Duration of cortisol suppression following a single dose of dexamethasone in healthy volunteers: a randomised double-blind placebo-controlled trial.

The synthetic glucocorticoid dexamethasone is administered to many patients receiving a general anaesthetic to reduce the risk of postoperative nausea and vomiting. Dexamethasone is known to suppress the hypothalamic-pituitary-adrenal axis; however, the duration of this suppression following the standard anti-emetic intravenous dose of 4 to 8 mg used with anaesthesia is unknown. A randomised controlled double-blind crossover trial assessing the effects of 8 mg intravenous dexamethasone versus saline control was performed in ten healthy male volunteers. The adrenal, thyroid and gonadal axes and glucose levels were assessed over a four-day period after dexamethasone administration. All participants had normal baseline hypothalamic-pituitary-adrenal axis function. No difference in cortisol levels was demonstrated at four or eight hours after dexamethasone administration compared with placebo. At 24 hours post dexamethasone, the cortisol had dropped to less than 5% of baseline and returned to normal during the subsequent day. Increased plasma glucose levels were also observed in the dexamethasone group as compared with placebo. A dose of 8 mg of dexamethasone results in significant suppression of the hypothalamic-pituitary-adrenal axis and elevated plasma glucose levels. The cortisol suppression is maximal at approximately 24 hours post dose.