2. BIOLOGICAL FACTORS
• Gastro intestinal physiology.
• Gastro intestinal blood flow.
• Gastro intestinal PH.
• Gastric emptying.
• Effect of food/GI content on drug absorption.
• Mal absorption.
• Disease State.
• First pass effect.
3. Gastro Intestinal Physiology
STOMACH • It is a pouch like
structure lined by
smooth epithelial
membrane.
• Absorption of weekly
acidic drugs or un
ionized drugs and week
basic drugs takes place.
4. Small intestine
generally carrier
mediated transport is
seen in most drugs.
Proximal part-absorption
of dietary constituents
includes mono
saccharides, AA, vits,
minerals etc.
Ileum-Vit B12, bile salts.
5. • The effective surface area
Micro villi can be made 10 times larger
to that of stomach because
of the presence of micro
villi.
• These are finger like
projections arising from and
forming folds in intestinal
mucosa.
• ESA was decreasing from
proximal part to distill part
of small intestine.
6. • ESA is less.
Large intestine • It is not an effective site
• Incomplete absorption
occurrs when large amount
of drug reaches colon
• Its an area of absorption
of escaped drug
• It is recommended for
certain drugs whose
metabolism occurred by
intestinal bacteria for bio
activation.
7. BLOOD FLOW
• It plays a major role in absorption by
continuously maintaing the concentration
gradient across the epithelial membrane.
• Absorption of polar molecules doesn’t depends
on the blood flow.
• rate of drug absorption is un effected by
mesenteric blood flow.
• Absorption of lipid soluble molecules highly
depends on the blood flow.
• Enter blood liver systemic circulation
8. Gastro intestinal PH
• PH varies according to the site.
• Many drugs are week organic acids or bases so
PH is the imp factor.
• Gastric fluid retards week basic drugs.
and promotes weekly acidic drugs.
• Gastric secretions having PH less than 1.
• It varies because of diet and dilution.
• Some drugs (penicillin) under goes degradation
because of PH, this can be rectified by pro drug
preparation.
• ex: penicillin-------------carindacillin
erythromycin--------erythromycinesfolate
9. Gastric emptying
• The passage of food from the stomach to the
small intestine is called gastric emptying.
• This process increases the bioavailability of the
drug because mostly the absorption occurs in
small intestine.
• Slow gastric emptying can delay the onset of
effect of the drug Ex: Analgesics& sedatives
10. GASTRIC EMPTYING IS
RECOMENDED
WHEN
• Rapid onset of action is desirable.
ex: sedatives
• Dissolution of drug occur in the intestine.
ex: enteric coated dosage forms.
• Which are not suits to gastric fluids.
ex:pencillin and erythromycin.
• Drug is best absorbed from the distal part of the
small intestine.
ex: Vit B12
11. Delayed gastric emptying is recommended
WHEN
• Food promotes drug dissolution and absorption.
ex: gresiofulvin
• Drugs irritate gastric mucosa.
ex: aspirin, phenyl butazone.
• Drugs are absorbed from the proximal part of
the SI & prolonged drug absorption site is
desired. Ex:VitB12&C
13. Effect of food on drug absorption
• Food has an unpredictable effect which is irreversible.
• Food stimulate hepatic blood flow, which have implication for
the bioavailability of the drug.
• Food tends to decrease the rate of gastric emptying which
effects drugs like penicillin
• Forms poorly soluble and un absorbable complexes.
• High protein food causes poor absorption of drugs. ex:
levodopa.
• High fat food causes poor absorption of drugs.
ex:isotertinonin.
• Administration of drug with large fluid volume enhances the
dissolution rate and gastric emptying.
14. Mal absorption
• It is a disorder with impaired absorption of fat,
protein, carbohydrate, vitamin, minerals& water.
• Drugs which induce mal absorption
Neomycin.
Phenytoin.
Amino salicylate
• These drugs mainly damages the gastro intestinal
epithelium emphasis the function of mucosa to serve
as a barrier to large polar molecule.
