Simple methods for estimation of prednisone intake and metabolism

For patients treated with high doses of prednisone (over 40 mg/day) laboratory follow-up is important, particularly when the therapeutic response does not correlate with the dose of prednisone prescribed. Taking advantage of the similarity in structure of prednisone to cortisone and of prednisone to cortisol we evaluated simple, inexpensive methods for the assessment of prednisone and prednisolone intake and bio-availability. Free urinary prednisolone was estimated by radioimmunoassay for cortisol and found to be linearly correlated with the dose of prednisone administered (r = 0.9310). Levels of free prednisolone were 6.5-11% of the dose of prednisone per day. Free and metabolized prednisone and prednisolone were estimated as 17-OHCS in the 24-hr urine collection. Total, conjugated and free 17-OHCS were linearly correlated with the dose of prednisone, the best correlation being with total 17-OHCS (r = 0.9060). About 40% of the prednisone administered was secreted as total 17-OHCS.