Pharmacokinetics and delta1-cortienic acid excretion after intravenous administration of prednisolone and loteprednol etabonate in rats.

Abstract

Detailed pharmacokinetic (PK) studies in rats were performed (i)to compare the PK of prednisolone (PRN) and loteprednol etabonate (LE, a soft corticosteroid) as well as their common inactive metabolite delta1-cortienic acid (delta1-CA), (ii) to investigate the excretion of delta1-CA after PRN and LE administration, and (iii) to investigate the effect of delta1-unsaturation on the excretion of delta1-CA versus CA. Following a 10 mg x kg(-1) intravenous bolus dose, the total clearance (CL(tot)) of PRN (27.0 +/- 1.4 mL x min(-1) kg(-1)) was significantly lower than that of LE (67.4 +/- 11.6 mL x min(-1) kg(-1)) or delta1-CA (53.8 +/- 1.4 mL x min(-1) kg(-1)) indicating that the metabolism/elimination of PRN in the liver (primarily, conjugation) may be less efficient than that of LE (primarily, hydrolysis) or delta1-CA (unchanged). The volume of distribution (Vd(ss)) of PRN (823 +/- 78 mL x kg(-1)) was significantly lower than that of LE (3078 +/- 79 mL x kg(-1)) indicating that LE is more distributed to lipophilic tissues. Excretion studies have confirmed that delta1-CA is indeed a metabolite of PRN. After intravenous injection of 10 mg x kg(-1), less than 1% of the administered PRN was excreted as delta1-CA by 4 h (0.38 +/- 0.10% in bile and 0.18 +/- 0.04% in urine), significantly less than for LE (17.01 +/- 2.09% in bile and 2.53 +/- 1.17% in urine) indicating that extent of this metabolic transformation can indeed be affected by molecular design. At doses of 100 mg/kg, the proportion of delta1-CA excreted after PRN administration (0.12 +/- 0.03% in bile and 0.19 +/- 0.03% in urine) was similar to that of CA excreted after hydrocortisone administration (0.11 +/- 0.03% in bile and 0.22 +/- 0.04% in urine) indicating that the presence of the delta1 double bond (delta1-unsaturation) does not affect significantly this metabolic conversion.