The effect of dexamethasone dosage upon plasma cortisol and dexamethasone during the DST

To investigate the effect of dexamethasone dosage upon the outcome of the dexamethasone suppression test (DST) and the role of concurrent plasma dexamethasone concentrations, four different dexamethasone dosages were administered to 119 hospitalized depressed patients (0.5 mg: n = 12; 1.0 mg: n = 30; 1.5 mg: n = 42; 2.0 mg: n = 35). Independent of the dosage, dexamethasone plasma concentrations at 4.00 p.m. were lower in DST non-suppressors than in suppressors, although differences were statistically significant only for the 1.5-mg and 2.0-mg dosages. Our findings confirm recent reports that the actual plasma concentration of dexamethasone at 4.00 p.m. does not determine DST outcome.