An understanding of pharmacokinetics and pharmacodynamics can allow for a rational approach to prescribing medications for critically ill children. Absorption, distribution, metabolism, elimination, and the response to medications are affected by age and disease state. Various medications are used in the care of critically ill children. Many medications are prescribed for children based on dosing guidance from adult studies, however. Care providers must be cautious of the high risk for drug interactions and adverse reactions in the intensive care setting.