Unit 47 Calculating Pediatric Dosage Basic Principles of

Unit 47 Calculating Pediatric Dosage

Basic Principles of Calculating Pediatric Dosage • Correct medication dosages for infants and children are based on weight, height, body surface area (BSA), and age. • An accurate dose is usually a fraction of the amount of medication given to an adult. • It is extremely important to calculate dosages accurately: a minor error can be extremely serious, causing an overdose and even death.

Basic Principles of Calculating Pediatric Dosage • There are only two acceptable ways to determine pediatric dosage: – Calculating dosage based on kilograms or pounds of body weight. – Calculating dosage based on body surface area (BSA).

Calculation of Dosage Based on Body Weight • Most drug manufacturers and medication reference books such as the Physician’s Desk Reference (PDR) provide a recommended pediatric dosage based on kilograms (kg) of body weight.

Calculation of Dosage Based on Body Weight • The infant or child must be weighed. – Usually weight is recorded in pounds and ounces or pounds and fractions of pounds. – The pounds must first be converted to kilograms. • Dosage can be calculated based on the child’s weight in kilograms.

Calculation of Dosage Based on Body Surface Area (BSA) • The BSA method is considered to be one of the most accurate methods of calculating dosages because it relies on both the height and weight of the child. • A nomogram is used to determine the BSA.

Calculation of Dosage Based on Body Surface Area (BSA) • To determine the BSA, the height of the child in inches (in) or centimeters (cm) is located on the left column of the nomogram. • The weight of the child in kilograms (kg) or pounds (lb) is located on the right column. • A straight edge is used to connect the two points. • The point of intersection on the middle column provides the BSA in m 2 (meters squared).

Calculation of Dosage Based on Body Surface Area (BSA) • Many drug manufacturers now provide a recommended dose per m 2. • The formula used to calculate dosage when this information is available is:

Calculating Pediatric Dosage • Example: A physician orders methotrexate 25 mg IM for an 8 -year-old girl with cancer. The manufacturer’s recommended dose is 30 mg/m 2. If a nomogram shows the child’s BSA is 0. 9 m 2, is 25 mg IM a safe dose for this girl? – Use the formula: 1 X = 30 x 0. 9 X = 27 – The child’s dose is 27 mg; the ordered dose of 25 mg is safe for this child.

Practical Problem • A physician orders Vantin 50 mg po (by mouth) q 12 h (every 12 hours) for a child who weighs 22 pounds. The manufacturer recommends a dose of 5 mg/kg q 12 h. • Is 50 mg a safe dose for the infant?

Practical Problem • Convert the infant’s weight to kilograms, set up the formula and solve: 22 lbs = 10 kg 1 X = 50 50 mg q 12 is the correct dose. 50 mg q 12 is a safe dosage for this child.