PHARMACOLOGY

 DOSAGE CALCULATIONS ::

Rules for Infants and children s doses :: 

1.Young s Rule (for children 2 years and above ):

        Age (yr) 

        ------------ * Adult dose = Child s dose (approx) 

        Age (yr)+12

2.   Clark s Rule ::

        Weight (Ib) 

        -------------- *Adult dose = Child s dose (approx) 

            150

3. Fried s Rule (for infants upto 2 years age ) 

        Age (months) 

        ----------------- * Adult dose = Infant s dose (approx) 

            150

Rules for calculating dosage on prescription orders :

1. To find the amount of an ingredient /dose in a compound prescription order divide the total amount of ingredients prescribed by the number of doses administered 

2.To find the total amount of an ingredient used in a compound prescription order multiply the amount /dose prescribed by the total number of doses 

3.The squaremeter surface area method relates to the surface are of the individual to dose 

    Body surface area of child 

    -------------------------------- *Adult dose = Child s dose (approx) 

    Body surface area of adult 

    The average body surface area for an adult has been given as 1.73 sq.meters :

    Body surface area of child (m2) 

    --------------------------------------- * Adult dose = Child s dose 

            1.73 m2 

many drugs have doses stated in mg /kg body weight and may be calculated  as follows :

    Amount of drug x body surface area (m2)= individual s dose 

4.Drug doses are often stated in mg /kg body weight and may be calculated as follows :;

mg/kg x body wt. (kg) = Individual s dose 

5. Drug doses may also be stated in units e.g. vitamins A and D antibiotics and hormones This means that a certain quantity of biologic activity of the drug is called 1 unit 

    These schedules are more of theoretical interest (with simple drugs ) in the hands of paediatric practice