle size& effective surface area
3. Polymorphism& amorphism
4. Pseudoploymorphism(hydrates/solvates)
5. Salt form of the drug.
B. Pharmaceuticalfactors:
Disintegration time (tablets/capsules)
▪ Dissolutiontime
▪ Manufacturing variables
▪ Pharmaceutical ingredients (excipients/adjuvants)
▪ Nature & type of dosage form
▪ Product age & storage condition
C. Patient related factors:
1) Route of administration
2) Membrane physiology
a) Nature of cell membrane
b) Transport processes
3) Age
4) Gastric emptying time
5) Intestinal transit time

17. ▪ Bio pharmaceutics and Pharmacokinetics-A Treatise, By D. M. Brahmankar and
Sunil B.Jaiswal,Vallabh Prakashan Pitampura, Delhi .ISBN81-85731-03-9