Neonatal Pharmacology—Pharmacokinetics

As IN MOST ASPECTS OF neonatology, clinical pharmacology in the newborn is uniquely dependent upon age-related maturation, which is responsible for alterations in pharmacokinetics (drug disposition, or what the body does to the drug) (See Glossary), and pharmacodynamics (what the drug does to the body) when compared to the adult. Drug disposition involves the action of drugs in the body over a period of time, including the pharmacokinetic processes of absorption, distribution, localization in tissues, metabolic biotransformation, and excretion. How maturational differences affect these processes is especially apparent in newborns and is illustrated in Table 1. Drug pharmacodynamics refers to the drug dose–response relationship and remains the least studied aspect of many drugs used in newborns.¹ It is important to have a knowledge of these unique differences in pharmacokinetics and pharmacodynamics in neonates. With that knowledge, the nurse can better understand and predict the newborn's responses to drug therapy. The maturational limitations in this vulnerable population render newborns more susceptible to drug administration mishaps, adverse reactions, and toxic exposures. Application of neonatal pharmacokinetic principles throughout the course of individual drug therapies can reduce the likelihood of any of these mishaps. The purpose of this column is to discuss important principles of neonatal pharmacokinetics as they relate to clinical care of the term newborn and premature infant. Figure 1 illustrates the conceptual definitions of pharmacokinetics and pharmacodynamics and the relationship between the two.