Posology in Pharmacology: Factors Affecting Drug Dosage
Mr.
Lakshmana Rao P
M.A.M
College
of
Pharmacy,
K
esanupalli, NRT
Posology: (Derived
from
the
greek
words
Posos-
how much,
and
logos
means
science).
Posology
is
a
branch
of
medical
science
which
deals
with
dose
or
quantity
of
drugs
which
can
be
administered
to
a
patient
to
get
the
desired
pharmacological
action.
The
dose
of
a
drug
cannot
be
fixed
rigidly
bec.
Various
factors
are
responsible
i.e
age,
sex,
severity
of
the
disease
etc.
The
official
doses
in
pharmacopoeia
represent
the
average
range
of
quty.
Suitable
for
adults
which
is
administered
orally
within
24
hrs.
When
other
routes
of
administration
are
followed
the
relevant
appropriate
dose
is
given.
1.Age
2.Sex
3.
Body
weight
3.
Route
of
administration
5.Time
of
administration
6.Enviourmental
factor
7.Emotinal
factor
8.Presence
of
disease
9.Accumulation
10.Additive
effect
11.Synergism
12.Antagonism
13.Idiosyncrasy
14.Tolerance
15.Tachyphylaxis
16.Metabolic
disturbance
A
g
e
:
-
The
pharmacokinetics
of
many
drugs
changes
with
age.
-
Newborn
infants
(pediatric)
are
abnormally
sensitive
to
certain
drugs
because
of
the
immature
state
of
their
hepatic
and
renal
function
by
which
drugs
are
inactivated and
eliminated
from
the
body.
Failure
to
detoxify
and
eliminate
drugs
results
in
their
accumulation
in
the
tissues
to
a
toxic
level.
-
Whereas,
elderly
patients
are
more
sensitive
to
some
drug
effect
e.g.
hypnotics which
may
produce
confusion
state
in
them.
S
e
x
:
-
Women
do
not
always
respond
to
the
action
of
drug
in
the
same
manner
as
it
done
in
men.
-
Special
care
should
be
taken
when
drugs
are
administered
during
menstruation,
pregnancy
&
lactation.
-
The
strong
purgative
eg.
Aloes
should
be
avoided
during
menstruation.
-
Similarly
the
drugs
which
may
stimulate
the
uterine
smooth
muscles
e.g.
drastic
purgative,
antimalarial
drugs,
ergot
alkaloids
are
contra
indicated
during
pregnancy.
-
Alcohol,
barbiturate,
narcotic
drugs
acts
on
foetus
through
placenta.
-
During
lactation,
morphine,
tetracycline avoided
because
its
affect
on
babies.
B
o
d
y
w
e
i
g
h
t
:
-
The
average
dose
is
mentioned
either
in
terms
of
mg
per
kg
body
weight.
-
Another
technique
used
as
a
total
single
for
an
adult
weighing
between
50-100kg.
-
However,
the
dose
expressed
in
this
fashion
may
not
apply
in
case
of
obese
patients,
children
&
malnourished
patients.
It
should
be
calculated
according
to
body
weight.
R
o
u
t
e
o
f
a
d
m
i
n
i
s
t
r
a
t
i
o
n
:
-
I
.
V
dos
e
s
o
f
d
r
ug
ar
e
usual
l
y
s
m
alle
r
th
a
n
the
oral
doses,
bec…
-
Intrav
e
n
ou
s
rout
e
thi
s
might
en
h
anc
e
the
chances
of
drug
toxicity.
-
Th
e
ef
f
ec
t
iv
e
ness
of
generally
controlled
administration.
dru
g
fo
r
mulation
is
b
y
th
e
ro
u
t
e
of
T
i
m
e
o
f
a
d
m
i
n
i
s
t
r
a
t
i
o
n
:
-
The
presence
of
food
in
the
stomach
delay
the
absorption
of
drug
&
rapidly
absorbed
from
the
empty
stomach.
-
But
it
does
not
mean
that
much
effective
when
taken
during
or
after
meal.
-
Iron,
arsenic &
cod-liver
oil
should
be
given
after
meal
&
antacid
drugs
taken
before
meal.
E
n
v
i
r
o
n
m
e
n
t
a
l
f
a
c
t
o
r
s
:
-
The
personality
&
behavior
of
a
physician
may
influence
the
effect
of
drug
especially
the
drugs
which
are
intended
for
use
in
a
psychosomatic
disorders.
-
The
females
are
more
emotional than
male
&
required
less
dose
of
certain
drugs.
-
Inert
dosage
forms
called placebos
which
resemble
the
actual
medicament
in
the
physical
properties
are
known
to
produce
therapeutic
benefit
in
disease
like
angina
pectoris
&
bronchial
asthma.
P
r
e
s
e
n
c
e
o
f
d
i
s
e
a
s
e
:
-
Drugs
like
barbiturates
&
chlorpromazine
may
produce
unusually
prolonged
effect
in
patient
having
liver
cirrhosis.
-
Such
as,
streptomycin
produce
toxic
effect
on
these
patient
their
kidney
function
is
not
working
properly
because
streptomycin
excreted
through
kidney.
A
c
c
u
m
u
l
a
t
i
o
n
:
-
Some
drugs
produces
the
toxic
effect
if
it
is
repeatedly
administered
for
long
time
e.g.
digitalis,
emetine,
heavy
metals
because
these
drugs
excreted
slowly.
-
This
occurs
due
to
accumulative
effect
of
the
drug.
A
d
d
i
t
i
v
e
e
f
f
e
c
t
:
-
When
two
or
more drugs
administered
together
is
equivalent
to
sum
of
their
individual
pharmacological
action,
the phenomenon
is
called
as
additive
effect.
-
E.g
ephedrine
&
aminophylline
in
the
treatment
of
bronchial
ashtma.
S
y
n
e
r
g
i
s
m
:
-
When
desired
therapeutic
result
needed
is
difficult
to
achieve
with
single
drug
at
that
time
two
or
more
drugs
are
used
in
the
combination
form
for
increasing
their
action
this
phenomenon
is
called
synergism.
-
E.g.
procaine
&
adrenaline
combination,
increase
the
duration
of
action
of
procaine.
A
n
t
a
g
o
n
i
s
m
:
-
When
the
action
of
one
drug
is
opposed by
the
other
drug
on
the
same
physiological
system
is
known
as
drug
antagonism.
-
The
use
of
antagonistic
response
to
drugs
is
valuable
in
the
treatment
of
poisoning.
-
E.g.
milk
of
magnesia is
given
in
acid
poisoning
where
alkaline
effect
of
milk
of
magnesia
neutralise
the
effect
of
acid
poisoning.
-
When
adrenaline
&
acetylcholine
are
given
together,
they
neutralise
the
effect
of
each
other
due
to
antagonism
because
adrenaline
is
vasoconstrictor
&
acetylcholine
is
vasodilator.
I
d
i
o
s
y
n
c
r
a
s
y
:
-
Idiosyncrasy
is
also
called
as
allergy.
-
An
extraordinary
response
to
a
drug
which
is
different
from
its
characteristic
pharmacological
action
is
called
idiosyncrasy.
-
E.g.
small
quty.
of
aspirin
may
cause
gastric
hemorrhage.
-
E.g
some
persons
are
sensitive
to
penicillin
&
sulphonamide
because
they
produce
severe
toxic
effect.
T
o
l
e
r
a
n
c
e
:
-
When
an
unusually
large
dose
of
a
drug
is
required
to
elicit
an
affect
ordinarily
produced
by
the
normal
therapeutic
dose
of
the
drug,
the
phenomenon
is
called
as
drug
tolerance.
-
E.g.
smokers
can
tolerate
nicotine,
alcoholic
can
tolerate
large
quantity
of
alcohol.
-
The
drug
tolerance
is
of
two
types:
-
True tolerance,
which
is
produced
by
oral
&
parenteral
administration
of
the
drug.
-
Pseudo
tolerance,
which
is
produced
only
to
the
oral
route
of
administration.
T
a
c
h
y
p
h
y
l
a
x
i
s
:
-
When
some
drugs
administered
repeatedly
at
short
intervals,
the
cell
receptors
get
blocked
up
&
pharmacological
response
to
that
drug
decreased.
-
The
decreased
response
cannot
be
reversed
by
increasing
the
dose
this
phenomenon
is
called
tachyphylaxis
or
acute
tolerance.
-
E.g.
ephedrine
given
repeated
dose
at
short
intervals
in
the
treatment
of
bronchial
asthma
may
produce
very
less
response
due
to
tachyphylaxis.
M
e
t
a
b
o
l
i
c
d
i
s
t
u
r
b
a
n
c
e
:
-
Changes
in
water
electrolyte
balance
&
acid
base
balance,
body
temperature
&
other
physiological
factor
may
modify
the
effect
of
drug.
-
E.g.
salicylates
reduce
body
temperature
in
only
in
case
an
individual
has
rise
in
body
temperature.
They
have
no
antipyretic
effect
if
the
body
temperature
is
normal.
given
i
n
the
The
dose
of
a
drug
p
h
armacopoei
a
repr
e
sents
the
average
max.quty
of
drugs
which
can
be
administered
to
an
adult
orally
within
24
hrs.
The
doses
are
also
calculated
in
proportionate
to
age,
body
weight
&
surface
area
of
the
patient.
D
o
s
e
p
r
o
p
o
r
t
i
o
n
a
t
e
t
o
a
g
e
:
T
h
e
r
e
a
r
e
n
u
m
b
e
r
o
f
m
e
t
h
o
d
s
b
y
w
h
i
c
h
t
h
e
d
o
s
e
f
o
r
a
c
h
i
l
d
c
a
n
b
e
c
a
l
c
u
l
a
t
e
d
f
r
o
m
t
h
e
a
d
u
l
t
d
o
s
e
1.
Young’s
formula
2.
Dilling’s
Formula
3.
Fried’s
formula
4.
Cowling’s
formula
1
.
Y
o
u
n
g
'
s
f
o
r
m
u
l
a
:
T
h
i
s
f
o
r
m
u
l
a
u
s
e
d
f
o
r
c
a
l
c
u
l
a
t
i
n
g
t
h
e
d
o
s
e
f
o
r
c
h
i
l
d
r
e
n
'
s
u
n
d
e
r
1
2
y
e
a
r
s
o
f
a
g
e
.
A
g
e
i
n
y
e
a
r
s
D
o
s
e
f
o
r
t
h
e
c
h
i
l
d
=
-
-
-
-
-
-
-
-
-
-
-
-
-
X
A
d
u
l
t
d
o
s
e
A
g
e
i
n
y
e
a
r
s
+
1
2
2
.
D
i
l
l
i
n
g
’
s
f
o
r
m
u
l
a
:
T
h
i
s
f
o
r
m
u
l
a
i
s
u
s
e
d
f
o
r
calculating
the
doses
for
children
in
between
4
to
20
years.
This
formula
is
considered
better
because
it
is
easier
&
quick
to
calculate
the
dose.
A
g
e
i
n
y
e
a
r
s
D
o
s
e
f
o
r
t
h
e
c
h
i
l
d
=
-
-
-
-
-
-
-
-
-
-
-
-
-
-
x
A
d
u
l
t
d
o
s
e
2
0
3
.
F
r
i
e
d
’
s
F
o
r
m
u
l
a
:
T
h
i
s
f
o
r
m
u
l
a
i
s
u
s
e
d
f
o
r
c
a
l
c
u
l
a
t
i
n
g
of
dose
for
infants
up
to
2
years.
A
g
e
i
n
m
o
n
t
h
s
D
o
s
e
f
o
r
i
n
f
a
n
t
’
s
=
-
-
-
-
-
-
-
-
-
-
-
-
-
-
x
A
d
u
l
t
d
o
s
e
1
5
0
4
.
C
o
w
l
i
n
g
’
s
f
o
r
m
u
l
a
:
A
g
e
a
t
n
e
x
t
b
i
r
t
h
d
a
y
(
i
n
y
e
a
r
s
)
D
o
s
e
f
o
r
c
h
i
l
d
=
-
-
-
-
x
A
d
u
l
t
d
o
s
e
2
4
D
o
s
e
p
r
o
p
o
r
t
i
o
n
a
t
e
t
o
b
o
d
y
w
e
i
g
h
t
:
C
l
a
r
k
’
s
f
o
r
m
u
l
a
u
s
e
d
t
o
c
a
l
c
u
l
a
t
e
t
h
e
d
o
s
e
o
n
b
o
d
y
w
e
i
g
h
t
.
C
h
i
l
d
s
w
e
i
g
h
t
i
n
K
g
D
o
s
e
f
o
r
t
h
e
c
h
i
l
d
=
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
x
A
d
u
l
t
d
o
s
e
7
0
D
o
s
e
p
r
o
p
o
r
t
i
o
n
a
t
e
t
o
s
u
r
f
a
c
e
a
r
e
a
:
I
n
t
h
i
s
m
e
t
h
o
d
d
o
s
e
i
s
c
a
l
c
u
l
a
t
e
d
a
c
c
o
r
d
i
n
g
l
y
t
o
s
u
r
f
a
c
e
a
r
e
a
i
t
’
s
t
h
e
m
o
r
e
s
a
t
i
s
f
a
c
t
o
r
y
&
a
p
p
r
o
p
r
i
a
t
e
m
e
t
h
o
d
t
h
a
n
b
a
s
e
d
o
n
a
g
e
m
e
t
h
o
d
.
Surface area
of
child
Percentage
of
adult
dose=------------------
x
100
Surface area
of
adult
or
C
a
t
z
e
l
’
s
f
o
r
m
u
l
a
:
S
u
r
f
a
c
e
a
r
e
a
o
f
p
a
t
i
e
n
t
i
n
M
2
D
o
s
e
f
o
r
p
a
t
i
e
n
t
=
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
x
A
d
u
l
t
d
o
s
e
1
.
7
3
M
2
w
h
e
r
e
,
1
.
7
3
M
2
=
A
v
e
r
a
g
e
a
d
u
l
t
s
u
r
f
a
c
e
a
r
e
a
Posology, the science of determining drug dosage, is influenced by various factors including age, sex, body weight, route of administration, and more. Changes in pharmacokinetics with age, differing drug responses in men and women, and the importance of body weight in dosing are crucial considerations in administering drugs effectively. Awareness of these factors is essential for safe and efficient pharmacological action.
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Presentation Transcript
Mr. Lakshmana Rao P M.A.M College of Pharmacy, Kesanupalli, NRT
Posology: (Derived from the greek words Posos- how much, and logos means science). Posology is a branch of medical science which deals with dose or quantity of drugs which can be administered to a patient to get the desired pharmacological action. The dose of a drug cannot be fixed rigidly bec. Various factors are responsible i.e age, sex, severity of the disease etc. The official doses in pharmacopoeia represent the average range of quty. Suitable for adults which is administered orally within 24 hrs. When other routes of administration are followed the relevant appropriate dose is given.
1.Age 2.Sex 3. Body weight 3.Route of administration 5.Time of administration 6.Enviourmental factor 7.Emotinal factor 8.Presence of disease 9.Accumulation 10.Additive effect 11.Synergism 12.Antagonism 13.Idiosyncrasy 14.Tolerance 15.Tachyphylaxis 16.Metabolic disturbance
Age: - The pharmacokinetics of many drugs changes with age. - Newborn infants (pediatric) sensitive to certain drugs because of the immature state of their hepatic and renal function by which drugs are inactivated and eliminated from the body. Failure to detoxify results in their accumulation in the tissues to a toxic level. - Whereas, elderly patients are more sensitive to some drug effect e.g. produce confusion state in them. are abnormally and eliminate drugs hypnotics which may
Sex: - Women do not always respond to the action of drug in the same manner as it done in men. - Special care should be taken when drugs are administered during menstruation, pregnancy & lactation. - The strong purgative eg. Aloes should be avoided during menstruation. - Similarly the drugs which uterine smooth muscles e.g. antimalarial drugs, ergot indicated during pregnancy. - Alcohol, barbiturate, narcotic drugs acts on foetus through placenta. - During lactation, morphine, tetracycline avoided because its affect on babies. stimulate drastic purgative, alkaloids are may the contra
Body weight: - The average dose is mentioned either in terms of mg per kg body weight. - Another technique used as a total single for an adult weighing between 50-100kg. - However, the dose expressed in this fashion may not apply in case children & malnourished patients. It should be calculated according to body weight. of obese patients,
Route of administration: - I.V doses of drug are usually smaller than the oral doses, bec - Intravenous chances of drug toxicity. route this might enhance the - The generally administration. effectiveness controlled of drug by formulation the is of route
Time of administration: - The presence of food in the stomach delay the absorption of drug & rapidly absorbed from the empty stomach. - But it does not mean that much effective when taken during or after meal. - Iron, arsenic & cod-liver oil should be given after meal & antacid drugs taken before meal.
Environmental factors: - The personality & behavior of a physician may influence the effect of drug especially the drugs which are intended for use in a psychosomatic disorders. - The females are more emotional than male & required less dose of certain drugs. - Inert dosage forms resemble the actual medicament in the physical properties are known to benefit in disease like bronchial asthma. called placebos which produce therapeutic angina pectoris &
Presence of disease: - Drugs like barbiturates & chlorpromazine may produce unusually prolonged effect in patient having liver cirrhosis. - Such as, streptomycin produce toxic effect on these patient their kidney function is not working properly because streptomycin excreted through kidney.
Accumulation: - Some drugs produces the toxic effect if it is repeatedly administered digitalis, emetine, heavy metals because these drugs excreted slowly. for long time e.g. - This occurs due to accumulative effect of the drug.
Additive effect: - When two equivalent to sum of their individual pharmacological action, the phenomenon is called as additive effect. or more drugs administered together is - E.g ephedrine & aminophylline bronchial ashtma. in the treatment of Synergism: - When desired therapeutic result needed is difficult to achieve with single drug at that time two or more drugs are used in the combination form for increasing their action this phenomenon is called synergism. - E.g. procaine & adrenaline combination, increase the duration of action of procaine.
Antagonism: - When the action of one drug is opposed by the other drug on the same physiological system is known as drug antagonism. - The use valuable in the treatment of poisoning. of antagonistic response to drugs is - E.g. milk of magnesia is given in acid poisoning where alkaline effect of milk of magnesia neutralise the effect of acid poisoning. - When adrenaline & acetylcholine are given together, they neutralise the effect of each other due to antagonism because adrenaline is vasoconstrictor & acetylcholine is vasodilator.
Idiosyncrasy: - Idiosyncrasy is also called as allergy. - An extraordinary response to a drug which is different from its characteristic pharmacological action is called idiosyncrasy. - E.g. small quty. of aspirin may cause gastric hemorrhage. - E.g some persons are sensitive to penicillin & sulphonamide because toxic effect. they produce severe
Tolerance: - When an unusually large dose of a required to elicit an affect ordinarily produced by the normal therapeutic dose of the drug, the phenomenon is called as drug tolerance. - E.g. smokers can tolerate nicotine, alcoholic can tolerate large quantity of alcohol. - The drug tolerance is of two types: - True tolerance, which is produced by oral & parenteral administration of the drug. - Pseudo tolerance, which is produced only to the oral route of administration. drug is
Tachyphylaxis: - When some drugs administered repeatedly at short intervals, the cell receptors get blocked up & pharmacological response decreased. to that drug - The decreased response cannot be reversed by increasing the dose this phenomenon is called tachyphylaxis or acute tolerance. - E.g. ephedrine given repeated dose at short intervals in the treatment of bronchial asthma may produce very less tachyphylaxis. response due to
Metabolic disturbance: - Changes in water electrolyte balance & acid base balance, body physiological factor may modify the effect of drug. temperature & other - E.g. salicylates reduce body temperature in only in case an individual has rise in body temperature. They have no antipyretic effect if the body temperature is normal.
The pharmacopoeia max.quty of drugs which can be administered to an adult orally within 24 hrs. dose of a represents drug given the in average the The doses are also calculated in proportionate to age, body weight & surface area of the patient.
Dose proportionate to age: There are number of methods by which the dose calculated from the adult dose for a child can be Young s formula 1. 2. Dilling s Formula Fried s formula 4. Cowling s formula 3. Young's formula : This formula used for calculating the dose for children's under 12 years of age. Age in years Dose for the child = - - - - - - - - - - - - - X Adultdose Age in years + 12 1.
2. Dilling s calculating the doses for children in between 4 to 20 years. This formula is considered better because it is easier & quick to calculate the dose. Age in years Dose for the child = - - - - - - - - - - - - - - x Adult dose 20 3. Fried s Formula : This formula is used for calculating of dose for infants up to 2 years. Age in months Dose for infant s= - - - - - - - - - - - - - - x Adultdose 150 formula: This formula is used for
4. Cowlings formula: Age at next birthday (in years) Dose for child= - - - - x Adult dose 24 Dose proportionate formula used to calculate the dose on body weight. Childs weight in Kg Dose for the child = - - - - - - - - - - - - - - - - - - x Adult dose to body weight: Clark s 70
Dose proportionate to surface area : In this method dose is calculated accordingly to surface area it s the more satisfactory & appropriate method than based on age method. Surface area of child Percentage of adult d o s e = - - - - - - - - - - - - - - - - - - x 100 Surface area of adult or Catzel s formula: Surface area of patient in M2 Dose for patient = - - - - - - - - - - - - - - - - - - - - - - - - x Adultdose 1.73 M2 where, 1.73 M 2 = Average adult surfacearea
