BRIEF EXPLANATION OF PATIENT RELATED FACTORS AFFECTING DRUG ABSORPTION.

1. K VINAY
PHARMA D (PB)

2. •Process of
movement of
unchanged drug
from the site of
administration to
systemic circulation
ABSORPTION

3. Age
Gastric
emptying
time
Intestinal
transit
time
Include factors relating to the
•Anatomic, Physiologic and Pathologic
characteristics of the patient.

4. Gastrointestinal
pH
Disease
states
Blood flow
through the
GIT
Contact
Time of
Drug with
Gastrointes
-tinal
Mucosa

5. • Other Drugs
• Food
• Fluids
• Other Normal GI Contents
Gastrointestinal
contents
• Luminal Enzyme
• Gut wall Enzyme
• Bacterial Enzyme
Presystemic
Metabolism

6. INFANTS
• High gastric pH
• Low intestinal
surface & and
blood flow in GIT
ELDERLY PERSON
• Altered gastric
emptying
• Low intestinal
SA &GI blood
flow
• Risk of
achlorhydria &
bacterial
overgrowth in
small intestine
AGE

7. • The passage from stomach to small intestine
• Rate limiting step
• Major site of drug absorption
Gastric
Emptying
Parameters to quantify gastric emptying
1.Gastric emptying rate:
Speed at which the stomach contents empty into stomach
2.Gastric emptying time:
Time req. for gastric contents to
empty into small intestine..
3.Gastric emptying:
t1/2 is the time taken for half
the stomach contents to empty.

8. Factors
influencing
Gastric
emptying
Volume
of meal
Composition
of meal
Physical
state of
meal
Temperature
of meal
GI pH
Electrolytes
&osmotic
pressure
Body
posture
Emotional
state
Exercise
Disease
states
Drugs

9. • Small intestine is the major site
for absorption of most drugs
Intestinal
Transit :
Intestinal region Transit time
Duodenum 5 minutes
Jejunum 2 hours
Ileum 3 to 6 hours
Cecum 0.5 to l hour
Colon 6 to 12 hours

10. • A tremendous 10^7 fold diff. in the
hydrogen ion conc. observed b/w
gastric &colon fluids
Gastrointestinal
pH
GI pH
influences
drug
absorption
Disintegration
Dissolution
Absorption
Stability

11. • Several disease states can influence
the rate &extent of absorption.
Disease
states
GI Diseases
• Altered GI
motility
• GI Diseases&
infections
• GI surgery
CV DISEASES
• Congestive
cardiac
failure
HEPATIC
• Heptic
cirrhosis
• Hepatic
metabolism
Three major class of disease states that can influence the absorption:

12.  The GIT is extensively supplied by blood capillary network and the
lymphatic system
 The absorbed drug can thus be taken up by the blood or the lymph.
 Since the blood flow rate to the GIT (splanchnic circulation) is 500 to
1000 times (28% of cardiac output) more than the 'lymph flow, most
drugs reach the systemic circulation via blood whereas only a few
drugs, especially low molecular weight, lipid soluble compounds are
removed by lymphatic system.
 The high perfusion rate of GIT ensures that once the drug has crossed
the membrane, it is rapidly removed from the absorption site thus
maintaining the sink conditions and concentration gradient for
continued drug absorption.

13. •Other Drugs
•Food
•Fluids
•Other Normal GI Contents
GI Contents
A) Food-drug interactions:
Decrease of
drug absorption
Delayed gastric emptying affects by decreasing
drug stability.eg. penicillin
Formation of poorly absorbable complex
Increased viscosity preventing drug
dissolution.
Increased drug
absorption
Increases dissolution time for poorly
soluble drug.
Enhanced solubility due to GI secretions
like bile.
Prolonged residence time & absorption site
contact of the drug
Increased lymphatic absorption

14. B) Fluid volume
• Increased fluid
volume results :
• Better dissolution
• Rapid gastric
emptying
• Enhanced
absorption
C) Normal GI
Constituents
• GIT contains normal
constituents mucin,
bile salts &
enzymes.
• Eg. Mucin reacts
with streptomycin
&certain quaternary
cpdand retards its
absorption

15. Adsorption
Complexation
pH Change
Decreased GI
Transit
Increased
Gastric
Emptying
Altered GI
Metabolism
D) Drug-Drug interactions in the GIT :

16. • If drug moves very
quick through
GIT(severe diarrhoea)
absorption decreases
• If the movement of
drug from stomach to
intestine delays, it
delays the absorption.
• Lipophillic drugs are
best absorbed along
with food
Contact Time of
Drug with
Gastrointestinal
Mucosa

18. Decreased
Absorption
Destabilization
First
pass/presystemic
Metabolism
• The loss of drug. through biotransformation by such eliminating organs during·
its passage to systemic circulation

19. Luminal Enzymes
Digestive Enzymes Bacterial Enzymes
It contains hydrolases
which hydrolyse ester
containing drugs
(chloramphenicol)
Such drugs can be
administered through
colon
The GI microtlora is .
scantily present in
stomach , and small
intestine and is rich in
colon
The colonic microbes
render a drug active
biotransformation for
example sulfasalazihe

20. Gut Wall Enzymes
•Present in stomach, intestine and colon.
•Intestinal mucosa contains both phase I
and phase II (predominant) enzymes
•Alcohol dehydrogenase (ADH) is an
enzyme of stomach .mucosa that
inactivates ethanol.

21. 21
CONCLUSION
• Overall all these factors sum up to
decrease the absorption of the drug
which in turn leads to the decrease
in bioavailability, impacting an
efficient Therapeutic effect.

22. Reference:
-Biopharmaceutics and
pharmacokinetics; D M Brahmankar,
Sunil B. Jaiswal; Third Edition.
-Web.