NTA Level 4 • Semester 1 • PST04105

Calculations of Doses for Paediatrics and Geriatrics Based on

Pharmaceutical Calculations • Source Session/Topic 11

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Session 11: Calculations of Doses for Paediatrics and Geriatrics Based on

Age, Body Weight and Body Surface Area

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Calculating the dose for paediatric by using age of a child

• Calculating the dose for paediatric by using body weight of a child

• Calculating the dose for paediatric by using body surface area

• Calculating of doses for elderly (geriatric) patients

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing.

STEP 2: Calculation of Paediatric Dose by Using Age of a Child (30 minutes)

• When paediatric doses for a medication are not given, they can be

calculated from the adult dose, taking into account body-surface area,

body-weight or age.

• Usually children are divided into four age groups;

o Neonates: 1 to 28 days

o Infants: 4 weeks to one year

o Children: 1 to 5 years

o Children: 6 to 12 years

• The age of the individual being treated is frequently a consideration in

the determination of the drug dosage, especially in the young and very

old

• The rationale for dose adjustment in paediatric indications may be

determined by differences in pharmacokinetics, pharmacodynamics, disease

or a combination of these factors

• Pharmacokinetics of drugs in children may differ from adults for several

reasons such as:

o age

o gender

o body composition

o functionality of liver and kidneys

o maturation of enzymatic systems throughout the life span from

neonates to adults

• There are different formulas for determination of paedriatic (child) dose

based on age, these include:

o Young’s Rule; Age (in years)/(Age + 12) × Adult dose = Dose for

Child

o Fried’s Rule; (Age ( in months) × Adult dose)/150 = Dose for Child

|Activity: Small Group Discussion ( 15 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|Calculate the dose for 6-years old child when the adult dose is 600 mg |

|What is the dose of a medication for a twelve months old child when the|

|adult dose is 100 mg? |

| |

|ALLOW students to discuss for 10 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

The following is the answer for the above exercise:

• Child’s dose = 6/(6+12) × 600 =200 mg

The child’s dose is 200 mg Answer

• Child’s dose = (12 × 100)/150 = 8 mg

The child’s dose is 8 mg Answer

STEP 3: Calculation of Paediatric Dose by Using Body Weight of a Child (30

minutes)

• The usual doses for drugs are considered generally suitable for 70kg (154-

lb) individuals

• The determination of drug dosage for young patient on the bases of body

weight is considered more dependable than that based strictly on age

• The dosage of a number of drug substances is based on body weight and is

frequently expressed on a milligram (drug) per kilogram (body weight) or

milligram per pound bases

• Formulas for calculating child’s dose based on body weight include:

o Child’s dose = (child body weight (Kg) × Adult dose)/70 Kg

o Child’s dose = (child body weight (lb) × Adult dose)/150 lb

|Activity: Small Group Discussion ( 15 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|Calculate the dose for a child which weighs 17.5 Kg when the adult dose|

|is 0.5 g |

|If the adult dose of a drug is 75mg, what will be the dose for a child |

|weighing 40 lb? |

|ALLOW students to discuss for 10 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• The following are the answers of the above exercise

Child’s dose = (17.5Kg × 0.5 g)/70 Kg = 0.125 g

The child’s dose is 0.125g answer

Child’s dose = (40 lb × 75 mg)/150 lb = 20 mg

The child’s dose is 20 mg answer

STEP 4: Calculation of PaediatricDose by Using Body Surface Area and

Height ( 30 minutes)

• Dose calculated on bases of body surface area (BSA) or body weight is

much more satisfactory and always needed when the margin between

therapeutic and toxic dose is narrow

• For more precise calculation of doses based on BSA, one should refer

to a standard nomograph, which includes both weight and height as

factors influencing BSA

• Formulas to calculate child dose based o BSA include;

Child’s dose = (BSA of a child in m2 × Adult dose) / 1.73m2 (average

adult BSA)

|Activity: Small Group Discussion ( 15 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|What is the dose of a drug for a child having a BSA of 0.54m2 when the |

|adult dose is 50 mg? |

|ALLOW students to discuss for 10 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• The following are the answers of the above exercise.

Child’s dose = (0.54m2× 50 mg)/1.73m2 = 15.60 mg answer

STEP 5: Calculations of Doses for Elderly (Geriatric) Patients (10 minutes)

• Geriatric medicine or geriatrics is the field that encompasses the

management of illness disability in the elderly

• Most age related physiological functions peak before age 30 years with

subsequent gradual linear decline

• Kidney function is a major consideration in a drug dosing in the elderly

because reduced function results in reduced drug elimination, this will

lead to drug accumulation and prolongation in the body and possible drugs

toxic levels and related adverse events

• Renal clearance as well as other pharmacokinetic parameters, are

important in the dosing of certain drugs in the elderly patients

population

• Therefore dose reduction is important in elderly patients due to

reduction in their renal and hepatic functions

STEP 6: Key Points (5 minutes)

• Pediatric doses can be calculated from the adult dose, taking into

account body-surface area, body-weight or age

• Dose calculated on bases of body surface area (BSA) or body weight is

much more satisfactory and always needed when the margin between

therapeutic and toxic dose is narrow

• Renal clearance as well as other pharmacokinetic parameters

(malabsorption, metabolism by the liver) are important in the dosing of

certain drugs in the elderly patients population

STEP 7: Evaluation (5 minutes)

• What are different methods used in the determination of child dose?

• What are the reasons for calculating child dose?

• What are the two important factors to consider when determining doses for

elderly patients?

STEP 8: Assignment (5 minutes)

|Activity: Take home Assignment (5 minutes) |

| |

|ASK each individual student to do the following assignment |

| |

|What is the dose of 6 month old child when the adult dose is 250 mg of|

|a drug? |

|What is the dose of diclofenacinjection of a child weigh 14 kg while |

|the adult dose is 150 mg. |

|Calculate the dose of a 12 years old child while the adult dose of |

|drug is 1000 mg. |

|Calculate the dose of a child with BSA of 0.25 m2 when the adult dose |

|is 250 mg |

| |

|ALLOCATE time for students to do the assignment and submit |

| |

|REFER students to recommended references |

References

Ansel, H. C & Stocklosa, M. J. (2001). Pharmaceutical Calculations (11th

ed.). Philadelphia, United States: LIPPINCOTT WILLIAMS & WILKINS

Ansel, H. C (2010) Pharmaceutical Calculations (13rd ed.). Philadelphia,

United States: LIPPINCOTT WILLIAMS & WILKINS

Senya, S. S, Mwasha, C.Y, Muyinga, A. M, Amiri,R. I. and Mauga E.A.S.K.

(2011) Tanzania Pharmaceutical Handbook (2nd ed.). Dar eS Salaam,

Tanzania: School of Pharmaceutical Sciences.

Zatz, J.L and Teixeira, M.G. (2005). Pharmaceutical Calculation (4th ed.).

New Jersey: John Wiley & Sons, Inc

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