2. POSOLOGY
• Posology : - Derived from the Greek words
{ posos – how much, and
logos – Science } is the branch of
medicine/pharmacy dealing with doses.
“Posology is a branch of medical science which
deals
with dose quantity of drug which can be administered
to a patient to get the desirable pharmacological
action.”
Dose : It is the quantitative amount administered or
taken by a patient for the intended medicinal
3. FACTORS INFLUENCING DOSE
• Age
• Sex
• Body weight
•Route of administration
• Time of administration
• Environmental factor
• Emotional factor
• Presence of disease
• Accumulation
• Additive effect
• Synergism
• Antagonism
•Idiosyncrasy
• Tolerance
• Tachyphylaxis
• Metabolic disturbance
4. 1. AGE
A. Newborn infants
a) Sensitive to certain drugs because of the
immature state of their hepatic and renal functions.
b) Failure to detoxify and eliminate drugs results in
their accumulation in the tissues to a toxic level.
B. Elderly patients
a) The decline in renal and hepatic function may
slow drug clearance and increases the possibility of
drug accumulation in the body and subsequent
toxicity.
b) Elderly individuals may also respond abnormally
to the usual amount of a drug because of age-
related alterations in target tissues and organs
5. Various formula a/c to age
1.Young formula – Used for calculating dose of child
from
1-12 years of age.
Child dose = Age in years / Age +12 ×Adult dose
2. Cowling’s formula – For calculating doses for
children
two years of age or older.
Child dose = Age at next birthday / 24 ×Adult dose
6. 3. Dilling’s formula -- Used for calculating dose
of child from 12-20 years of age
Child dose = Age in years / 20 × Adult dose
4. Fried’s formula – For an infant upto 24 months of
age
Child dose = Age in months / 150 × Adult dose
7. 2. SEX
The response of various drug’s action in women
is not recorded in the same manner as of men.
Special care to women is given when drugs are
administered during menstruation, pregnancy
and lactation.
Alcohol, barbiturates, narcotic and non-narcotic
analgesics are capable of crossing the placenta
and affecting the fetus.
Morphine and barbiturates may produce more
excitement before sedation in women.
During lactation antihistamines like morphine
and tetracycline drugs are prohibited.
8. 3. BODY WEIGHT
The average dose is mentioned either in terms of mg
per kg body weight.
Another method used as a total single dose for an
adult weighing between 50-100 kg.
However, the dose expressed in this fashion may
not apply in cases of obese patients, children and
malnourished patients.
It should be calculated a/c to body weight.
CLARK’S FORMULA
Child’s dose = Weight in (lbs) / 150 × Adult dose
= Weight in (kg) / 70 × Adult dose
9. 4. ROUTE OF ADMINISTRATION
The effectiveness of drug formulation is generally
controlled by the route of administration.
IV dose is lesser than oral dose. Because, the
drugs administered directly into the systemic
circulation.
For immediate action and special case intravenous
drugs are given.
5. TIME OF ADMINISTRATION
The presence of food in stomach delays the
absorption of drugs, while drugs are rapidly
absorbed in empty stomach.
The irritating drugs are better tolerated if
administered after meals. E.g. – Iron tablets, cod
liver oil and arsenic should always be given after
10. 6. ENVIRONMENTAL FACTORS
Daylight is stimulant, enhancing the effect of
stimulating drugs and diminishing the effect of
hypnotics.
Darkness is sedatives, hypnotics are more effective
at night.
Alcohol are more tolerated in cold environments
than in summer.
7. EMOTIONAL FACTORS
The personality and behavior of a physician may
influence the effect of drug especially the drug which
are intended for use in psychosomatic disorder.
The females are more emotional than males and
requires less doses of certain drugs.
11. 8. PRESENCE OF DISEASE
Drugs like barbiturates and chlorpromazine may
produce unusually prolong effect in case of liver
cirrhosis patients.
Some drugs may prove toxic if the kidney of the
patients
is not working properly.
9. ACCUMULATION
Drugs excreted slowly may built up high
concentration in the body and produce toxic
symptoms if it is repeatedly administered for a long
time. E.g. –digitalis, emetine and heavy metals.
12. 10. ADDITIVE EFFECT
When pharmacological actions of two or more drugs
is equivalent to sum of their individual
pharmacological action, the phenomena is called as
additive effect.
11. SYNERGISM
When two or more drugs are used in the
combination their action is increased. This
phenomena is called synergism.
12.ANTAGONISM
When the action of one drug is opposed by other
drug on the same physiological actions is known
as antagonism.
The use of antagonistic responses to drugs is
valuable in the treatment of poisoning.
13. 13. IDIOSYNCRASY
This term is now replaced by ‘Allergy’.
An extraordinary response to a drug which is
different from its characteristics pharmacological
actions is called as Idiosyncrasy.
14. TOLERANCE
When an unusual large dose of a drug is
required to elicit an affect ordinarily produced by
the normal therapeutic dose of the drug the
phenomenon is termed as drug tolerance.
15. METABOLIC DISORDER
Changes in water electrolyte balance and acid
base balance, body temperature may modify the
effects of drug.
14. Calculation based on body surface area
Child dose = body surface area
of the child 1.73 sq.m.×
Adult
dose
