For pediatric dosing of acetaminophen, which parameter is most important to determine the dose?

• A. Eye color
• B. Age in years
• C. Height
• D. Weight in kilograms

Answer: (D)

Body weight in kilograms is the parameter that best guides pediatric acetaminophen dosing because how a drug distributes and is cleared from the body scales more reliably with body size than with age or height. Using milligrams per kilogram per dose ensures the amount given matches the child’s actual mass, so smaller children aren’t overdosed and larger children aren’t underdosed. Relying on age in years can be misleading since kids of the same age can have widely different weights and body compositions, making a single fixed dose too strong for some and too weak for others. Height alone isn’t a precise proxy for how much drug to give, because two children with the same height can have different weights. Eye color, of course, has no relevance to drug dosing.

For context, acetaminophen dosing is typically expressed as a dose in milligrams per kilogram, given at intervals of several hours as needed, with a daily maximum to protect against liver toxicity. Keeping the dose tied to weight is the safest and most consistent approach across the diverse pediatric population.