[Pharmacokinetics of prednisolone (PSL) during PSL treatment. I. PSL pharmacokinetics during daily PSL treatment].

We studied the pharmacokinetics of prednisolone (PSL) in eight patients (two each with subacute thyroiditis, systemic lupus erythematosus, and nephrotic syndrome: and one each of Crohn's disease and aortitis syndrome) before and during the daily treatment with PSL(duration of 0.5-4.0 months with the mean of 1.9 months; total amount of 0.3-8.0 g with the mean of 2.8 g). PSL was measured by radioimmunoassay. Cmax, Tmax and AUCp.o. were calculated on the single oral administration of 40 mg PSL, and T1/2 beta, Vd and MCR were calculated when 25.6 mg of PSL sodium succinate (equivalent to 20 mg of PSL) was injected intravenously. Bioavailability was calculated by the ratio of AUCp.o. X PSL i.v. dose to AUCi.v. X PSL p.o. dose. With the oral administration, there was no difference in Cmax, Tmax and AUCp.o. between before and during the treatment, respectively. With the intravenous PSL administration, significant increase of AUCi.v. (p less than 0.01), significant decrease of MCR (p less than 0.01), significant elongation of T1/2 beta (p less than 0.05), and significant decrease of the bioavailability (p less than 0.001) were found in the PSL treatment period compared with before the treatment, but no significance was found in Vd between, before, and during the treatment. There was no difference in these changes in parameters among the diseases. Nor were any correlations found between the changes in these parameters of T1/2 beta, MCR or bioavailability and the duration or the total amount of PSL administered, respectively. These results indicate that the decreased MCR, elongated T1/2 beta and the decreased bioavailability of PSL were brought about by daily administration of PSL, regardless of the kind of diseases, or the total amount or the duration of PSL administration.