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Analgesics for Neonates and Young Infants
Acetaminophen can be safely administered to neonates and infants without concern for hepatotoxicity when given for short courses at the recommended doses.44 Acetaminophen can be given to augment analgesia.
The use of opioids in young infants requires special consideration and expertise. Young infants, especially premature babies or those who have necrologic abnormalities or pulmonary disease, are susceptible to apnea and respiratory depression when systemic opioids are used.385 The infant's metabolism is altered so that the elimination half-life is longer and the blood-brain barrier is more permeable.96; 289 Both factors result in young infants having higher in-brain concentrations of opioids for a given dose than do mature infants or adults. Intensive monitoring is reasonable up to about 1 year of age for nonventilated infants who are receiving opioids because extreme sedation and decreased respiratory effort may be difficult to assess. Institutions where neonates and infants are treated for cancer should train personnel in the effective and safe administration of analgesia and provide appropriate technologies for monitoring.
Some evidence suggests that the clearance of opioids increases rapidly over the first few weeks of life and approaches adult levels by the time the infant is a few months old.203; 262 Because available data are based on small numbers of infants, many practitioners reduce the initial dose and use intensive monitoring for infants up to 6 months of age; this age is arbitrary and represents a cautious interpretation of the literature.
Although further research is necessary, apnea and respiratory depression appear to be dose related.262 For nonventilated infants under 6 months of age, the initial opioid dose, calculated in milligrams per kilogram, should be about one-fourth to one-third of the dose recommended for older infants and children. For example, 0.03 mg/kg of morphine could be used instead of the traditional 0.1 mg/kg. Careful assessment is necessary so that the optimal dose and interval of administration can be determined from clinical parameters (e.g., when pain occurs and whether the infant appeared comfortable). Many infants have inadequate pain relief after the initial small dose and require upward titration, sometimes to doses equivalent to those used for older children. Continuous infusions can be used as long as the infusion begins with a conservative starting dose, which is then titrated upward until pain is relieved.
Aggressive monitoring, when necessary, should include frequent assessments and close observation of heart and respiratory rates, respiratory effort, blood pressure, and level of alertness as determined by responsiveness to stimuli. Frequent or continuous assessment of arterial oxygen saturation with pulse oximetry is a valuable adjunct to clinical observation. Because of delayed absorption, opioid levels in serum may increase many hours after a one-time intramuscular or subcutaneous dose in infants who are opioid naive; monitoring, therefore, should be continued for 12 hours after an opioid dose.259
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