Pathophysiology
Clinical meaning
Pediatric drug dosing differs fundamentally from adult dosing because children are not 'small adults' โ they have distinct pharmacokinetic profiles that change with developmental stage. Neonates have higher body water content (70-80% vs 60% in adults), lower plasma protein binding (less albumin), immature hepatic enzyme systems (CYP450 enzymes mature at different rates, with CYP3A7 dominant at birth transitioning to CYP3A4), and immature renal function (GFR reaches adult levels by age 1-2 years). These differences affect drug distribution, metabolism, and excretion, making weight-based (mg/kg) dosing essential. Critically, the calculated dose must never exceed the maximum adult dose regardless of the child's weight.