Pharmacology Introduction for Nursing Students

2. INTRODUCTION TO PHARMACOLOGY
 DEFINITION:
 Pharmacology is the science that deals with the study of
drugs and their interaction with the living systems.
 The word Pharmacology is derived from Greek –
pharmacon means drug and logos means study.
 DRUG:
 Drug is a substance used in the diagnosis ,prevention or
treatment of disease.
 PHARMACOKINECTICS:
 Pharmacokinectics is the study of the absorption
distribution ,metabolism and excretion of drugs,i.e what the
body does the drug (in greek kinesis = movement).

3. INTRODUCTION TO PHARMACOLOGY
 DEFINITION:
 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.
 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.(Toxicon =poison in greek.

4. INTRODUCTION TO PHARMACOLOGY
 CHEMOTHERAPHY :
 Chemotheraphy is the use of chemicals for the treatment of
infections.the term now also includes the use of chemical to
treate malignancies.
 PHARMACY :
 Pharmacy is the science of identification , compounding
and dispensing of drugs .It also includes collection ,
isolation, purification , synthesis and Standardization of
medical substances.




5. SOURCES OF DRUGS
 The sources of drugs could be natural or synthetic ,
 NATURAL SOURCES:
 1.PLANTS,e.g Atropine ,Morphine ,Quinine
,digoxine,pilocarpine,physostigmine.
 2.ANIMALS e.g . Insulin ,heparin ,gonadotrophins and
antitoxic sera.
 3.MINERALS,Magnesium sulphate , Aluminium hydroxide
,iron ,sulphur and radio active isotopes.
 4.MICROORGANISMS ,Antibacterial agents are obtained
from some bacteria and fungi.we thus have
pencillins,cephalosporins,tetracycline and other antibiotics.

6. SOURCES OF DRUGS
 5.HUMAN: some drugs are obtained from man ,e.g
 Immunoglobulin from blood,growth hormone from anterior
pituitary and chorionic gonadotrophins from the urine of
pregnant woman.
 SYNTHETIC :
 Most drugs are now synthesized .e.g
quinolones,omeprazole,sulfonamides,pancuronium,neostigmi
ne.
 Many drugs are obtained from cell culture ,e.g urokinase from
cultured kidney cells.
 some are now produced by recombinant DNA technology ,e.g
human insulin, tissue plasmogen activator and some drugs by
Hybridoma technique, e.g monoclonal antibodies.

7. ROUTES OF DRUG ADMINISTRATION
 Drugs may be administered by various routes .the choice
of the route in a given patient depends on the properties of
the drug and the patients requirements.A knowledge of
advantage and disadvantage of the routes of drug
administration is essential.
 The route can be broadly divided into:
 Enteral
 Parenteral
 Local

8. ENTERAL ROUTE (ORAL INGESTION )
 This is the most common ,oldest and safest routes of drug
administration.the large surface area of the GI ,the mixing of its
content and the differences in pHat different parts of the gut help
effective absorption of the drugs given orally.
 ADVANTAGES:
 1.Safest route
 2.Most convenient
 3.Most economical
 4.Drugs can be self-administered
 5.Non-invasive route


9. DISADVANTAGES
 1.Onset of action is slower as absorption needs time.
 2.Irritant and unpalatable drugs cannot be administered.
 3.Some drugs may not be absorbed due to certain physical
characteristics, e.g streptomycin.
 4.There may be irregularities in absorption.
 5.Irritation to the GIT may lead to vomitting .
 6.Some drugs may be destroyed by gastric juices.e.g insulin.
 7.Cannot be given to unconscious and uncooperative patients.
 8.Some drugs may undergo extensive first pass metabolism in
liver.
 9.Patients may forget to take the tablet which is the practical
problem.

10. ENTERIC COATED TABLET
 Some tablets are coated with substances like cellulose-
acetate, phthalate,gluten,etc., which are not digested
by the gastric acid but get disintegrated in the alkaline
juices of the intestine.
 This will
 1.Prevent gastric irritation.
 2.Avoid destruction of the drug by the stomach.
 3.Provide higher concentration of the drug in the small
intestine.
 4.slow the absorption ,and there by prolong the
duration of action.

11.  ADVANTAGES :
 Frequency of administration may be reduced.
 Therapeutic concentration may be maintained for along
time specially when noctural symptoms are to be treated.
 DISADVANTAGES :
 It is more expensive.
 There may be releaes of the entire amount of the drug in a
short time leading to toxicity.

12. PARENTERAL ROUTE
 Routes of administration other than the enteral route are
known as parenteral routes.Here the drugs are directly
delivered into tissue fluids or blood.
 ADVANTAGES :
 Action is more rapid and predictable than oral
administration.
 These routes can be employed in unconscious or
uncooperative patients.
 Gastric irritant can be given parenterally and therefore
irritation to the GIT can be avoided.

13.  It can be used in patients with vomitting or those unable to
swallow.
 In emergencies parenteral routes are very useful.
 Digestion by the gastric and intestinal juices and the first
pass metabolism are avoided.
 DISADVANTAGES :
 Asepsis must be maintained.
 Injection may be painful.
 More expensive less safe and incovenient.
 Injury to nerve and other tissues may occur.

14.  Parenteral route include:
 1.Injections
 2.Inhalation
 3.Transdermal route
 4.Transmucosal route
 INJECTION
 Intradermal
 The drug is injected into the layers of the skin by:
 1.Raising a bleb ,e.g . BCG vaccine ,tests for allergy.
 2.By multiple punctures of the epidermis through a
drop of the drug, e.g. Smallpox vaccine.
 Only a small quantity can be administered by this
route and it may be painful.

15.  Subcutaneous (SC) injection
 Here the drug is deposited in the SC tissue ,e.g.insulin,
heparin.As this tissue is less vascular, absorption is
slow and largely uniform and this make the drug long-
acting.
 DISADVANTAGES :
 As SC tissue is richly supplied by nerves ,irritant drugs
cannot be injected.
 In shock absorption is not dependable because of
vasoconstriction.
 Repeated administration at the same site can cause
lipoatrophy resulting in erratic absorption.

16.  Drugs can also be administered subcutaneously as :
 1.Dermojet :
 In this method ,a high velocity jet of drug solution is
projected from a fine orifice using a gun . The solution
gets deposited in the SC tissue from where it is
absorbed .As needle is not required ,this method is
painless.It is suitable for vaccines.
 2.pellet implantation :
 Small pellets packed with drugs are implanted SC.The
drug is slowly released for weeks or months to provide
constant blood levels,e.g
,testosterone,desoxycortocosterone acetate.

17.  3.sialistic implants :
 The drug is packed in sialistic tubes and implanted SC .
The drug gets absorbed over months to provide constant
blood levels ,e.g .hormones and contraceptives. The
empty nonbiodegradable implant has to be removed.
 INTRAMUSCULAR:
 Aqueous solution of the drug is injected into one of the
large skeletal muscle –deltoid, triceps, gluteus or rectus
femoris .

18.  Absorption into the plasma occurs by simple diffusion . Large
molecules enter through the lymphatic channels .As the
muscle are vascular ,absorption is rapid and quite uniform.
 Drugs are absorbed faster from the deltoid region than
gluteal region especially in women .The volume of injection
should not exceed 10ml .For infants rectus femoris is used
instead of gluteus which is not well-developed till the child
start walking .oily solution or suspension ,the absorption is
slow and steady . smaller volume (1-2ml) deltoid muscle is
used if large volumes gluteal muscles should be used .
 Soluble substances ,Mild irritant ,depot preparations ,
suspensions and colloids can be injected by this route.

19. ADVANTAGES :
 Intramuscular route is reliable.
 Absorption is rapid.
 DISADVANTAGES :
 IM injection may be painful.
 It may result in an abcess.
 Risk of nerve injury –irritant solutions can damage the
nerve if injected near the nerve.The needle may also be
puncture the blood vessel.

20. INTRAVENOUS (IV)
 Here ,the drug is injected into one of the superficial veins
so that it directly reaches the circulation and is
immediately available for action.
 Drug can be given IV as :
 1.A bolus: the drug is dissolved in a suitable amount of
vehicle and injected slowly.An initial large dose is
given,e.g .heparin.
 2.slowly : over 15-20 min,e.g.aminophylline.
 3.slow infusion: when constant plasma concentration are
required ,e.g.oxytocin in labor or when large volumes
have to be given,e.g.dextrose, saline.

21. ADVANTAGES :
 IV route is useful in emergencies because the drug is
immediately available for action.
 It gives 100% bioavailability.
 Large volume and irritants can be given,they quickly diluted in
blood.
 Rapid dose adjustments are possible-if unwanted effectes
occur,infusion can be stopped.
 DISADVANTAGES :
 Once injected ,the drug cannot be withdrawn.
 Irritation of the vein may cause thrombophlebitis.
 Self medication is difficult.
 The solution should be sterile and strict aseptic measures should
be taken.

22. Administration of IV solutions
 Maintain strict asepsis.
 Before starting infusion the IV line should be flushed with
saline.
 Watch for sign of extravasation of fluid and
thrombophlebitis.
 Make sure that there are no air bubbles in syringe and
tubing.
 Intraperitonial :
 Peritonium offers a large surface area for absorption .
 This route is also used for peritonial dialysis.

23.  Intrathecal :
 Drugs can be injected into the subarachnoid space for
action on the CNS,e.g .spinal anesthetics.some antibiotics
and corticosteroids are also injected by this route to
produce high local concentrations.
 Intra-articular:
 Drugs are injected directly into a joint for the treatment of
arthritis and other diseases of the joints.strict aseptic
precautions are required,e.g .hydrocortisone is injected
into the affected joint,in rheumatoid arthritis.

24.  Intra-arterial:
 Here the drug is injected directly into the arteries.it is
used only in the treatment of peripheral vascular
disease, local malignancies and angiograms.
 Intramedullary:
 This route involves injection into a bone marrow –now
this rarely used.

25.  Inhalation :
 Volatile liquids and gases are given by inhalation,e.g
GA.Solution of drug particles and the fine droplets are
inhaled as aerosol, e.g . Salbutamol.Inhaled drugs and vapour
may act and absorbed on the pulmonary epithlium and
mucous membranes of the respiratory tract.
 ADVANTAGES :
 Almost instaneous absorption of the drug is achieved because
large surface area of the lungs.
 Hepatic first pass metabolim is avoided.
 Absorption and excretion through lunges.
 DISADVANTAGES :
 Irritant gases may enhance pulmonary secretions and should
be avioded by this route.

26.  TRANSDERMAL ROUTE:
 Highly lipid soluble drugs can be applied over the skin for
slow and prolonged absorption ,e.g nitroglycerin ointment
in angina pectoris . Adhesive units, inunction,
iontophoresis and jet injection are some forms of
transdermal drug delivery.
 Adhesive units :
 Adhesive patches of different sizes and shapes made to
suit the area of application .site of the application are
chest, abdomen , upperarm ,back or mastoid region,e.g
hyosine, nitroglycerin fentanyl,estrogen,testosterone
transdermal patches.

27.  ADVANTAGES :
 Duration of action is prolonged.
 Provide constant plasma levels.
 Patient compliance is good.
 Inunction :
 In this route of administration the drug is rubbed in to the
skin and it gets absorbed to produce systemic effects.
 Iontophoresis :
 In this procedure ,galvanic current is used for bringing
about penetration of lipid insoluble drugs into the deeper
tissues where its action is required,e.g .salicylates, fluoride
iontophoresis is used in the treatment of dental
hypersensitivity.

28.  Jet injection :
 As absorption of drug occurs across the layers of the
skin ,
 TRANSMUCOSAL:
 Druga are absorbed across the mucous membranes. It
includes sublingual,nasal and rectal routes.
 Sublingual :
 Here, the tablet or pellet containing the drug is placed
under the tongue.it dissolved and the drug is absorbed
across the sublingual mucosa,e.g. Nitroglycerin,
nifedipine,buprenorphine.

29.  ADVANTAGES :
 Absorption is rapid –within minutes the drug reaches the
circulation.
 First pass metabolism is avoided.
 After the desired effect is obtained ,the drug can be spat out to
avoid the unwanted effects.
 DISADVANTAGES :
 Buccal ulceration can occur.
 Nasal :
 Drugs can be administered through nasal route .e.g. Oxytocin
spray ,oxymetazoline, budesonide for allergic rhinitis.
 Rectal :
 Rectum has a rich blood supply and drugs can cross the rectal
mucosa to be absorbed for systemic effect.

30.  Drugs absorbed from the upper part of the rectum are carried
by the superior hemorrhoidal vein to the portal circulation.e.g
indomethacin, chlorpromacine, diazepam can be given rectally.
 ADVANTAGES :
 Gastric irritation is avoided.
 Can be administered by unskilled persons.
 Useful in geriatric patient and others with vomiting and those
unable to swallow.
 DISADVANTAGES :
 Irritation of the rectum can occur.
 Absorption may be irregular and unpredictable.(enema )


31.  Enema is the administration of a drug in liquid form
into the rectum.enema may be evacuant or retension
enema.
 Evacuant enema: In order to empty the bowel,about
600ml of soap water is administered per rectum.it is
given prior to surgeries ,obstetric proceduresand
radiological examination of gut.
 Retention enema: The drug is administered with
about 100ml of fluids and is retained in the rectum for
local action.e.g prednisolone enema in ulcerative
colitis.

32.  TOPICAL:
 Drugs may be applied on the skin for local action as ointment
,cream , gel ,powder, paste,etc,drugs may also be applied on
the mucous membrane ascin the eyes ,ears , and nose as
ointment ,drops and sprays.
 Drugs may be administered as suppository for rectum ,bougie
for urethra and pessary (oval shape) and douche for
vagina.e.g antifungal pessaries in vaginal candidiasis.

33.  SPECIAL DRUG DELIVERY SYSTEM:
 In order to improve drug delivery ,to prolong the duration
of action and improve the patient compliance ,special drug
delivery system are used.some such systems are ocusert,
progestasert, transdermal adhesive unit , prodrug ,osmotic
pumps,computerized pumps and methods using
monoclonal antibodies and liposomes as carriers.
 Ocusert :
 Ocusert systems are thin elliptical units that contains the
drug reservoir which slowly release the drug by
diffusion.e.g pilocarpine ocusert used in glaucoma is
placed under the lid can deliver the pilocarpine for 7 days .

34.  Progestasert is inserted into the uterus where it delivers
progesterone constantly for one year.
 Trans dermal adhesive units:
 Prodrug is an inactive form of a drug which gets
metabolized to the active derivative in the body .e.g
dopamine does not cross BBB but levo dopa a prodrug
crosses BBB and it is converted to dopamine in the CNS .
Bacampicillin a prodrug of ampicillin.
 Osmotic pumps are small tablet shape units containing the
drug and an osmotic substances in two different
chambers.the tablet swallowed and reaches the gut ,water
enter into the tablet through SPM .the osmotic layers
swells and pushes thedrug slowly.

35.  Computerized miniature pumps: These are
Programed to release drugs at a definite rate and
continuously.e.g inslin and anticancer drugs.
 Monoclonal antibodies are antibodies against the
tumor .
 Liposome are phospholipids suspended in aqueous
vehicles to form minute vesicles .Drugs encapsulated
in liposomes .mainly used for malignant tumors.

36.  NURSES RESPONSIBILITIES :
 Ensure the correct drug is administered by theright
route and in the right dose.
 History of allergy should be taken particularly before
parentral administration of the drugs.
 Moniter the adverse effect.
 Drugs should be kept in safe place.
 Check the prescription ,drug label and the patients
name before the administration of drugs.

37. PHARMACOKINETICS

38. PHARMACOKINETICS
 Pharmacokinetics is the study of the absorption
,distribution , metabolism and excretion of the drugs,
i.e the movement of the drugs into ,within and out of
the body.
 once drug is administered it is absorbed ,i.e .enters the
blood,is distributed to different parts of the
body,reaches the site of action ,is metabolized and
excreted.
 All these processes involve passage of the drug
molecules across various barriers – like the intestinal
epithelium ,cellmembrane, renal filtering
membrane,capillary barrier.
 .


39.  Drugs may be transported across the membrane by
passive or active transport.
 Passive transport:
 The drug moves across a membrane without any need
for energy.

40. Active transport
 It is the transfer of drugs against a concentration of drugs
against a concentration gradient and needs energy.It is
carried by a specific carrier protein.
 only drugs related to natural metabolites are transported
by this process,
 e.g levodopa, iron , aminoacids, penicillin and probenecid
are given together ,the excretion of penicillin is delayed by
probenecid.

41. ABSORPTION Absorption is defined as the passage of the drug from the site of
administration into the circulation.for a drug to reach its site of
action,it must pass through various membranes depending on the
route of administration .
 Absorption occurs by one of the processes i.e .passive diffusion or
active transport.Thus except for IV route, absorption is important
for all other route of administration .
 several factor influence the rate and extent of absorption of a
drug.they are:
 1.Disintegration and dissolution time :The drug taken orally
should break-up into individual particles to be absorped.then it has
to dissolve in the GI fluids.In case of drugs given SC or IM ,the
drug molecules have to dissolve in the tissue fluids.liquids are
absorped faster than solids.

42.  Delay in disintegration and dissolution result in delayed
absorption.
 2.formulation :Inert substance used with drugs as
diluents like starch and lactose may sometimes interfere
with absorption.
 3.Particle size: small particle size is important for better
absorption of drugs.Drugs like corticosteroids ,griseofulvin
,digoxin ,asprin and tolbutamide are well absorped when
given as small particles.
 4.Lipid solubility: lipid soluble drugs are absorbed faster
and better by dissolving in the phospholipids of the cell
membrane.

43.  5.pHand ionization :Ionized drugs are poorly absorbed
while unionized drugs are lipid soluble and are well
absorbed.
 Acidic drugs remain unionized in acidic medium of the
stomach and are rapidly absorbed,e.g aspirin,barbiturates.
 Basic drugs are unionized when they are reach the alkaline
medium of intestine from where they are rapidly
absorbed,e.g pethidine,ephedrine.
 strong acid and bases are highly ionized and therefore
poorly absorbed ,e.g heparin, streptomycin.

44.  6.Area and vascularity of the absorbing surface:larger
area of the absorbing surface and more the vascularity –
better is the absorption.Thus most of the drug absorbed
from the small intestine.
 7.Gastrointestinal motility: Gastric emptying time-if
gastric emptying is faster ,the passage of the drug to the
intestines is quicker and hence absorption is faster.
 Intestinal motility – when motility is highly ed as in
diarrhea,drug absorption is reduced.

45.  8. Presence of food : Drugs may form complexes with
food,such complexes are poorly absorbed.e.g. Tetracycline
chelate Ca present food ,so absorption ed.
 9.Metabolism : Some drugs may be degraded in
gut,e.g.nitroglycerin,insulin.
 10.Diseases: The disease of the gut like malabsorption
and achlorhydria result in reduced absorption of drugs.

46. First pass metabolism
 First pass metabolism is the metabolism of the drug during its
passage from the site of absorption to the systemic
circulation.it is also called presystemic metabolism or first pass
effect.
 Drugs given orally may be metabolized in the gut wall and in
the liver before reaching the systemic circulation.the extent of
FPM differs from drug to drug and person to person.
 FPM may result in partial to total inactivation of the drug.when
it is partial , it can be compensated by giving higher dose of
particular drug,e.g nitroglycerin,salbutamol.

47.  Bioavailability is the fraction of the drug that reaches
the systemic circulation following administration of
any route. IV -100% Bioavailability ,chlortetracycline
30%,chloroquin 80% ,diazepam 100%.
 Bioeqivalence :it is the study of comparison
bioavailability of different formulation of the same
drug.

48. Distribution
 After a drug reaches the systemic circulation ,it gets
distributed to various tissues . it should be cross several
barrieers before reaching the site of action.
 like absorption distribution also involves the same
process,i.e filtration,diffusion ,and specialized transport.
 Various factors determine the rate and extent of
distribution, they are lipid solubility,ionization,blood flow
and binding to plasma proteins and cellular protein.
 unionized and lipid soluble drugs are widely distributed
through out the body.

49. 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 -acid glycoprotein.The free or unbound fraction of the drug
is the only form available for action,metabolism and excretion,
 The protein bound form serves as areservoir . PB prolongs the
duration and action of drug.e.g warfarin 99%,morphine
35%,ethosuximide and lithium 0%.
 One drug may displaces another binding site and result in
displacement interaction,warfarin 99% PB indomethacin
reduces its binding to 95%.free warfarin level incresed it
produce toxicity.

50.  Tissue binding : some drugs get bound to certain tissue
constituent because of special affinity for them. TB delays
excretion and thus prolongs the duration of drug.
 Lipid soluble drug like thiopentone sodium are bound to
adipose tisssue,bone-tetracycline,retina-chlorquine,thyroid-
iodine.
 Blood brain barrier (BBB) :The endothelial cells of the
brain capillaries have tight junctions.moreover glial cells
envelope the capillaries and together these form the
BBB.Only lipid solublle and unionized drugs can cross
BBB.
 E.G . Penicillin readily penetrates BBB.
 Placental barrier: Lipid soluble ,unionized drugs readily
cross the placenta.

51. Metabolism
 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 of the drugs are largely unchanged in urine,e.g
frusemide,atenolol.mainly drugs are metabolized in liver
some are metabolized kidney,lungs,blood and skin.

52.  The chemical reactions of biotrasformation can take place
in two phases,
 1.phase I (Non-synthetic reactions) : 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 reaction) : in this reactions water
soluble substance present in the body like glucuronic
acid,sulfuric acid or an aminoacid combine with the drug
to form a highly polar compounds it excreted by the
kidneys.large molecules are excreted through the bile.

53. Excretion
 The major organs of excretion are the kidneys,intestine,biliary
systemand the lungs.Drugs are small amounts are excreted in
saliva,sweat ,and milk.
 Renal excretion
 Kidney is the most important organ of drug excretion.highly
lipid soluble drugs are reabsorbed in in the renal tubules ,so
their excretion is slow.
 Unabsorbed portion of the orally administered drugs are
eliminated through the feces.large water soluble conjugates are
excreted in the bile.
 The lungs are the main route of elimination for gases and
liquids, e.g. GA , Alcohol.

54.  Plasma half-life (t1/2) is the time taken for the plasma
concentration of a drug to be reduced to half its value.
 Minimum dose is the smallest dose required to produce a
desired therapeutic effect of the drug.
 Maximum dose is the largest dose of the drug that can be
safely given to a patient without producing harmful effect.
 Toxic dose is the dose of the drug which produce
undesirable effects in majority of the patients
 Lethal dose is the dose of the drug which can cause
death.e.g lethal dose of phenobarbitone is 6-10gm.

55. PHARMACODYNAMICS

56. PHARMACODYNAMICS
 Pharmacodynamics is the study of actions of the drugs on
the body and their mechanism of action, i.e to know what
drugs do and how they do it.
 Drugs produce their effects by interacting with the
physiological system of the organisms. By such
interaction drugs can only modify the rate of function of
various systems.
 e.g drugs may es or es the secretions.but they cannot
change the basic funtion of any physiological system.

57.  Thus drugs act by :
 1. stimulation
 2.Depression
 3.Irritation
 4.Replacement
 5.Anti-infective or cytotoxic action
 6.Modification of the immune status
 Stimulation is thees in activity of the specialized
cells, e.g adrenaline stimulates the heart.

58.  Depression is the es in activity of the specialized cells, e.g
quinidine depresses the heart.
 Irritation : This can occur on all types of tissues in the body and
may result in inflammation, corrosion and necrosis of cells.
 Replacement : drugs may be used for replacement when there
is deficiency of natural subatances like hormones ,metabolites
or nutrients ,e.g insulin in diabetes, iron in anemia ,vit C in
scurvy.
 Anti –infective and cytotoxic action: drugs may act by
specifically destroying infective organism,e.g penicillin
,cytotoxic effect on cancer cells.


59.  Modification of immune status:
 vaccines and sera act by improving our immunity
while immunosuppressants act by depressing
immunity,e.g glucocorticoids.
 Sites and mechanism of drug action
 Sites :drugs may produce their effects by locally or
systematically.
 Local : drugs may act at the site of application.e.g
antibiotics,antifungal agent.

60.  Drugs may act by one or more complex mechanism of
action. funtamental mechanism of drug action may be:
 Through receptor
 Through enzymes and pumps
 Through ion channel
 By physical action
 By chemical interaction
 By altering metabolic processes

61.  Through receptor
 Drugs may interact specific receptor in the body.
 Through enzymes and pumps
 Drugs may act by inhibition of various enzymes,thus altering
the enzyme –mediated reaction ,e.g . Allopurinal inhibits the
enzyme xanthine oxidase ; acetazolamide inhibit carbonic
anhydrase.
 Through ion channel
 Drugs may interfere with the movement of ions across specific
channels, e.g . Ca channel blocker , K channel blocker.

62.  Physical action
 The action of drug could result from its physical
properties. E.g .absorption –activated charcoal in
poisoning.
 Chemical interaction
 Drugs may act by chemical reaction.
 Antacids - Neutralize gastric acids
 Oxidising agents - kmno4 (germicidal)
 Alternating metabolic processes
 drugs like antimicrobial alter the metabolic pathway
in the micro organism resulting destruction of MO.e.g
sulfonamides interfere with bacterial folic acid
synthesis.

63.  Receptor
 A receptor is a site on the cell with which an agonist binds to
bring about a change. Receptor are proteins.they may be
present in the cytoplasm or on the nucleus.
 Funtions of receptors
 The receptor has to identify the compound, and when the
compound binds to the receptor ,it has convey the message
to bring about a response.
 Agonist :An agonist is a substance that binds to the receptor
and produce a response.
 Antagonist :An antagonist is a substance that binds to the
receptor and prevents the action of agonist on the receptor.
 Partial agonist :It binds to the receptor but has low
intrinsic activity that is , produce partial response.

64. Drug synergism and antagonism
 When two or more drugs are given concurrently ,the effect may
be additive, synergistic or antagonistic.
 Additive effect : the effect of two or more drugs get added up
and the total effect is equal to the sum of their individual
actions.e.g . Ephedrine with theophylline in bronchial asthma.
 Synergism : when action of one drug is enhanced or facilitated
by another drug the combination is synergistic.here the total
effect of the combonation is greater than the sum of their
independent effect.it is often called ‘potentiation’ or supra-
additive effect.e.g acetylcholine + physostigmine.

65.  Antagonism : one drug opposing or inhibiting the
action of another drug is antagonism.based on the
mechanism antagonism may be
 Chemical antagonism ,
 physiological antagonism ,
 Antagonism at the receptor level
 -Reversible (competitive)
 -Irreversible
 Non- competitive antagonism

66.  Chemical antagonism: Two subtaces chemically interact
to result in inactivation of the effect,e.g . Antacid like
aluminium hydroxide netralize gastric acids.
 Physiological antagonism : Two drugs act at different
sites to produce opposing effect. E.g . Insulin and
glucogan have opposite effects on the blood sugar level.
 Antagonism at the receptor level
 The antagonist inhibits the binding of the agonist to the
receptor .such antagonism may be reversible or
irreversible.

67.  Reversible competitive antagonism : The agonist and
antagonist compete for the same receptor . By incresing the
concentration of the agonist,the antagonism can be overcome.it is
thus reversible antagonism.Ach and atropine compete at
muscarnic receptor .the antagonism can be overcome by
incresing the concentration of Ach at the receptor.
 Irreversible antagonism : The antagonist binds so firmly by
covalent bonds to the receptor that it dissociate slowly not at
all.it block the agonist the blockade cannot be overcome by
increase the dose of agonist hence it is irreversible
antagonism,e.g. Adrenaline and phenoxybenzamine at -
adrenergic receptor.

68. Factors modifying the drug action
 Various factor modifying the drug action.they are
 1.body weight : The recommented dose is calculated for
medium and built persons.for the obese and underweight
persons,the dose has to be calculated individually.
 Dose = body wt (kg)/70 x average adult dose

 2. Age : In the new born ,the liver and kidney are not fully
mature to handle the drugs,e.g barbiturates which produce
sedation in adults may produce excitation in children.
 Youngs formula, childs dose = age (years) x adult dose
 age +12

69.  3.Sex : The hormonal effects and smaller body size
may influence drug response in women.special care is
necessary while prescribing for pregnant and lactating
women during menstruation.
 4.species and race : response to drug may vary with
species and race.e.g. Rabbits are resistant to atropine
need more dose to produce mydriasis.
 5.Diet and environment : food interfere with the
absorption of the drugs. e.g.tetracycline form
complexes with Ca present in the food and are poorly
absorbed.

70.  6.Route of administration : route of administration may
modify the pharmacodynamic response.e.g. Mgso4 given
orally it is a purgative,in IV it causes CNS depression and
has anticonvulsion effects.applied topically it reduce local
edema.
 7.Genetic factor : the enzyme production are genetically
controlled. The responce of the drugs differ according to
the metabolizing enzymes.
 A. Acetylation of drugs : the rate of drug acetylation
differs among individuals people may be fast or slow
acetylators.e.g. INH,sulfonamides and hydralazine.

71. B.G6PD deficiency : primaquine,sulphones and quinolones
can cause hemolysis in such people.
8.Dose : it is interesting to know the response of the drug,
the dose is increased the response also increased till the
maximum reached .incase some drugs further increased
the drug response is lowered.e.g. Myasthenia gravis
,neostigmine enhance the muscle power in therapeutic
doses in higher the dose it produce muscle paralysis.
9.Diseases : presence of certain disease can influence drug
responses,e.g . Malabsorption –drugs are poorly absorbed
,liver diseases-rate of metabolism reduced.

72.  10.Repeated dosing :Can result in
cumulation,tolerance,tachyphylaxis.
 Cumulation : Drugs like digoxin which are slowly eliminated
may cumulate resulting in toxicity.
 Tolerance :Tolerance is defined as the capacity of the body to
become less responsive to a substance.
 Lethal dose of Morphine is 250 mg, addict can tolerate
morphine in gm.

73.  Trachy phylaxis : is the rapid development of tolerance.when
some drugs are administered repeadly at short interval
,tolerance develops rapidly and is known as tachyphylaxis or
acute tolerance.
 11.Psychological factor : the docter patient relationship as
well as the nursing care influence the response to a large extent
by acting on the patient psychology .The patients confidence in
the doctor may itself be sufficient to relieve a suffering
,particularly the psychomatic disorder.placebo is the inert
dosage form with no biological activity but only resembles the
actual preparation in appearance.

74.  12.presence of other drugs :
 The concurrent use of two or more drugs can
influence the response of each other.