**Posology**

**Contents**hide

__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__

__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.

**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**

**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.

**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.

**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.

**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.

**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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