Prednisolone disposition in steroid-dependent asthmatics.

A 40-mg intravenous dose of prednisolone was given as prednisolone phosphate to seven severe steroid-dependent asthmatics and to 13 healthy volunteers to determine if the large prednisone requirements of these patients were a function of the disease, cellular response, or rapid clearance of prednisolone. Plasma concentrations of prednisolone, prednisone, and cortisol were determined by high-performance liquid chromatography over an 8-hr test period. Circulating eosinophil concentrations were monitored concurrently. The apparent half-lifes of prednisolone in the asthmatics and normals were 3.33 +/- 0.71 and 3.25 +/- 0.58 hr (mean +/- SD). The apparent plasma clearances of prednisolone were 201 +/- 54 and 198 +/- 38 ml/min/1.73 m2 and the apparent volumes of distribution were 50.8 +/- 11.7 and 53.5 +/- 13.5 L/1.73 m2 for the asthmatic and normal groups, respectively. When the concentration-dependent binding of prednisolone to plasma protein was examined, no differences in the apparent clearances of unbound drug were found between the two groups. The eosinopenic response to prednisolone was similar in the steroid-dependent asthmatics and healthy normal volunteers. These studies indicate that binding, distribution, and clearance of prednisolone are not responsible for the large prednisone requirement of some steroid-dependent asthmatics. Differences in steroid-receptor sensitivity or in severity or pathophysiology of the disease state more likely account for the need for large prednisone dosages in these patients.