Developmental pharmacology of opioids

Recognition of the need for alternative analgesic regimens for managing neonatal and childhood pain has led to a rich literature concerning the ways in which early life pain differs from that at older ages. As in adults, opiates are often considered the gold-standard analgesic class of drugs, of which morphine is the prototypical agent. There is a wealth of data detailing clinical observations, measurements, and interventions with regard to the use of opioids in treating pain in children. Studies in the early part of this century have highlighted that, in humans, age is an important factor that influences the morphine requirement of neonates following surgery, and dose requirements are influenced by both pharmacokinetic and pharmacodynamic factors. Laboratory studies have extended our understanding of changes within the peripheral and central nervous systems that underlie alterations in nociception in early life. This chapter will review what is currently known about the actions of opioids upon nociceptive and nociresponsive elements of the nervous system in early life, how they differ from adult responses, and ask whether manipulating endogenous opioid systems in early life may have consequences on neurodevelopment.