A radioimmunoassay procedure for dexamethasone: plasma and urine levels in man.

A sensitive and precise dexamethasone radioimmunoassay method was applied to the determination of dexamethasone levels in the plasma and urine of human subjects who had received small doses of the drug by mouth. While the method can be applied directly to plasma, urine has to be diluted before assay. Very little cross-reaction was observed with two possible metabolites of dexamethasone. Both in the healthy subjects and in the group of patients investigated rapid absorption of dexamethasone from the gastrointestinal tract was observed. However, there appeared to be a large individual variation in the plasma concentration of the drug obtained after doses of the same size.