Pharmacokinetics is the study of how drugs move through the body or the study of the following four processes, which can easily be remembered using the acronym ADME:

• Absorption: The movement of a drug into the bloodstream
• Distribution: The movement of a medication into body tissues and fluids
• Metabolism: The transformation of a drug into chemicals used by the body
• Elimination: The movement of a medication out of the body

The pharmacokinetics of acetaminophen (Tylenol), as noted on the package insert, indicate that this medication is:

• Absorbed mainly in the small intestine
• Distributed throughout most body fluids, except fat
• Metabolized (converted to and/or combined with other chemicals) in the liver
• Eliminated in several hours through the urine

This example demonstrates that adequately functioning body systems are needed for movement of medications throughout the body. Because body system function varies throughout an individual's life, and the impact of medications is affected by the way in which a body system functions, medication dosing may need to be altered during those ages and stages of life when body system function is minimized.