DOSING, BIOAVAILABILITY, AND DRUG RESPONSE6

When pediatric labeling information is lacking, pediatricians often refer to the available scientific literature to estimate dosing for children. If such studies exist, they are frequently based on very small, selected populations. Dr. Ward gave a neonatologist’s perspective on treating newborns, whom he views as the most susceptible pediatric patients. He provided several examples of how pharmacokinetics and organ function (such as that of the heart and the kidneys) vary in important ways among a 23-week premature infant, a 30-week premature infant, and a 40-week full-term infant. He also cited studies that have revealed ethnic variations in the distribution of certain enzymes that cause faster or slower metabolism of drugs. Moving from dose guessing to informed prescribing will require additional studies of the pharmacokinetics, safety, and efficacy of new drugs and older, off-patent drugs. Those studies will need to be coupled with the study of developmental variations relevant to dosing, such as changes in drug clearance, during the first few months after birth and beyond.

In responding to Dr. Ward’s presentation, Dr. Snodgrass described some shortcomings in the existing framework for pediatric drug use. Although the current system offers a good mechanism for testing on-patent drugs (see the discussion of this issue in Chapter 2), it falls short for older, off-patent drugs. With a common drug such as morphine, little information is available on optimal use and basic pharmacokinetics in different age groups. Dr. Snodgrass also expressed concern that pediatricians lack a good evidence-based reference for making prescription decisions. For example, there is disagreement on whether dosing should be based on weight or surface area. Dr. Snodgrass further suggested that dissemination of information to physicians could be improved so they can make the best choices in prescribing medications for individual patients. Finally, Dr. Snodgrass and others seconded Dr. Giacoia’s emphasis on the importance of the taste and formulation of a drug to adherence in pediatric patients—more so than is the case with adults.

6

This section is based on the presentation of Dr. Robert Ward, Director, Pediatric Pharmacology Program, University of Utah.



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