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1. EXCRETION OF DRUGS
Dept. of Pharmaceutics
SREE DATTHA INSTITUTE OF PHARMACY,
Hyderabad, 501510.
Under the guidance of
Asst Professor Naga Chandrika,
M.Pharm
SREE DATTHA INSTITUTE OF PHARMACY 1
Submitted by:
K.SANDHYA
16U21R0014
B.Pharmacy 4th Year
2. ● Excretion is a process where by drugs/metabolites are
irreversibly transferred from the internal to the external
environment. OR
● Excretion is the passage out of systemically absorbed drug.
● Principal organs involved
- Kidneys
- Lungs
- Biliary system
- Intestines
- Saliva
- Milk
2SREE DATTHA INSTITUTE OF PHARMACY
3. Types of excretion:
RENAL excretion
NON-RENAL excretion
1. Biliary excretion
2. Pulmonary
excretion
3. Salivary excretion
4. Mammary excretion
5. Dermal excretion
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4. RENAL EXCRETION
❑Kidney is the primary organ of removal for most
drugs especially for those that are water soluble
and not volatile.
❑The three principal processes that determine the
urinary excretion of a drug
1.glomerular filtration,
2.tubular secretion, and
3.Tubular reabsorption (mostly passive back-
diffusion)
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5. a) Glomerular Filtration
● The ultrastructure of the glomerular capillary wall is such that it
permits a high degree of fluid filtration while restricting the
passage of compounds having weights relatively large molecular
● This selective filtration is important in that it prevents the filtration
of plasma proteins (e.g., albumin) that are important for
maintaining the plasma volume.
● Several factors, including molecular size, charge, and shape,
influence the glomerular filtration of large molecules
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6. •As the ultrafiltrate is formed, any drug that is free in the plasma water,
that is, not bound to plasma proteins or the formed elements in the blood
(e.g., red blood cells), will be filtered as a result of the driving force
provided by cardiac pumping.
•All unbound drugs will be filtered as long as their molecular size,
charge, and shape are not excessively large.
•Compounds with 20 Å to 42Å may undergo glomerular filtration
•GFR normally is 120 ml/min
•GFR declines progressively after the age of 50 and also low in renal
failure.
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7. b) Active Tubular Secretion
● Many drugs which do not enter into GF but do so by tubule
secretion which mainly occurs in proximal tubules
● It is carrier mediated process which require energy for
transportation of compounds against the conc. Gradient.
● Mainly 2 secretion mechanism are identified:
● 1) system for secretion of organic acids/anions-
eg. Penicilline, salicylates.etc
● These active secretory systems are important in drug excretion
because charged anions and cations are often strongly bound to
plasma proteins and therefore are not readily available for
excretion by filtration
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8. Organic Anion Transport Organic Cation Transport
Acetylcholine Acetazolamide
Bile salts Atropine
Furosemide Dopamine
Penicillin G Morphine
● Active secretory systems can rapidly and efficiently remove many
protein-bound drugs from the blood and transport them into tubular
fluid
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9. c) Active Tubular Reabsorption
● Some substances filtered at the glomerulus are reabsorbed by
passive diffusion and depends on the lipid solubility and ionization
of drug at the existing urinary pH.
● So lipid soluble drugs filtered from GF but 99% of the drug is
reabsorbed but non-lipid soluble and highly ionized drugs are
unable to do so.
● Active reabsorption is particularly important for endogenous
substances, such as ions, glucose, and amino acids, although a
small number of drugs also may be actively reabsorbed
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10. Clinical Implications of Renal Excretion
● The rate of urinary drug excretion will depend on the drug's
volume of distribution, its degree of protein binding, and the
following renal factors:
1.Glomerular filtration rate
1.Extent of active tubular secretion of the compound tubular
1.Possibly, extent reabsorption of active
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11. 1)Biliary Excretion/Faeces:
● Bile juice is secreted by the hepatic cells of the liver(steady flow-
0.5 to 1 ml/min) is important for the digestion and absorption of
fats
● Greater the polarity better the excretion so metabolites are more
excreted than parent compound
● Generally large molecules ar(MW 300)are elimated by bile
● Some drugs which are excreted as glucuronides are hydrolysed
by intestinal/bacterial enzymes to the parent drug which are
reabsorbed(enterohepatic cycling) and ultimate
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13. Drugs that Undergo Enterohepatic Recirculation
Adriamycin Methadone
Amphetamine Metronidazole
Chlordecone Morphin
Estradiol Sulindac
● Extensive enterohepatic cycling may be partly responsible for
persistence in the body
● Orally administered activated charcoal and/or anion exchange
resins have been used clinically to interrupt enterohepatic cycling
drugs the and in trap gastrointestinal tract.
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14. PULMONARY EXCRETION
● Gases and other volatile substances are eliminated by lungs,
irrespective to their lipid solubility
.
● Alveolar transfer of the gas/vapour depends on its partial pressure
in the blood.
❖ Eg: Alcohol, general anaesthetics
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15. EXCRETION IN OTHER BODY FLUIDS
★ Sweat and Saliva:
●Minor importance for most drugs
★ Saliva:
●un-ionized lipid-soluble form of the drugs are excreted passively
●Thus, the bitter after taste in the mouth of a patient is an indication of
drug excretion
●Substances excretion into saliva are usually swallowed, and therefore
their fate is the same as that of orally administered.
●Eg:caffeine, metronidazole, alcohol etc.
★ Sweat:
● Drugs or their metabolites that are excreted into
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16. Milk:
● Milk consists of lactic secretions which is rich in fats and proteins
with pH 7.0
● 0.5 to 1 litre of the milk is secreted in lactating mothers
● Low-molecular weight un-ionized water-soluble drugs will diffuse
passively across the mammary epithelium and transfer into milk
● However, the total amount of the drug reaching to the infant
through breast feeding is generally small and majority of the drugs
can be given to lactating mother without ill effects on infant
but some are contraindicated that should be avoided.
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17. Clearance (CL)
● It's a theoritical volume of plasma from which the drug is
completely removed in unit time
● CL=rate of elimination/ C CL
● C plasma concentration
❖ Eg: creatinine Clearance
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