Neonatal pharmacodynamics--basic principles. II: Drug action and elimination.

The concepts of pharmacokinetics and pharmacodynamics are summarized for the clinician who cares for the neonatal patient. Six important pharmacologic principles are simplified and presented in a fashion that should facilitate recall. In this article, the final three concepts are presented: (1) the mechanisms by which drugs exert their actions, (2) the essentials of drug elimination through biotransformation (metabolism) by the liver, and (3) the essentials of drug elimination by the kidney. Also discussed are elimination half-life, clearance, and what happens when these elimination mechanisms are overwhelmed, due to either an excess of the drug or immaturity of the newborn.