The document discusses excretion and pharmacokinetics. It defines excretion as the removal of drugs from the internal to external environment and pharmacokinetics as how the body processes drugs. The major routes of drug excretion are through the kidneys, colon, lungs, sweat, saliva and breastmilk. The rate and route of excretion determines the dosage and frequency of drug administration. Drugs can be excreted through first or zero order kinetics, with first order kinetics being proportional to drug concentration and half-life. Several factors like age, disease states, drug interactions and urine flow can influence drug excretion rates.

1. ABBOTTABADCAMPUS.
ASSIGNMENT: 03.
TOPIC: EXCRETION AND IT’S DETAIL.
COURSE TITLE: PHARMACOLOGY AND THERAPEUTICS.
SUBMITTED TO: DR. Abdul jabbar Shah.
SUBMITTED BY: SYED JUNAID SHAH.
REGISTRATION: FA18-PHM-099.

2. DATE OF SUBMISSION: 24 OCT,2019.
Pharmacokinetics:
Meaning:
Pharmacomean drugwhile kineticsmeansputinmotion.
Definition:
Pharmacokineticsisthe discipline of pharmacologythatdealswiththe puttingof drugsinmotion.
Five ways by which body put drugs into motion:
1. Liberationof drugsfromdosage form
2. Absorption
3. Distribution
4. Metabolism
5. Excretion

3. Importance of pharmacokinetics:
It helpsthe physiciantodecide aparticulardrugfor a particulartime.
o Exertionof drugs:
Definition:
The processby whichdrugssubstancesare removedfrominternal toexternal environmentiscalled
excretionof the drugs.
OR
Excretionisthe passage outof systemicallyabsorbeddrugorit’smetabolites.
 Drugs may be excretedunchargedorafter biotransformation.
 Excretionandeliminationare not the same terms.
Eliminationof drugs:
DEFINITION:

4. Eliminationisthe breakdown(metabolism) plusexcretion.
Routes of excretion:
A. Major organs:
1. Kidneys:
Kidneyisthe mostimportantorganfor excretionof drugs.
2. Colon:
Unabsorbedportionorfrom bile drugs are excretedthroughthisroute.
3. Lungs:
Volatile drugs,alcohol,general anestheticsandparaldehyde all theseare excretedbythisroute.
B. Minor Routes:
1. Saliva.
2. Sweat.
3. Breastmilk.
4. Skin.
Importance of knowing route of excretion:
The route of excretion of drugsdeterminedose andfrequencyof administration.Clearanceisameasure
of drugelimination.Itisthe volume of plasmaclearedof the druginunittime,expressedasml/minute.
 Kinetics andExcretion:
Kineticsof clearance followseitherfirst orderkineticsorzeroorderkinetics.
a. First order kinetics:
 Majority of the drugs follow first order kinetics.
The term first order kinetics indicates that the rate of elimination is proportional to the
concentration.
 Drugs which follow first order kinetics have a characteristic half-life of
elimination.
 The drug in the blood will decrease by 50% for every half-life.

5. b. Zero order kinetics:
The term zeroorderkineticsimpliesthatthe rate of eliminationisconstantregardlessof
concentration.
 Drugs do not have constant half-life.
 Concentration of drug in plasma decrease in a linear fashion over time.
 Examples:
 Alcohol
 Phenytoin
 Salicylates.
1. Renal excretion:
Drugs differ n the way in which the kidney handle them.
Example:
Penicillin is cleared completely by a single passage whereas chlorpropamide is cleared very
slowly.

6. Basic principles involved in renal excretion:
I. Glomerular filtration.
Water soluble and polar compounds are unable to diffuse back into circulation and
are excreted.
II. Active tubular secretion.
Drugs such as organic acids e.g. penicillin, bases, quinine are transported by these
systems.
III. Passive diffusion across tubular epithelium.
The non-ionized form of weak acids and bases undergoes reabsorption.
Examples of drugs excreted through renal excretion:
o Penicillin
o Uric acid
o Probenecid
o Dopamine.
2. Hepatic excretion:
The endothelium of hepatic blood sinusoids behaves like a porous membrane and drugs
rapidly reach the hepatic extracellular fluid from the plasma.
From here through bile and through intestine drugs are excreted.
Examples:
o Digoxin
o Ampicillin
o Chlorpromazine.
3. Pulmonary excretion:
Volatile substances, irrespective of their route of administration can be excreted by
lungs.
Examples:
Poorly soluble gases like nitrous oxides are excreted by this route very quickly.
4. Sweat and saliva:
These two body fluids are the route of excretion for a few drugs.
The pKa and pH are the factors which regulate such secretion.
Examples:
o Bromide
o Iodide
o Metronidazole
o Phenytoin

7. 5. Excretion in milk:
Most drugs are transported from plasma of mother to the fetus through milk that will
be damaging to the fetus.
Examples:
o Beta blockers
o Dapsone
o Salicylates
o Doxepin.
Factors affecting excretion:
a. Physicochemical properties:
Physicochemical propertiesof drugsinfluence the rate of excretion.
e.g.: drugswithmolecularweightlessthan300 is excretedbykidneywhiledrugweightb/w
300 and500 are excretedbybothbile andurine
b. Binding characteristics:
Drugs that bindwithplasmaproteins cannotbe filteredbyglomerulusthusonlythose drugs
appearin filtrate thatare unboundor free.
c. Biological factors:
i. Age
ii. Sex
iii. Strain difference
All the affect the rate of excretion.
Example:
GFR is reducedinoldage due to whichexcretionof drugisprolong.
d. Blood flow to kidneys:
Bloodflowtokidneysenhancesthe eliminationof drugs.
e. Urine flow rate:
Urine flowrate enhancesthe eliminationwhichisincreasedbyforceddiuresisandlarge
fluidintake.
f. Drug interaction:
Anydrug interactioncan affectthe eliminationof drug.
e.g.:alkalizationof urine withcitratesandbicarbonatespromote the excretionof acidic
drugs.
g. Disease state:
Renal dysfunctionanduremiaare the diseasesthataffectthe eliminationof drugs.

8. END