# Posology

Contents

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

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.

d) Cowling’s 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.

## FAQs

1. Is posology only relevant for prescription medications?
• No, posology is relevant for all medications, including over-the-counter drugs. It ensures safe and effective use.
2. How often should posology recommendations be reviewed?
• Posology recommendations should be reviewed regularly, especially when there are changes in health status or additional medications are prescribed.
3. Can posology be different for the same drug in different formulations?
• Yes, posology may vary based on the formulation of a drug. Tablets, capsules, and liquid forms may have different dosage recommendations.
4. Are there tools to help individuals adhere to posology guidelines?
• Yes, technology-driven tools like medication reminder apps and smart pill dispensers assist individuals in adhering to posology guidelines.
5. Why is posology essential for pediatric patients?
• Posology for pediatric patients considers their age and weight, ensuring that medications are administered in safe and effective doses.

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