A ppt on Drug absorption. Intended for Ayurveda UG and Dravyaguna PG students

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2. Fate of a drug
i. Absorption
ii. Distribution
iii. Metabolism
iv. Excretion
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3. Absorption
 Entry of a drug into the systemic circulation.
 Its movement among various body compartments
 Its distribution within the cell
 determined by the properties of a series of biological
membranes in the body.
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4. Bio-availability
Amount or % of drug that is absorbed from a given
dosage form and reaches the general circulation.
100% in c/o vascular administration
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5. Factors affecting Absorption and Bioavailability
 Factors affecting oral drug absorption and its
bioavailability
a) Drug related.
 Physical properties of the drug.
 Nature of the dosage form.
b) Patient related
 Physiological factors.
 Pharmacogenetic factors
 Disease states.
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6. Physical properties of the drug.
 Liquids > solids
 Crystalloids > colloids
 Aqueous > oily solutions - at site
 Oily solutions > Aqueous - at cell surface
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7. Dosage forms
 Particle size -
 Disintegration time and dissolution rate
 Formulation
 Eg - calcium and magnesium ions used as fillers reduce
the absorption of tetracycline
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8. Physiological factors.
 Ionization
 pH of the G.I fluid and the blood
 GI transit time:
 Area of the absorbing surface and local circulation
 Presence of other agents
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9. lonization:
 The mucosal lining of the GI tract is impermeable to
ionized form of weak organic acids and weak organic
bases.
 At the body pH, most drugs exist in two forms:
 (1) an unionized component,
 predominantly lipid soluble -cross the cell membrane
rapidly
 (2) an ionized, water soluble component.
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10. pH of the G.I fluid and the blood
 Weakly acidic drugs - rapidly absorbed from the
stomach
• (as they exist in the acidic medium of the stomach in an unionized
form)
 They act rapidly on oral administration
 e .g.,salicylates, Barbiturates
 However, most of the weakly acidic drugs are also absorbed
from the duodenum because of their solubility in the alkaline
medium and the large absorbing surface area
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11. pH of the G.I fluid and the blood
 Weakly basic drugs absorbed - in the small intestine
(in alkaline environment)
 The alkaline environment in which the drugs exist in
an unionized form, facilitates their absorption. Their
actions are delayed when administered orally
 e.g.pethidine, ephedrine
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12. pH of the G.I fluid and the blood
 At the pH values found in the intestine, the strongly
acidic or basic drugs are highly ionized and hence,
they are poorly absorbed.
 Aminogycosides are strong bases and hence their
absorption from GI tract is poor
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13. GI transit time
 Gastric emptying time altered by
 Presence of food
 Volume, viscosity & tonicity of the gastric contents
 (Rapid absorption occurs if the drug is given on empty
stomach )
 Increased peristalsis  dec absorption
 Structural alteration of GIT mucosa  dec
 Eg oedema
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14. GI transit time
 Food aids the absorption of
 Chloroquine
 Carbamazepine,
 Ribeoflavin etc
 Food interferes with the absorption of
 Ampicillin
 Aspirin
 Digoxin
 Levodopa etc.
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15. Area of the absorbing surface and local
circulation
 Drugs are absorbed better from the small intestine
than from the stomach
 because of the larger surface area.
 Reduction in the absorbing surface  reduces drug
absorption
 Eg – G.I. resection
 Increased vasularity can increase absorption.
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16. Presence of other agents
 Vitamin C increases the absorption of oral iron
 Phytates  retard it
 Absorption of fat-soluble vitamins reduced in the
presence of liquid paraffin
 Calcium (milk,antacids) + tetracyclin  insoluble
complexes  red absorption
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17. Disease states
 Absorption and first pass metabolism may be affected
in conditions like
 malabsorption,
 thyrotoxicosis,
 achlorhydria,
 cirrhosis of the liver,
 biliary obstruction etc
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18. Thank you
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