1. Presented By
Ishita Bajpai
Ist Mpharm
Department Of Pharmaceutics
Al Ameen College Of Pharmacy
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2. Absorption is the transfer of a drug from its site of administration to the
bloodstream.
The rate and efficiency of absorption depend on the route of
administration.
For IV delivery, absorption is complete=100 % bioavailability;
That Is, The Total Dose Of Drug Reaches The Systemic Circulation
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3. Absorption
The primary stage
involves food ingestion
•It starts from the oral
level , thereby food
enters the alimentary
tract , later it is
absorbed at
• 1. liver (Ist pass )
•2 stomach
•3 small
intestine(proteins )
•4 large intestine
•5 unabsorbed food
passes through
rectum, anal opening
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6. 10 . Gastric emptying
Factors affecting :-
i.Presence of food
ii.Nature of food i.e.
lipids/protein
iii.Viscosity of meal
iv.Volume of meal
v.Time of meal
vi.Presence of herbs
vii.Presence of chelating
agents /other drugs
viii.Git disorders like ulcer etc
ix.Emotional factors/
psychological influence
1.Local ph of gut
2.Contact time at the
absorption surface /transit
time
3.Surface area of gut
4.Blood flow to gut
5.First pass metabolism
6.Route of administration
7.Patient age.
8.Motility of intestine
9.Motility of
gut/gastrointestinal tract
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7. The pH increases gradually from mouth to colon and it
influences drug absorption in several ways.
Disintegration of some dosage forms depends upon pH.
Ex: Enteric coating formulations disintegrate in the
intestine and release their drugs in the intestine. They
do not disintegrate in the stomach.
Weakly acidic drugs dissolve rapidly in the alkaline pH
of the intestine. Whereas basic drugs dissolve rapidly in
acidic pH of the stomach. Since absorption follows
dissolution, and dissolution depends on pH, we can say
that pH influences absorption.
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8. If a drug moves through the GI tract very
quickly, as in severe diarrhea, it is not well
absorbed.
Conversely, anything that delays the transport
of the drug from the stomach to the intestine
delays the rate of absorption of the drug.
Absorption can be limited by the short transit
period of the drug through the small intestine
(2-4 hours).
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9. Time during which the drug is in proximity of
the absorbing gastrointestinal surface i.e.
from the stomach to the end of small
intestine is approximately 12 hours
Due to more favorable absorbing conditions
in upper intestine most drugs absorbed
better in upper intestine than in lower
intestine
10. Surface area available for absorption: Because
the intestine has a surface rich in microvilli, it
has a surface area about 1000-fold that of the
stomach; thus, absorption of the drug across
the intestine is more efficient.
Colon is usually a poor site of absorption due
to its low permeability and relatively low
surface area
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11. Blood flow to the intestine is much greater than the
flow to the stomach; thus, absorption from the
intestine is favored over that from the stomach.
Drugs administered intramuscularly or
subcutaneously are completely absorbed unless
destruction occurs at the site of administration or
during first-pass (e.g. for macromolecules such as
vaccines).
Absorption from these sites is highly dependant on
the blood flow at the site of injection.
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12. When drug absorbed across GIT, it enters
portal circulation before entering systemic
circulation.
If the drug is rapidly metabolized by the liver,
the amount of unchanged drug that reaches
systemic circulation is decreased.
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14. Route of administration
Oral i.e. enteral =slow absorption due to
number of steps
Per oral/parenteral (injections)= faster as
total quantity of drug enters systemic
circulation
Nasal=good and timely absorption
Topical= absorption is gradual and systematic
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15. Route Of
Administration: An
Illustration
Drugs inhaled orally directly
reach lungs .
Fewer steps of metabolism/
biotransformation
Drugs swallowed orally maybe
inactivated by liver and then
enter systemic circulation
Thus, more steps of
metabolism/ biotransformation .
Lesser extent of drug absorbed
in systemic circulation.
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16. Infants , neonates : slow absorption of drug
due to immature body organs and
underdevelopment of tissues , lack of
sufficient enzymes
Adolescents : improved absorption
Geriatrics : diminished absorption due to
depletion of enzymes .
Females absorb certain drugs better as
compared to males .eg steroids /hormonal
preparations
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17. Metformin is primarily absorbed from the
small intestine. The extent of metformin
absorption is improved when the
gastrointestinal motility is slowed.
Similarly drug absorption is decreased when
Motility of intestine is increased in case its
absorption is in intestine.
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18. Gastric Ulcer/duodenal ulcer slow down drug
absorption
Diseases like cirrhosis, retard drug absorption
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19. Metoclopramide is a prokinetic agent that
stimulates gastric emptying and GI transit .Its
mode of action appears to involve antagonism
of the inhibitory neurotransmitter dopamine,
and increase in acetylcholine release
Propantheline inhibits GI motility and diminishes
gastric acid secretion .It is used as an adjunctive
therapy in the treatment of peptic ulcer.
The rate and extent of absorption of many drugs
are affected by changes in GI motility
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20. Co-administration of drugs with food generally delays drug
absorption
Drug-food interactions studies has increased dramatically, and
many of the results of these studies have been unpredictable
and spectacular.
Drug may be affected differently by food when it is
administered in different formulations.
Drug-food interactions may be classified into five categories: those
causing reduced, delayed, increased, and accelerated absorption,
and those in which food has no effect.
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21. Rate of gastric emptying depends primarily
on caloric content of ingested meal i.e extent
of delay in gastric emptying is the same for
proteins ,fats, carbs provided their caloric
content is same
Since on molar basis the caloric content of
carbs , proteins, fats is different therefore
their rate of emptying is also different
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22. In general foods, especially fat, can slow gastric
emptying,
Carbs empty faster than proteins
Proteins empty faster than fats
That means 1 . carbs > 2. proteins > 3. fats empty in this
manner
Reason for slower emptying of fats is due to the fact
that fats form an oily layer at the top of chyme and
therefore digested more slowly by intestinal enzymes
Secondly :-fats promote secretions of bile which in turn
decreases gastric emptying. This effect is beneficial
for absorption of poorly soluble drugs eg griseofulvin
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23. Liquid meal empties faster from stomach.
Bulky or solid materials tend to be slower.
Increase in viscosity of gastric contents
reduces the rate of gastric emptying.
Therefore fluids pass through stomach very
quickly and solids remain until they are well
mixed with gastric juice and converted to liquid
state .
Increased viscosity delays stomach
emptying and hinder drug dissolution
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24. Since gastric emptying appears to follow first
order kinetics therefore as vol of meal
increase there is initial increase in the rate of
gastric emptying of gastric contents esp
when more fluid is present in stomach
the initial increase in rate of gastric emptying
is followed by a decrease in the rate of
emptying as the volume of gastric contents
decreases
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25. More volume more gastric emptying thus better
drug absorption and vice versa.
Gastric emptying of liquids in fasted state is a
function of volume.
For small volumes less than 100ml Gastric
emptying is slower and thus longer.
For large volume greater than 200 ml Gastric
emptying begins earlier ,around 10 minutes half
life .
Large volume of liquid in stomach help in drug
dissolution
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26. Empty stomach in the morning enhances
absorption of antacids.Eg :-
Ampicillin , Bethanechol, Captopril,
Rifampin, Sulfadiazine should be taken
empty stomach
Anti depressants , sedatives & hypnotics, anti
anxiety show enhanced absorption at night
Simvastatin(a hypolipidemic) is preferably
consumed at night
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27. The temperature of the meal should be same
as the temperature of the body 37.50c
Thus the temperature difference between
gastric food and drug should be minimum.
very hot meal/ warm food empties better
/faster from stomach than cold food
However when temp of ingested food
increases to body temp the rate of emptying
also increases
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28. REDUCE RATE OF GASTRIC
EMPTYING
Aspirin, anticholinergics
,narcotic analgesics and
ethanol
ACIDS in general reduce
rate of Gastric emptying
(the extent of reduction in
rate depends on conc. and
mol wt of acid )
Bile salts
ENHANCE THE RATE OF
GASTRIC EMPTYING
Alkalies eg NaHCo3
increase rate of gastric
emptying at lower conc.
But decrease at higher
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29. Effect of body posture :-
gastric emptying faster in supine position
and
Slower in lying position .
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30. Stress, depression
increase gastric
motility and rate of
gastric emptying
Sleeping on left side
delays gastric
emptying because the
gastric contents have
uphill task to empty
from the stomach
Vigorous exercise
decrease gastric
motility and rate of
gastric emptying
Sleeping on right
enhances due to
gravity facilitating in
emptying
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