PSYCHOPHARMACOLOGY
(Short Notes)
DEFINITIONS, ROUTES OF DRUG ADMINISTRATION
Pharmacology
Pharmacology is
the science of drugs. In a broad sense, It deals with interaction of
exogenously administered chemical molecules (drugs) with living system.
Pharmacokinetics
What the body
does to the drug
Drug
It is the single
active chemical entity present in a medicine that is used for diagnosis,
prevention, treatment and cure of the disease.
Clinical Pharmacology
It is the
scientific study of drugs in man. It include pharmacodynamic and
pharmacokinetic investigation in healthy volunteers and in patients, evaluation
of efficacy and safety of drugs and comparative trials with other forms of
treatment
Definition of drug (WHO)
drug is the
substance or product which is used or intended to be used to modify or to
explore physical system or pathological state for the benefit of recipient.
Pharmacy
It is the art
and science of compounding and dispending drugs or preparing suitable dosage
forms for administration of drugs to man or animals.
Chemical name
It describes the
substance chemically
Non Proprietary name
It is the name
accepted by a competent scientific body such as the United States Adopted Name.
Brand Name
It is the name
assigned by the manufactures and it his property or trade mark
Essential Drug concept
Those that
satisfy the priority healthcare needs of the population. They are selected with
due regard to public health relevance, evidence on efficacy and safety, and
comparative cost effectiveness.
Maximum toxic consideration
Dose more than
required have toxic effect on body.
Minimum inhibitory concentration
Dose does not
effect less than a certain level. Doctors should recommend medications between
maximum toxic consideration and minimum inhibitory concentration.
Abbreviations use for the frequency of
taking medicines per day
OD… once a day
BD…Twice a day
TiD…Thrice a day
QiD... four times a day
Routes of Drug administration
Oral (oral ingestion is the oldest and commonest
mode of drug administration. It is safer and more convenient, does not need
assistance.
Sublingual (the tablet or pellet
containing the drug is placed under the tongue.
Rectal (certain irritant and unpleasant
drugs can be put into rectum as suppositories or retention enema for systemic
effect.
Cataneous (highly lipid soluble drugs
can be applied over the skin for slow and prolonged absorption.
Inhalation (volatile liquids and gases
are given by inhalation for systemic action.
Nasal (the mucous membrane of the nose
can readily absorb many drugs.
Parenteral (administration by injection
which takes the drug directly into the tissue fluid or blood with out having to
cross the intestinal mucosa.
Subcutaneous (the drug is deposited tin
the loose subcutaneous tissue which is richly supplied by nerves but is less
vascular.
Intramuscular (the drug is injected in
one of the large skeletal muscles.
Intravenous (the drug is injected
through superficial veins. It infused
slowly over hours and directly reached to the blood stream.
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PHARMACOKINETICS
Pharmacokinetics
is the quantitative study of drug movement in through and out of the body. All
pharmacokinetic processes involve transport of the drug across biological
membranes. This process involves in four stages, which are given below
Absorption
Distribution
Metabolism
Exertion
Now
we will discuss all these stages one by one !
Absorption
Absorption is
the movement of drug from its site of administration into the circulation. The
rate and extent of absorption of a drug from a dosage form is called
bioavailability.
Plasma Protein binding
Some kind of
protein available in plasma. When drug after absorption attach with these
proteins, drug’s bioavailability decrease.
Distribution
Once a drug has
gained access to the blood stream, it gets distributed to other tissues that
initially had no drug or the site of action.
Metabolism
This is also
called biotransformation. It means chemical alteration (when drug break down
into parts) of the drug in the body.
Factors involving in metabolism
These are the
chemical reactions by which drug metabolize in the body. These are oxidation,
reduction, hydrolysis and cyclization. These
factors are given below.
Oxidation
This reaction
involves addition of oxygen or removal of hydrogen. Oxidation are the most
important drug metabolizing reactions.
Reduction
This reaction is
the converse of oxidation and involves cytochrome enzymes working in the
opposite direction.
Hydrolysis
This is cleavage
of drug molecule by taking up a molecule of water.
Cyclization
This is
formation of ring structure form from a straight chain compound.
Exertion
Excretion is the
passage out of systemically absorbed drug. Drugs and other metabolites are
excreted through Urine, Faeces, Exhaled air, Saliva and Sweat and milk.
(Important Terms under discussing this
chapter)
Loading dose
This is a single
or few quickly repeated doses given in the beginning to attain as.
Maintenance dose
This dose is one
that is to be repeated at specified intervals after the attainment of target
Plasma half life of drug
The plasma half
of drug is time taken for its plasma concentration to be reduced to half of its
original value. Half life use for determining the dose interval . CNS drug
shaving short half life.
PHARMACODYNAMICS
Pharmacodynamics
is the study of drug effects, and attempts to explain the complete action
effect sequence and the dose effect relationship.
Principles of Drug Action
Stimulation
It is selective
enhancement of the level of activity of specialized cells.
Depression
It is selective
diminution of activity of specialized cells i.e. barbiturates depress CNS.
Irritation
This cannotes a
nonselective, often noxious effect and is particularly applied to less
specialized cells. I.e. bitters increase salivary and gastric secretion.
Replacement
This refers to
the use of natural metabolites, hormones or their congeners in deficiency
states.
Cytotoxic action
Selective
cytotoxic action for invading parasites or cancer cells, attenuating them
without significantly affecting the host cells is utilized or cure.
Other terms
discussed in this chapter
Receptor
These are the
macromolecules or binding cites present on the surface or inside the surface.
Most of the drugs exert their effects both the beneficial and harmful while interacting
with receptors.
Agonist
It activates a
receptor to produce and effect similar to that of the physiological signal
molecule.
Inverse agonist
It activates a
receptor to produce an effect in the opposite direction to that of the well
recognized agonist.
Antagonist
It prevents the
action of an agonist on a receptor or the subsequent response, but does not
have any effect of its own.
Partial agonist
It activates a
receptor to produce sub maximal effect but antagonizes the action of a full
agonist.
Affinity
It is the
ability of the drug to combine with the receptor.
Combined effect of drugs
When two or more
drugs are given simultaneously or in quick succession, they may be either
indifferent to each other or exhibit synergism or antagonism.
Synergism (together work)
When the action
of one drug is facilitated or increased by the other, thy are said to be
synergistic. Here both drugs have action in the same direction. There are two
types of synergism. Which are given below
Additive
The effect of the
two drugs are in the same direction and simply add up 1+1=2
Supraadditive
The effect of
combination is greater than the
individual effects of the components. 1+1=4
Antagonism
When one drug
decreases or inhibits the action of another, they are said to be antagonistic. There
are two types of antagonism, are given below
Physical antagonism
Based on the
physical property of the drugs, i.e. charcoal adsorbs alkaloids and can prevent
their absorption.
Chemical antagonism
The two drugs
react chemically and form an inactive product.
Target for drug action
Receptors
We have already
discussed
Ion channels
It is the direct
procedure of the target of drug action.
A class of drug
that is calcium channel blocker will act with ion channels and block the channels,
so muscle contraction in the blood pressure will be reduced.
Enzymes
Any of numerous proteins or conjugated proteins produced by
living organisms and functioning as biochemical catalysts.
Factors modifying the drug action
Age
The dose of a drug for children is
often calculated from the adult dose.
Formulas for calculating the
children’s dose of drug
Young’s formula
Child dose = age/age+12* adult
dose
Dilling’s formula
Child dose = age/20*adult dose
Body size
It has been argued that body
surface area provides a more accurate basis for dose calculation
Individual dose= BW (kg)/70*average adult
weight
Sex
Female have
smaller body size and require doses that are on the lower side of the range.
Subjective effects of drugs may differ in females because for their mental make
up.
Species and race
There are many
examples of differences in responsiveness to drugs among different species.
Among human beings some racial differences have been observed i.e. blacks
requires higher and Mongols require lower concentrations of atropine .
similarly beta blockers are less effective as anti hypertensive in blacks.
Route of administration
Route of
administration governs the speed and intensity of drug response. for example
magnesium sulfate given orally causes purgation while administered
intravenously it produces CNS depression and hypotension.
Environmental factors
Environmental factors affect drug responses. i.e. anti
hypertensive show good results in winter as compare to summer.
Psychological factors
Efficacy of a
drug can be affected by patient’s beliefs, attitudes and expectations.
Pathological state
Not only drugs
modify disease processes, several diseases can influence drug disposition and
drug action.
Adverse drug reactions
Adverse drug
reactions also play role in effectiveness of drug.
Food
Food is also
play a vital role in effectiveness of drug. i.e. when you use antibiotics take
it before meal
ADVERSE DRUG EFFECTS
Adverse effects
Adverse effect
is any undesirable or unintended consequence of drug administration.
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Severity of adverse drug reactions
Minor
No therapy, antidote or prolongation of
hospitalization required
Moderate
Requires change
in drug therapy specific treatment or prolongs hospital stay by at least one
day.
Severe
Potentially life
threatening causes permanent damage or requires intensive medical treatment.
Lethal
Directly or
indirectly contributes to death of the patient.
Side effects
These are
unwanted but often unavoidable pharmacodynamic effects that occur at
therapeutic doses.
Secondary effects
These are
indirect consequences of a primary action fo the drug.
Toxic effects
These are the
result of excessive pharmacological action of the drug due to over dosage or
prolonged use.
Intolerance
It is the
converse of tolerance and indicates a low threshold of the individual to the
action of a drug.
Idiosyncrasy
It is
genetically determined abnormal reactivity to a chemical. Certain adverse
effects of some drugs are largely restricted to individuals with a particular
genotype.
Drug allergy
It is an
immunologic ally mediated reaction producing stereotype symptoms which are
unrelated to the pharmacodynamic profile of the drug and are largely
independent of dosage.
Drug dependence
Drug dependence
is a state in which use of drugs for personal satisfaction is accorded a higher
priority than other basic needs, often in the face of known risks to health.
Drug abuse
Refers to use of
drug by self medication in a manner and amount that deviates from the approved
medical and social patterns in a given culture at a given time.
Drug addiction
It is a pattern
of compulsive drug use characterized by overwhelming involvement with the use
of a drug.
Teratogenicity
It refers to
capacity of a drug to cause foetal abnormalities when administered to the
pregnant mother.
Drug induced diseases
These are also
called iatrogenic (physician induced) diseases. i.e. Parkinson by
phenothiazines .
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