Background: Some drugs used for sedation and anesthesia produce histopathologic central nervous system changes in juvenile animal models. These observations have raised concerns regarding the use of these drugs in pediatric patients. We summarized the findings in developing animals and describe the steps that the Food and Drug Administration (FDA) and others are taking to assess potential risks in pediatric patients. The FDA views this communication as opening a dialog with the anesthesia community to address this issue.
Methods: We reviewed the available animal studies literature examining the potential neurotoxic effects of commonly used anesthetic drugs on the developing brain. The search strategy involved crossing the keywords neurotoxic and neuroapoptosis with the following general and specific terms: anesthetic, N-methyl-d-aspartate (NMDA), ketamine, midazolam, lorazepam, fentanyl, methadone, morphine, meperidine, isoflurane, nitrous oxide, sevoflurane, halothane, enflurane, desflurane, propofol, etomidate, barbiturate, methoxyflurane, and chloral hydrate. We summarized several studies sponsored by the FDA in rats and monkeys, initially examining the potential for ketamine, as a prototypical agent, to induce neurodegeneration in the developing brain.
Results: Numerous animal studies in rodents indicate that NMDA receptor antagonists, including ketamine, induce neurodegeneration in the developing brain. The effects of ketamine are dose dependent. The data suggest that limiting exposure limits the potential for neurodegeneration. There is also evidence that other general anesthetics, such as isoflurane, can induce neurodegeneration in rodent models, which may be exacerbated by concurrent administration of midazolam or nitrous oxide. There are very few studies that have examined the potential functional consequences of the neurodegeneration noted in the animal models. However, the studies that have been reported suggest subtle, but prolonged, behavioral changes in rodents. Although the doses and durations of ketamine exposure that resulted in neurodegeneration were slightly larger than those used in the clinical setting, those associated with isoflurane were not. There are insufficient human data to either support or refute the clinical applicability of these findings.
Conclusions: Animal studies suggest that neurodegeneration, with possible cognitive sequelae, is a potential long-term risk of anesthetics in neonatal and young pediatric patients. The existing nonclinical data implicate not only NMDA-receptor antagonists, but also drugs that potentiate gamma-aminobutyric acid signal transduction, as potentially neurotoxic to the developing brain. The potential for the combination of drugs that have activity at both receptor systems or that can induce more or less neurotoxicity is not clear; however, recent nonclinical data suggest that some combinations may be more neurotoxic than the individual components. The lack of information to date precludes the ability to designate any one anesthetic agent or regimen as safer than any other. Ongoing studies in juvenile animals should provide additional information regarding the risks. The FDA anticipates working with the anesthesia community and pharmaceutical industry to develop strategies for further assessing the safety of anesthetics in neonates and young children, and for providing data to guide clinicians in making the most informed decisions possible when choosing anesthetic regimens for their pediatric patients.