![]() ![]() Pupil diameter measures also (1) correlate significantly with self-report and observer-rated measures of withdrawal (e.g., Fraser et al., 1954 Higgins et al., 1985 Jasinski et al., 1978), (2) are an index of the severity of tolerance (e.g., Higgins et al., 1985), and (3) differentiate between dependent and nondependent populations (e.g., Tress et al., 1978). Consistent with this profile, pupil constriction is four-fold greater and lasts significantly longer after 30 mg of oral methadone vs. For example, milligram for milligram, methadone is more potent than morphine and has a longer duration of action. The magnitude and time course of pupillary effects vary according to the pharmacodynamics and pharmacokinetics of the opioid. For example, opioid administration results in pupil constriction, followed by predictable, progressive dilation over time as the drug is metabolized (e.g., Fraser and Isbell, 1952a 1952b Fraser et al., 1954). In adults, pupil diameter is a frequently assessed objective index of the pharmacodynamic effects of opioids (see review by Loewenfeld, 1999). Increasing calls for the development of more objective and sensitive measures of NAS ( Jones, 2011 O’Brien et al., 2004 Velez et al., 2009) prompted us to investigate pupil diameter as a potential marker of infant response to opioid administration. For example, there are concerns regarding the lack of rigorous psychometric testing to establish reliability and validity as well as the lengthy training and administration times required to accurately administer most observer-rated scales ( American Academy of Pediatrics, 1998 Jones, 2011 O’Brien et al., 2004). While the development and dissemination of observer-rated scales was an important advance in the assessment and treatment of NAS, the scales have some shortcomings that limit their utility. The most commonly used observer-rated scales (e.g., Finnegan Scale, Lipsitz tool) were developed and underwent rudimentary validation testing in the mid-1970s, driven by dramatic increases in the number of opioid-exposed neonates as a result of an epidemic of heroin use ( Hughes and Rieche, 1995). The only tools currently available for evaluating the need for and effectiveness of pharmacological treatment for NAS are observer-rated scales. A recent report conservatively estimated that the total US hospital charges to care for infants with NAS currently exceed $700 million per year ( Patrick et al., 2012). At least 50% will require pharmacological treatment to manage their NAS ( Cleary et al., 2010 Jones et al., submitted), resulting in hospital stays of 8–79 days ( Kraft et al., 2011) and dramatically increasing costs. Extended hospitalization (4 days minimum) is recommended to monitor NAS in all opioid-exposed neonates. Both illicit and licit opioid dependence during pregnancy is associated with adverse consequences for the neonate, including a high incidence of neonatal abstinence syndrome (NAS), a disorder characterized by central nervous system hyperirritability, gastrointestinal dysfunction, respiratory distress, and autonomic dysregulation ( Finnegan et al., 1975). Prenatal opioid exposure is a rapidly growing public health problem due to continued heroin abuse and alarming increases in prescription opioid abuse by pregnant women ( Patrick et al., 2012).
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