Drug Dosage Based on Body Surface Area (BSA)
For certain drugs, particularly chemotherapy drugs and pediatric drugs, the drug dose is based on BSA rather than weight. BSA is derived from the weight and height of the patient and is expressed as square meters (m2). The average adult is considered to have a BSA of 1.73 m2. A useful equation for calculation of dose based on BSA is:
$$ Patient's \ Dose = { Patient's \ BSA \ (m^2) \over 1.73 \ m^2 } \times Drug \ dose \ (mg) $$
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Solved Problem: If the adult dose for a drug is 70 mg per day. What dose should be given to a child with a BSA of 0.33 m2? Approach: Using the above equation, calculate the required dose. $$ Patient's \ Dose = { 0.33 \ (m^2) \over 1.73 \ m^2 } \times 70 \ (mg) $$ Answer: 13.4 mg |
In the above problem, the BSA of the patient was provided, but what if a calculation requires you to first calculate the BSA of a patient and then calculate the drug dose? BSA of a patient can be estimated from their height and weight using either the Nomogram method or the Mosteller equation.