2. EXCRETION OF DRUG:
O Drug excretion is the final step in the
ADME (Absorption, Distribution,
Metabolism and Excretion) process and
consists of a series of pathways that
remove an administered drug and or its
metabolites from the body.
O The major organ of excretion are the
kidneys, the intestine and the biliary
system and the lungs. Drugs are also
excreted in small amount in the saliva,
sweat and skin.
4. 1. Renal Excretion:
O Kidney is the most important organ of
drug excretion.
O The three process involved in the
elimination of drug through the
kidneys are glomerular filtration,
active tubular secretion and passive
tubular reabsorption.
5. Glomerular Filtration:
O Most drugs are filtered through glomerulus.
O Glomerulus filtration of drugs occurs
to:
1. Low molecular weight drugs.
2. Free form of the drug (unbound to the
plasma proteins) are filtered.
3. Water soluble drugs such as
Aminoglycosides.
6. Active Tubular Secretion:
O Occurs mainly in the proximal tubules.
O Many weak acid and weak bases are
actively secreted by the proximal tubules.
O Penicillin is an example for actively
secreted drug.
7. Passive Tubular Reabsorption:
O Occurs in the Distal convoluted tubules
and collecting ducts.
O Only lipid soluble drugs (unionized drugs)
undergoes passive tubular reabsorption
from the tubular lumen back to systemic
circulation.
10. BILIARY EXCRETION:
O Drugs such as Doxycycline, Morphine,
Indomethacin appear high concentration
in the bile.
O Such drugs may get reabsorbed from the
intestine and re-excreted in the bile
therefore exerting a prolonged action.
O This phenomenon of drug cycling between
intestine and liver is called Enterohepatic
circulation.
12. Gastrointestinal excretion:
O Unabsorbed portions of the orally
administered drug are eliminated through
the faeces.
O Drugs like purgatives are excreted
through this excretion.
14. PULMONARY EXCRETION
O The lungs are the main route of elimination for
gases and volatile general anesthetics and
drugs such as the paraldehyde and alcohol.
15. SALIVARY EXCRETION:
O Certain drugs like iodide and metallic salts are
excreted in the saliva.
MAMMARY EXCRETION:
O Drugs taken by the lactating women may
appear in the milk.
O They may or may not adversely affect the
baby.
O Examples: Aminoglycosides, Cephalexin and
Digoxin.
16. OTHER ROUTES OF EXCRETION:
SKIN:
O Metals like arsenic and mercury are
excreted through the skin.
SWEAT:
O Drugs like iodide, rifampicin and
heavy metals are excreted through
sweat.
17. Reference books:
O Pharmacology for Pharmacy students.,
Padmaja Udayakumar.
O Pharmacology and Pharmacotherapeutics.,
R.S.Satoskar, Nirmala N .Rege, Raakhi K.
Tripathi, S.D. Bhandarkar.
O Essentials of Medical Pharmacology., K.D.
Tripathi.
