Prolonged steroid therapy for early chronic lung disease in very low birth weight (VLBW) infants is associated with HPA axis suppression. The duration and specific location of this suppression is not yet known. We evaluated the HPA axis in ten VLBW infants before and 48 hrs after a prolonged (14-42 day) DEX course. Seven of these infants underwent serial testing in the Clinical Research Center to evaluate recovery of the HPA axis. Adrenal function was evaluated by cortisol response to synthetic adrenocorticotropin(ACTH). Combined HPA axis function was tested using 3 hour metyrapone stimulation. Data was analyzed using paired t-tests.

Baseline cortisol values were higher before DEX (32.6 ± 7.4μg/dL; mean ± SEM) than after (10.1 ± 4.5μg/dL; p < 0.02). ACTH-stimulated cortisol levels were also higher before DEX therapy (24.3± 2.0 versus 10.6 ± 2.6μg/dL; p < 0.001). 11-deoxycortisol(DOC) response to metyrapone dropped from 11.1 ± 0.5μg/dL to 4.7± 1.0μg/dL after Dex(p < 0.0001). Adrenal response to ACTH was abnormal in only 7/10 infants after Dex, while metyrapone testing suggested HPA axis suppression in 9/10 infants. Analysis of longitudinal testing suggests that adrenal suppression may be short-lived, with 4/7 patients having a normal cortisol response to ACTH within one month of completing DEX therapy. Recovery of higher HPA axis centers was more delayed with only 2/7 patients demonstrating a normal response to metyrapone within one month of Dex. Of note, both of these infants received truncated Dex courses.

These results confirm that HPA axis suppression results from long-term DEX therapy. Furthermore, function of the adrenal gland appears to recover earlier than higher centers in the axis. We conclude that HPA axis recovery is most reliably tested using 11-DOC response to a single dose of metyrapone in VLBW infants after prolonged DEX therapy.