Posology
Learning objectives
At the end of this
lecture, student will be able to:
• Explain posology, minimum dose and maximum dose
• Classify child dose calculation methods
• List formulae for child dose calculation based on age of
the child
• Recall formula for child dose calculation based on body weight
• Recall formula for child dose calculation based on body surface
area of the child
Posology
• Greek words “Posos” meaning “How much” and “Logos” meaning
“science”.
• It is a branch of medical science that deals with the dose
or quantity of drugs that needs to be administered to a patient to get the
desired pharmacological action.
Dose
• Dose is the quantitative amount of drug administered or taken
by a patient for the intended medicinal effect.
Minimum dose
• Necessary to produce desired therapeutic effect.
Maximum dose
• Largest quantity which can be given safely to an
individual without producing harmful effects.
Dosing
of drugs in infants and children require a thorough consideration of the
differences in Pharmacokinetics and Pharmacology of a specific drug in
different age groups
Pharmacokinetics
Absorption
Elimination
Metabolism
Distribution
Pharmacology
Pharmacology is the study of drugs and their action on the
body.
Different age groups
New born (Neonate): Birth – 1 month
Infant: 2 – 23
months
Young child: 2- 5 years
Older child: 6- 12 years
Adolescent: 13-18 years
Adult: 18+
years
Seniors: ≥60 years
(When a human child learns to walk, the term toddler is
used)
Pediatric Dose
Selection
Some of the formulas that are used to calculate child doses use
the following criteria.
• Age of the child.
• Body weight of the child.
• Body surface area of the child
Formulas based on Age
1) Young’s formula
2) Dilling’s formula
3) Cowling’s formula
4) Fried’s formula (for infants)
5) Bastedo’s formula
6) Augusberger’s formula
7) Brunton’s formula
8) Fried’s formula
9) Martinet’s formula
I.
Based on Age
a)
Young’s formula:
Child‘s dose =
Age in years X adult dose
Age in years
+12
This formula is suitable to calculate
the dose for a child below 12 years.
b)
Dilling’s formula:
Child dose = Age in years X
adult dose
20
This formula is suitable to calculate
the dose for a child between 12 to 20 years.
c)
Fried’s formula:
Child dose = Age in months
X adult dose
150
This formula is suitable to calculate
the dose for infants.
formula
Child dose = Age
(in years) +1 x Adult dose
24
(or)
Child dose = Age
at next birthday x Adult dose
24
e) Fried’s
formula (for infants)
Child dose = Age
(in months) x Adult dose
150
f) Augusberger’s
formula
Child dose = 4(Age at next birthday) +20 x
Adult dose
100
II. Depending of body weight:
a) Clark’s formula
Childs’s dose = Weight
in pounds X adult dose
150
(70 kg = 150 lbs is the average weight of an adult).
III.
Based on surface area:
a) Crawford
– Terry Rourke method
Child dose = Body surface area of a child (m2)
x Adult dose
1.73
m2
Child
dose = Body
surface area of child X Adult dose
Body surface area of an adult
1.73m2 is the average body surface area of an adult
Summary
• Dose is the
quantitative amount administered or taken by a patient for the intended
medicinal effect.
• Minimum dose is
necessary to produce desired therapeutic effect.
• Maximum dose is
the largest quantity which can be given safely to an individual without
producing harmful effects.
• Formulae based on
age –Young’s formula, Dilling’s formula, Cowling’s formula, Fried’s formula
(for infants), Bastedo’s formula, Augusberger’s formula, Brunton’s formula,
Fried’s formula, Martinet’s formula.
• Formula based on
Body weight of the child – Clark’s formula
• Formula based on
Body surface area of the child – Crawford – Terry Rourke method.