Dose represents the amount of a drug to be administered or taken by the patient for therapeutic effect.

The dose may be expressed as:

Single dose: The amount of drug is taken one time.

Divided dose: The amount of drug is taken two or more times in a day depending on the characteristics of the drug, types of diseases and severity of diseases.

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Total dose: The amount of drug is taken during the complete therapy.

Dose calculation varies with age, weight, sex, surface area, and disease condition etc. of the patient. Because of these variables the Pharmacopoeia prescribes the “average adult dose” or the “usual adult dose” for official drugs. Therefore the adult dose as mentioned in the Pharamcopoeia may also vary depending on the various factors to be considered by the prescriber, the physician.

For calculating the doses for children the following methods are used :

I. Methods based on age of child:

A. Young’s Formula: The formula is most useful for the calculating the doses for children under 12 years of age.

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If the usual adult dose of drug is 60 mg, what is the dose for

(a) a child of 6 years (b) a child of 8 years

According to Young’s Formula

(a) Dose of child = -x 60 = 20 mg

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(b) Dose of child =—- x 60 = 16 mg

(a) 20 mg (b) 16 mg

B. Dilling’s Formula: The formula is most useful for the calculating the doses for children in between 4 to 20 years of age.

If the adult dose of Allopurinol is 200 mg, what is the dose for (a) a child of 12 years (b) a child of 16 years

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According to Dilling’s Formula

(a) Dose for child

(b) Dose for child 200 = 160 mg Answer

(a) 120 mg (b) 160 mg

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C. Cowling’s Formula

The maximum daily dose of a drug is 120mg . How much of it should be given to a child of (a) 11 years (b) 15 years

Dose for the child = = 60 mg

Dose for the child = = 80 mg

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(b) 80 mg

D. Fried’s Formula: The formula is most useful for the calculating the doses for children under 2 years of age.

The adult dose of a drug is 50 mg. How much of it can be to (a) a 6 month old infant (b) a 24 months old infants

Dose for the child = 2.0 mg

Dose for the child = 8.0 mg

Answer

(a) 2.0 mg (b) 8.0 mg

E. Bastedo’s Formula:

The adult dose of a drug is 100 mg. How much of it can be given to a patient

of (a) 9 years (b) 12 years

According to Bastedo’s Formula

Answer

(a) 40 mg (b) 50 mg

II. Method based on weight of the child

The adult dose of nimesulide is 100 mg. How much of it can be administered to a child weighing (a) 12 lbs (b) 15 lbs

According to Clark’s Formula

Dose for the child = = 8 mg

Dose for the child = = 10 mg

III. Method based on body surface:

The body surface area is widely used in two types of patient groups

(i) Chemotherapy receiving cancer patient

(ii) Pediatric patients of all childhood except premature and full-term newborns

In general the adult body surface area of an adult is considered as 1.73 m2

A dispensing pharmacist must remember the doses of important drugs commonly prescribed so as to ensure accuracy in dispensing and avoiding any errors. The doses and uses of commonly prescribed drugs as per Indian Pharmacopoeia are given in the following Table for ready reference.