Note introduction to pharmacology

INTRODUCTION
TO
PHARMACOLOGY
BY:
Mrs. Babitha K Devu
Assistant Professor
SMVDCoN

Introduction
The word Pharmacology is derived from Greek
– pharmacon means drug and logos means
study or knowledge.
Understanding how a drug or a substance is
likely to modify the living system is the crux of
pharmacology. It is based on sound
understanding of principles of physiology and
pathology.
It is expected from nursing staff to be familiar
with the various systems of medicine being
practiced in contemporary world.

Terminologies
Pharmacology: Pharmacology is the science
that deals with the study of drugs and their
interaction with the living systems.
Drug: Drug is a substance used in the
diagnosis, prevention or treatment of disease.
It is derived from the French word – Drogue
means Dry herb.
Drug: (WHO) Drug is any substance or
product that s used or intended to be used to
modify or explore physiological systems or
pathological states for the benefit of recipient.

Terminologies
Adverse Drug Reaction: (WHO) A
response to a drug which is noxious and
unintended, and which occurs at doses
normally used in man for the prophylaxis,
diagnosis, or therapy of disease, or for the
modifications of physiological function.
Pharmacokinetics: In Greek – kinesis
means movement. Pharmacokinetics is
the study of the absorption, distribution,
metabolism and excretion of drugs, i.e
what the body does to the drug.

Terminologies
Pharmacodynamics: Pharmacodynamics is
the study of the effect of the drugs on the
body and their mechanism of action, i.e what
the drug does the body.
Pharmacovigilance: Pharmacovigilance is
the science relating to the detection,
assessment, understanding and prevention of
adverse effects or any other drug-related
problem.
Pharmacopeia: It is an authoritative book
containing a list of medicinal drugs with their
uses, preparation, dosages, formulas,
storage and analysis, etc. And the content is
approved by the regulatory bodies.

Terminologies
Clinical Pharmacology: It is a sub-discipline
of pharmacology dealing exclusively with the
effects of drugs in humans.
Experimental Pharmacology: It is a sub-
discipline of pharmacology dealing with
effects of drugs in animals or cell-lines or
tissues.
Therapeutics: Therapeutics deals with the
use of drugs in the prevention and treatment
of disease.
Toxicology: Toxicology deals with the
adverse effect of the drug and also the study
of poisons, i.e detection ,prevention and
treatment of poisoning.(In Greek - Toxicon

Terminologies
Chemotherapy: Chemotherapy is the use
of chemicals for the treatment of
infections.
Pharmacy: Pharmacy is the science of
identification , compounding and
dispensing of drugs .It also includes
collection , isolation, purification ,
synthesis and Standardization of medical
substances.

Sources of Drugs
Drugs are obtained from various sources.
Sources of drugs are as follows:
• There are four sources of drug:

Sources of Drugs
I. NATURAL SOURCES: Most primitive
and abundant.
• Drugs are obtained from the following
natural sources:
A)PLANTS, B) ANIMAL SOURCES,
C) MINERAL & D) MICROORGANISMS

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS: Following categories of drugs are
derived from roots, leaves or barks of plants:
a) Alkaloids
• These are nitrogenous heterocyclic bases,
which are pharmacologically active principles
of plants. They are composed of carbon,
hydrogen, nitrogen and oxygen. They are
bitter in taste and are often poisonous. These
are, therefore, used in small doses. They are
insoluble in water. However, they form salts
with acids which are soluble in water.

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS: Following categories of drugs
are derived from roots, leaves or barks of
plants:
a) Alkaloids: Some examples of alkaloids
and their sources are listed in the table:ALKALOID SOURCE
Atropine Atropa belladonna - Root
Quinine Cinchona - bark
Morphine Papavarum somniferum – Seed
pods

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
b) Glycosides: They are ether-like
combination of sugar moiety with non-sugar
moiety. They are called glycosides, if the
sugar moiety is glucose.
Sugar moiety is not essential for the
pharmacological activity but it governs the
pharmacokinetic properties of the glycoside.
In the body it may be removed to liberate
aglycone. Pharmacological activity resides in
the non-sugar moiety that is called aglycone
(orgenin). Some examples are digitoxin,
digoxin and ouabain.

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
c) Oils: They are liquids which are insoluble
in water. They are of three types and are
used for various medicinal purposes.
Essential oils
Fixed oils
Mineral oils

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
c) Oils:
 Essential Oils (or volatile oils): Essential oils are
obtained from leaves or flower petals by steam
distillation, and have an aroma. They have no
caloric or food value. They do not form soaps with
alkalis. They do not leave greasy stain after
evaporation. On prolonged stay, they do not
become rancid (foul smell). They are frequently
used as carminatives and astringents in mouth -
washes. Some of these oils are solid at room
temperature and sublime on heating e.g. menthol
and camphor. Other examples are clove oil,
peppermint oil, eucalyptus oil and ginger oil.

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
c) Oils:
 Fixed oils: They are glycerides of stearic, oleic and
palmitic acid. They are obtained from the seeds that
are present within the cells as crystals or droplets.
They are non-volatile and leave greasy stains on
evaporation. They have caloric or food value. They
form soaps with alkalis. On prolonged stay, they
become rancid. They do not have marked
pharmacological activity and have little
pharmacological use except castor oil (purgative) or
arachis oil (demulcent). They may be of vegetable
origin e.g. olive oil, castor oil, croton oil and peanut oil
or of animal origin. e.g. cod liver oil, shark liver oil and
lard.

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
c) Oils:
Mineral Oils: They are mostly petroleum
products and extracted by fractional
distillation. These are mixtures of
hydrocarbons of the methane and related
aliphatic series. These are extracted in
various consistencies - hard paraffin, soft
paraffin and liquid paraffin. Hard and soft
paraffins are used as vehicles for preparation
of ointments while liquid paraffin is employed

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
d) Gums: These are colloidal exudates from
plants which are polysaccharides chemically
and yield simple sugars on hydrolysis. Upon
addition of water, some of them swell or
dissolve or form adhesive mucilage or remain
unchanged.
• Uses:
• In gut agar and psyllium seeds act as
hydrophilic colloids and function as
bulk purgatives. Gum acacia and gum
tragacanth are used as suspending agents in
making emulsions and mixtures.

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
e) Resins: These are ill-defined solid
substances found in plants, and are
polymers of volatile oil. They are
produced by oxidation and
polymerization of volatile oils. They
are insoluble in water but soluble in
alcohol, chloroform and ether.
Examples: gum resins (asafoetida);
balsams (benzoin, tolu, peru).

Sources of Drugs
I. NATURAL SOURCES:
A- PLANTS:
f) Tannins: are non-nitrogenous phenolic
plant constituents which have an
astringent action.
Pyrogallol tannins are glycosides of glucose
that occur in oak galls.
Tannic acid is tannin that is obtained from
oak galls and is used for treating burns
and diarrhoea

Sources of Drugs
I. NATURAL SOURCES:
B-ANIMAL SOURCES
• Some animal sources continue to be
used to procure some modern drugs
because of cumbersome and expensive
procedures for the synthesis of such
chemicals.

Sources of Drugs
I. NATURAL SOURCES:
B-ANIMAL SOURCES
• For example:

Sources of Drugs
I. NATURAL SOURCES:
C-MICROBIOLOGICAL SOURCES
• Many life-saving drugs are obtained from
fungi, moulds and bacteria e.g. penicillin
from Penicillium notatum, chloramphenicol
from Streptomyces venezuelae,
grisofulvin (an anti-fungal drug) from
Penicillium griseofulvum, neomycin from
Streptomyces fradiae and streptomycin
from Streptomyces griseus.

Sources of Drugs
I. NATURAL SOURCES:
D-MINERAL SOURCES
• Minerals or their salts are useful pharmaco -
therapeutic agents.
• For example: Ferrous sulfate is used in iron
deficiency anaemia. Magnesium sulfate is
employed as purgative. Magnesium
trisilicate, aluminium hydroxide and sodium
bicarbonate are used as antacids for
hyperacidity and peptic ulcer. Kaolin
(aluminium silicate) is used as adsorbent in
antidiarrheal mixtures. Radioactive isotopes
of iodine, phosphorus, gold are employed for
the diagnosis/ treatment of diseases
particularly malignant conditions.

Sources of Drugs
II. SEMISYNTHETIC SOURCES
• Sometimes semi-synthetic processes are
used to prepare drugs when the synthesis of
drugs(complex molecules) may be difficult,
expensive and uneconomical or when the
natural sources may yield impure
compounds. In these situation this methods
plays an important role. Some examples are
semi synthetic human insulin and 6-
aminopenicillanic acid derivatives. Prepared
by chemically modifying substances that are
available from natural source improve to
improve its potency, efficacy and also reduce

Sources of Drugs
III. SYNTHETIC SOURCES
• At present majority of drugs used in clinical
practice are prepared synthetically, such as
aspirin, oral antidiabetics, antihistamines,
amphetamine, chloroquine, chlorpromazine,
general and localanaesthetics, paracetamol,
phenytoin, synthetic corticosteroids,
sulphonamides and thiazide diuretics.
• Since the pharmacological activity of a drug
depends on its chemical structure and
physical properties, more effective and safer
drugs can be prepared by modifying the
chemical structure of the prototype drug.

Sources of Drugs
III. SYNTHETIC SOURCES
Advantages of synthetic drugs are:
• They are chemically pure.
• The process of preparing them is easier
and cheaper.
• Control on the quality of the drug
is excellent.

Sources of Drugs
IV. BIOSYNTHETIC SOURCES (genetically
engineered drugs)
• This is relatively a new field which is being
developed by mixing discoveries from
molecular biology, recombinant DNA
technology, DNA alteration, gene splicing,
immunology and immunopharmacology.
Some of the recent developments are
genetically engineered novel vaccines
(Recombinex HB – a hepatitis-B vaccine),
recombinant DNA engineered insulins
(Humulin- human insulin) for diabetes and
interferon-alpha-2a and interferon-alpha-2b
for hairy cell leukaemia.

Classification of Drugs
Drugs can be categorized in a number of ways.
In pharmacology, a drug can be classified by
its chemical activity or by the condition that it
treats.
In general, drugs are classified based on
– Therapeutic classification
– Pharmacologic classification (based on
mechanism of action and mode of action)
– Chemical classification
– Legal classification (Controlled Substances,
Drug Schedules, and Teratogenic Risks)

Therapeutic classification:-
Therapeutic classification is defined as
drugs is organized based on their
therapeutic usefulness in treating
particular diseases.

Pharmacologic classification:-
A pharmacologic classification refers to the
way a drug works at the molecular, tissue,
and body system levels. The pharmacologic
classification addresses a drug’s
mechanism of action, or how a drug
produces its physiological effect in the body.

Chemical classification:-
The three basic types of drug names are
chemical, generic, and trade name.
 A chemical name is assigned using
standard nomenclature established by the
International Union of Pure and Applied
Chemistry (IUPAC). A drug has only one
chemical name, which helpful in predicting
a substance’s physical and chemical
properties. Example: Chemical name for
aspirin is 2-acetoxybenzoic acid.

 The generic name of a drug is assigned
by the U.S. Adopted Name Council.
Generic names are less complicated and
easier to remember than chemical names.
The Food and Drug Administration (FDA),
the official Pharmacopoeia, and the World
Health Organization (WHO), routinely
describe a medication by its generic
name.
It is also called nonproprietary name.

 Generic name

 A drug’s trade name is assigned by the
company marketing the drug. The name is
usually selected to be short and easy to
remember. The trade name is sometimes
called the proprietary or product or brand
name.

Legal classification:-
Some drugs are frequently abused or have a
high potential for addiction. According to law,
drugs that have a significant potential for
abuse are placed into five categories called
schedules. These scheduled drugs are
classified according to their potential for
abuse:
– Schedule I drugs have the highest potential
for abuse
– Schedule V drugs have the lowest potential
for abuse

Indian Schedules to the rules

A teratogen is a substance that has the
potential to cause a defect in an unborn
child during pregnancy. A small number of
drugs have been shown to be teratogenic,
either in humans or in laboratory animals.
Classification of teratogenic risk places
drugs into categories A, B, C, D, and X.

Anatomical Therapeutic Chemical
Classification System with Defined Daily
Doses (ATC/DDD)
The purpose of the ATC/DDD system is to
serve as a tool for drug utilization research in
order to improve quality of drug use.
The ATC classification system groups the
active medical substances according to the
organ or system on which they act and
according to their therapeutic, pharmacologic
and chemical properties. The DDD is a unit
of measurement and is linked to
the ATC code.

Pharmacokinetics
The study of mechanisms and factors
associated with the absorption, distribution,
metabolism, and excretion of drugs.
That is the movement of the drugs into, within
and out of the body. The four corner stones of
pharmacokinetics are:
 Absorption
 Distribution
 Metabolism
 Excretion of drugs
Absorption & Distribution are influenced by the
formulation.

Pharmacokinetics
 Absorption
Is the passage of drug through cell
membranes to reach its site of action.
All these processes involve passage of the
drug molecules across various barriers like the
intestinal epithelium, cell membrane & so on to
reach the site of action.
Mechanisms of drug absorption
1. Simple diffusion = passive diffusion.
2. Active transport.
3. Facilitated diffusion.
4. Pinocytosis (Endocytosis).

Pharmacokinetics
 Absorption
1. Simple diffusion/Passive diffusion.
This mechanism does not utilize energy. With
the help of concentration gradient across a
membrane separating two body compartments
where the drug moves from region of high
concentration to one of lower concentration.
water soluble drug (ionized or polar) is readily
absorbed via aqueous channels or pores in cell
membrane.
Lipid soluble drug (non-ionized or non polar) is
readily absorbed via cell membrane itself.

Pharmacokinetics
 Absorption
2. Active transport.
This mode of drug entry involves specific
carrier protein that spans the membrane.
This is energy dependent and is driven
by the hydrolysis of adenosine
triphosphate (ATP).

Pharmacokinetics
 Absorption
3. Facilitated diffusion.
Facilitated diffusion is a form
of facilitated transport involving the
passive movement of molecules along
their concentration gradient, guided by
the presence of another molecule –
usually an integral membrane protein
forming a pore or channel.

Pharmacokinetics
 Absorption
4. Endocytosis.
Endocytosis is the process of capturing a
substance or particle from outside the cell by
engulfing it with the cell membrane, and bringing
it into the cell.

Pharmacokinetics
 Absorption
4. Endocytosis.
There are three main kinds of endocytosis:
• Phagocytosis, or cellular eating, occurs when
the dissolved materials enter the cell.
The plasma membrane engulfs
the solid material, forming a phagocytic vesicle.
• Pinocytosis, or cellular drinking, occurs when
the plasma membrane folds inward to form a
channel allowing dissolved substances to enter
the cell. When the channel is closed,
the liquid is encircled within a pinocytic vesicle.

Pharmacokinetics
 Absorption
4. Endocytosis.
• Receptor-mediated endocytosis is an
extremely selective process of importing
materials into the cell. This specificity is
mediated by receptor proteins located on
depressed areas of the cell membrane
called coated pits. The cytosolic surface of
coated pits is covered by coat proteins. In
receptor-mediated endocytosis, the cell will only
take in an extracellular molecule if it binds to its
specific receptor protein on the cell’s surface.
Once bound, the coated pit on which the bound
receptor protein is located then invaginates, or
pinches in, to form a coated vesicle.

Pharmacokinetics
 Absorption
Bioavailability:
 Bioavailability refers to the rate and extent of
absorption of a drug from dosage form.
 It is a measure of the fraction (F) of administered dose
of a drug that reaches the systemic circulation in the
unchanged form. BA = Quantity of drug reaching
systemic circulation/Quantity of drug administered
oIV = 100%
oOral < 100%
oOther routes ≤ 100%
Example: Cyclosporine Bioavailability
IV = 100% , Oral = 25% . Therefore, oral dose = 4 x IV
dose.

Pharmacokinetics
 Absorption
Bioavailability:
Factors Affecting Bioavailability –
Molecular weight of drug.
Drug Formulation (ease of dissolution). (solution >
suspension > capsule > tablet)
Solubility of the drug
Chemical instability in gastric pH (Penicillin &
insulin )
First pass metabolism reduces bioavailability – it is
the metabolism of a drug during its passage from the
site of absorption to the systemic circulation.

Pharmacokinetics
 Absorption
Bioavailability:
Factors Affecting Bioavailability –
Area and vascularity of the absorbing
surface.
Rate of gastric emptying.
Intestinal motility (Transit Time)
• Diarrhea reduce absorption
Drug interactions
Presence of Food

Pharmacokinetics
 Absorption - Summary
 Most drug absorption occurs through passive
absorption.
 Lipid soluble drugs are more readily absorbed
than non-lipid soluble drugs.
 Non-ionized drugs are more readily absorbed
than ionized drugs.
 Weak acids or weak bases are more readily
absorbed in the small intestine than strong acids and
bases.
 Stronger acids can be absorbed in stomach.
 Most drug absorption occurs in the small
intestine.
 Large surface area

Pharmacokinetics
 Distribution
In this process drug reversibly leaves the blood
streams and enters the ECF and for the cell or
the tissue. Drugs will accumulate greatly in
adipose or fat tissue. Usually they are not active
in fat tissue; will slowly reenter the blood
streams.
Various factors determine the rate and extent of
distribution, they are lipid solubility, ionization,
blood flow/permeability of the barriers and
binding to plasma proteins and cellular protein.
Unionized and lipid soluble drugs are widely
distributed through out the body.

Pharmacokinetics
 Distribution
Plasma Protein Binding:
On reaching the circulation ,most of the drug bind
to plasma protein; acidic drug mainly bind with
albumin and basic drugs to alpha - acid
glycoprotein, lipoprotein and beta globulin. The
free or unbound fraction of the drug is the only
form available for action, metabolism and
excretion. The protein bound form serves as a
reservoir. Protein binding prolongs the duration
and action of drug. e.g warfarin 99%, morphine
35%, ethosuximide and lithium 0%.

Pharmacokinetics
 Distribution
Blood Brain Barrier:
The endothelial cells of the brain capillaries have
tight junctions. Moreover neuroglial cells
envelope the capillaries and together these
form the BBB. Only lipid soluble and unionized
drugs can cross BBB.
Tissue binding:
Some drugs get bound to certain tissue
constituent because of special affinity for them.
Tissue binding delays excretion and thus
prolongs the duration of drug.

Pharmacokinetics
 Distribution
Placental Barrier:
Lipid soluble ,unionized drugs readily cross the
placenta while lipid insoluble drugs cross to
a much lesser extent. Thus drugs taken by
the mother can cause severe unwanted
effects in the fetus.

Pharmacokinetics
 Distribution

Pharmacokinetics
 Metabolism/Biotransformation
It is the chemical alteration of the drug in the
body. It is a major mechanism for drug
elimination.
Metabolism or biotransformation is the process of
biochemical alteration of the drug in the body.
Body treats most of the drugs as foreign
substance and tries to inactivate and eliminate
them by various biochemical reactions. Theses
processes convert the drugs into more polar,
water soluble compounds so that they are
easily excreted through the kidneys. Some
drugs are excreted largely unchanged in urine,

Pharmacokinetics
Site of Metabolism:
Mainly drugs are metabolized in liver. However
some are metabolized in kidneys, lungs, gut
mucosa, blood and skin.
Result:
– Active drug to inactive metabolite. E.g. Morphine
– Active to more active metabolite. E.g. Digitoxin –
digoxin
– Inactive drug (Prodrug) to active metabolite.
E.g. levodopa – dopamine, cortisone -
hydrocortisone

Pharmacokinetics
Chemical Reactions/Process involved in Metabolism
The chemical reactions of biotransformation can take
place in two phases,
1. Phase I (Non-synthetic reactions /
Functionalization): Convert the drug to more polar
metabolite by oxidation, reduction, or hydrolysis. If
the metabolites are not water soluble it undergoes
phase II reactions.
2. Phase II (Synthetic/Conjugation reaction): In this
reactions water soluble substance present in the
body like glucuronic acid, sulfuric acid or an amino
acid combine with the drug to form a highly polar
compounds it excreted by the kidneys. Large
molecules are excreted through the bile.

Pharmacokinetics

Pharmacokinetics
Factors Influencing Metabolism:
 Genetic Differences (Level of enzymes)
oSpecies
oFamilial
 Physiological Status
oAge
oSex
oNutrition & Diseases
 Environmental Status
oStress
oRadiation
oEffect of chemicals

Pharmacokinetics
Excretion is the process of removing a drug
and its metabolites from the body. This usually
happens in the kidneys via urine produced in
them. Other possible routes include bile, saliva,
sweat, tears, breast milk and faeces.
The lungs are an excretion route by which
volatile lipophilic substances (e.g., inhaled
general anesthetics) can be excreted.
Most drugs are insufficiently polar (and,
therefore, water soluble) to be excreted directly.
Instead they need to metabolise to produce
more polar, water-soluble molecules

Pharmacokinetics
Renal excretion is quantitatively the most
important route of excretion for most drugs
and drug metabolites. Renal excretion
involves three processes: Glomerular
filtration, tubular secretion, and/or tubular
reabsorption.
Biliary excretion involves active secretion of
drug molecules or their metabolites from
hepatocytes into the bile. The bile then
transports the drugs to the gut, where the
drugs are excreted.

Pharmacokinetics
Pulmonary excretion is important for
gaseous lipophilic substances. The gaseous
general anesthetics are the most common
example. Drug diffuses from the plasma into
the alveolar space and is excreted during
expiration.
Breast milk is a quantitatively relatively minor
route of drug excretion. Nevertheless, it is
clinically important for breastfeeding mothers
and their infants. The baby will ingest drugs
excreted in the breast milk.

What the drug does to the body?
Pharmacokinetics
Pharmacodynamics
Dosage
Plasma
Concentration
Effect
s
Site of
Action

It deals with:
Mechanism of action
Adverse drug reaction
Drug-receptor interactions
Combined drug action

It deals with:
Mechanism of action: the drugs produce
their effects by interacting with the
physiological systems of the organisms. The
principle behind drug action are:
Stimulation: ↑ing activity of tissues
Depression: ↓ing activity of tissues
Irritation: Counterirritant
Replacement: Insulin in DM
Chemotherapy: Antibiotics/anticancer drugs
Modification of immune status

Mechanism of action:
Stimulation: Selective increase in activity of
specialised cells is termed as stimulation. Eg.
Adrenaline stimulates heart, pilocarpine
stimulates salivary glands.
Depression: This is selective decrease in the
activity of specialised cells. Eg. Quinidine
depresses heart, barbiturates depress CNS.
Irritation: It is the effect of drugs on growth,
nutrition & morphology of living tissues which
induces in inflammation, corrosion & necrosis
of the cells. Eg. Ionising rays, bleomycin.

Mechanism of action:
Replacement: Use of natural metabolites ,
hormones and their congeners in deficiency
states. Eg. Thyroxine in myxoedma, insulin in
DM.
Chemotherapy: It is either by bactericidal or
cytotoxic action. Selective anti infective or
cytotoxic action for parasites or cancer cells,
attenuating them without affecting the host
cells. Eg. Penicillin, Chloroquine, Zidovudine
Modification of immune status: Vaccines and
sera act by improving immunity while
immunosuppressant's acts by depressing
immunity. Eg. BCG, Glucocorticoids.

Site and Mechanism of Drug Actions:
The site of drug action means where a drug acts. It is
divided into two areas:
Drug which act only at the site of
administration. Eg. Ointments, local anaesthetics.
The drug will be absorbed into the
blood and act systemically. Once in the circulation
drugs may act by binding to different sites by
different mechanisms. Most drugs produce their
effects by binding to specific target proteins like

Mechanism of Drug Actions: The
fundamental mechanism behind how the
drug acts are as follows:
Non receptor mediated
Receptor mediated
Non receptor mediated actions
1. Physical action: The action could result from
its physical properties like Mass of drug -
Ispaghula husk, Adsorptive property - char
coal.

Mechanism of Drug Actions:
2. Chemical action: Drugs may act by their chemical
properties like acidity/alkalinity, chelating etc. Eg.
Antacids neutralise gastric HCl.
3. Through enzymes: Drugs may act by Inhibition of
various enzymes, thus altering the enzyme mediated
reactions. Membrane pumps like ATP, H+ may be
inhibited by drugs. Eg. Aspirin inhibits
Cyclooxygenase.Some drugs act also by
Stimulation which occurs commonly with
endogenous substances like hormones. Eg.

4. Altering the metabolic processes: Drugs like
antimicrobials alter the metabolic pathways in the
microorganisms resulting in the destruction of
microorganisms. Eg. Sulfonamides – interfere with
bacterial folic acid synthesis.
5. Through ion channels: Interfere with the
movement of ions across specific channels. Eg.
Calcium Channel blockers.

6. Placebo effect: Inert substance which is given in
the garb of medicine which works by psychological
rather than pharmacological means. Is often
responses equivalent to the active drug. Eg.
Types of Placebos: There are two types of placebos:
• Pure or inactive placebos, such as sugar pills or
saline injections
• Impure or active placebos, such as prescribing an
antibiotic for a viral infection or a vitamin even
though the patient doesn't need it

Receptor mediated actions
What is a receptor ?
Macromolecule or binding site located on the surface
or inside the effectors cell that serves to recognise
the signal molecule/drug and initiate response to it.
Itself has no function.

Different terminologies Used to Describe drug-
receptor interaction:
•Affinity: Ability of the drug to bind the receptor
•Intrinsic activity: Ability of the drug to elicit a
response after binding to a receptor
•Agonist: An agent which activates the receptor to
produce an effect similar to that of physiological
signal molecule
Has affinity + IA. Eg. Adrenaline on beta receptors

•Antagonist: Agent which prevents the action of an
agonist on a receptor and subsequent response.
Does not have any effect of its own
Affinity + No I.A. Eg. Propranolol on ß receptor
•Partial agonist: Binds to receptor but sub maximal
response Eg: Nalorphine
Affinity + sub maximal I.A.

•Inverse agonist: An agent which activates a receptor
to produce an effect in the opposite direction to that
of the agonist. Eg. ß - Carbolines
Affinity+ I.A with negative sign

When two or more drugs are given
simultaneously or in quick succession, they
may be indifferent or exhibit synergism or
antagonism.
The drug interaction is the alteration in the
duration or the magnitude of the
pharmacological effects of one drug by
another drug. This response can be greater
or lesser than the sum of their individual
effects.

The sites of drug interaction may be:
In vitro – This take place in the syringe before
administration. Eg. Penicillin & Gentamycin
should never be mixed.
In vivo – This occurs within the body after
administration.
The drug - drug interaction may be
Synergism
Additive
Supraadditive (Potentiation)
Antagonism

Synergism: Syn – together
Ergon – work
• They may act in same direction
• One may be inactive, but enhances others
action
Additive: Effect of combination is equal to the
individual effect of components
Effect of drugs A+B = Effect of drug A + Effect of
drug B
Eg. Aspirin + Paracetamol – analgesic/ antipyertic
Nitric oxide + Halothane – General anaesthetic

Supraadditive (Potentiation): Effect of
combination is greater than the individual
effects of components
Effect of drug A+B > Effect of drug A + effect of
drug B
Eg. Levodopa + Carbidopa – Inhibition of
peripheral metabolism
Antagonism: One drug decreases or inhibits
the action of other.

All drugs can produce unwanted effects.
Definition:
Any response to a drug that is noxious
and unintended and that occurs at doses
used in man for prophylaxis,
diagnosis/therapy.

Extent of the problem:
Any and every drug can cause ADR,s ADR- most
common cause of iatrogenic diseases Incidence
b/w 10-25% in diff clinical settings 3% to 5%
hospitalizations caused by ADR’s (300000 in USA).
In India serious effects were seen in 6.7% of
patients, a 2014 study reported. Other studies
have cited drug side effects as the reason for 3.4%
of hospital admissions in India, 3.7% hospital
readmissions, and 1.8% mortality. In the
developed world, adverse reactions are believed to
be the fourth-leading cause of death. Many of the

Grading of ADR
• Based on Severity
Minor – Moderate – Severe – Lethal
• Based on area affected
Local Vs Systemic
• Based on reversibility
Reversible Vs Irreversible

• Spectrum of Adverse Drug Reactions:
Side effects
Toxic effects
Intolerance
Iatrogenic Diseases
Drug dependence
Teratogenicity
Carcinogenicity and Mutagenicity
Others

Side effects: Are actions of drugs that are not
specifically desired in a treatment and are
exerted at therapeutic dose levels. Eg.
Constipation with morphine, hypoglycemia with
insulin.
Toxic effects (Toxicity): It can be either primary
or secondary effects.
– Primary toxic effects: Primary undesirable,
often serious adverse effects of the drugs occur
with over-dosage (absolute) or occur with

Toxic effects (Toxicity):
– Primary toxic effects: Eg. Morphine causes
respiratory depression, liver damage from PCM
over dose, Excessive pharmacological action of
the drug CNS depression with barbiturates
Bleeding with warfarin.
– Secondary effects: Indirect consequences of a
primary action of the drug. Eg. Coticosteroids
weaken host defence mechanisms latent TB
gets activated, Hypokalemia due to diuretics.

Intolerance: Characteristic toxic effects of
a drug in an individual at therapeutic
doses. It could be in the form of
– Idiosyncrasy: Inherent qualitative abnormal
reaction to a drug, usually due to genetic
abnormality. Eg. aspirin causing an attack of
asthma.
– Allergic reaction: An abnormal reaction of
the immune system to a medication. Also
called hypersensitivity. Eg. Antibiotics --

Iatrogenic Diseases: Also called physician induced
are disease caused by physician due to introduction
of some drugs. Eg. Blood transfusion, GI & Urinary
disturbances due to some antibiotics.
Drug dependence: A state in which the individual is
so dependent on the drug that the use of drugs for
personal satisfaction is accorded a higher priority
than other basic needs, despite known risks to
health. Ex. Cocaine, Amphetamines, Nicotine.
Drug withdrawal reactions: Sudden interruption of
therapy with certain drugs results in adverse
reactions Ex: Severe adrenal insufficiency with
abrupt cessation of corticosteroids

Teratogenicity: The capacity of a drug to cause
fetal abnormalities when administered to the
pregnant mother. Ex. Warfarin Retarded growth,
Phenytoin Cleft palate/Cleft lip.
Carcinogenicity and Mutagenicity: Refers to
the capacity of a drug to cause genetic defects
(mutagenicity) To cause cancer (carcinogenicity).
Others: It include photosensitivity, photo toxicity,
photo allergic reactions, hepatotoxicity etc.

Factors Affecting Drug Actions:-
Age:
Body weight:
Sex: hormonal effect and smaller body size may influence
women.
Species and race:
Diet and environment:
Route of administration:
Genetic factors:
Dose:
Disease:
Psychological factors:
Presence of other drugs:

Note introduction to pharmacology

Note introduction to pharmacology

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