592 BIOL PSYCHIATRY 1990;27:592-600 Plasma Dexamethasone Levels in Children Given the Dexamethasone Suppression Test Michael W. Naylor, John F. Greden, and Norman E. Alessi To determine whether chi'~dre~ who demonstrate dexamethasone suppression test (DST) nonsuppression have l~¢e~ ~plasma dexamethasone levels than DST suppressors, we administered the DST to 73 patients ranging in age fiom 5-14 years. Plasma dexameth- asone levels and postdexamethasone cortisol levels were measured at 4:00 PM on day 2. We found: (1) DST nonsuppressors had significantly lower plasma dexamethasone levels (p < 0.03) than suppressors; similar trends were observed when the population was divided into depressed and nondepressed patients; (2) mglm2 dose of de:~amethasone was directly correlated with plasma dexamethasone ( p < 0.003) and inversely correlated with postdexamethasone plasma cortisol levels (p < 0.04); and (3) a statistically significant inverse correlation between plasma dexamethasone levels and postdexamethasone cortisol levels (p < 0.04). Our findings show that plasma dexamethasone levels are important in evaluating DST results in psychiatrically disturbed children and suggest that dexa- methasone dosage j r use in the DST in children might be better calculated in terms of body surface area. Introduction Plasma dexamethasone levels are an important variable in understanding hypothalamic- pituitary-adrenal (HPA) axis dysregulation in psychiatrically disturbed adults. Investi- gators have found that depressed adults who are nonsuppressors on the dexamethasone suppression test (DST) have significantly lower plasma dexamethasone concentrations than depressed patients and control subjects who are DST suppressors (Johnson et al. 1984; Arana et al. 1984; Maguire et al. 1987). Several explanations have been advanced for this observation. Lowy and Meltzer (1987) raised the possibility that bioavailability of dexamethasone pla3s ,~ ma~or r~!e in determining DST suppressor status and have suggested that simultaneous measurement of plasma dexamethasone and cortisol levels are needed to evaluate DST results. Alternatively, Holsboer and associates (1986a and b) concluded that the low plasma dexamethasone levels in nonsuppressing adult depres- sives were due to accelerated metabolism of dexamethasone rather than impaired bio- availability, and suggested that the abnormality of glucocorticoid nactabolism in depres- sives with DST nonsuppression is state-dependent. Although the plasma dexamethasone variable has not been studied in children, the From the University of Michigan Department of Psychiatry, Child and Adolescent Psychiatric Hospital (M.W.N., N.E.A.) and the Michigan Depression Program (J.F.G.), University of Michigan, Ann Arbor, Michigan. Address reprint requests to Dr. Michael W. Naylor, Department of Psychiatry, Box 0706, 1500 East Medical Center Drive, Ann Arbor, M148109-0706. Received October 20, 1988; revised January 13, 1989. 0006-3223/90/$03.50 © 1990 Society of Biological Psychiatry