Pharmacokinetic variability occurs due to differences in drug absorption, distribution, metabolism, and excretion between individuals. Several factors influence this variability including age, body weight, pregnancy, and disease states. Drug metabolism and excretion are often lower in newborns compared to adults due to immature organ systems and lower enzyme levels. Plasma protein binding is also lower in newborns which increases drug distribution. Renal function is reduced in newborns leading to slower drug clearance. These developmental differences can increase the risk of adverse drug reactions in newborns if dosages are not appropriately adjusted.