Effects of probenecid on the pharmacokinetics of mizoribine and co-administration of the two drugs in patients with nephrotic syndrome.

Probenecid (PRB) is an agent that reduces the systemic level of uric acid, and has the ability to inhibit the renal tubular secretion of agents that are co-administered with it. In this study, we evaluated the effects of PRB co-administered with mizoribine (MZR) on the pharmacokinetics (PK) of MZR in 12 patients with nephrotic syndrome. The elimination rate constant (kel) was used as an indicator of changes in the PK of MZR when the secretion of MZR was inhibited by co-administration of PRB, in order to determine the extent to which MZR was influenced by PRB. In 4 of the 12 patients studied, kel decreased and the biological half-life (t1/2) of MZR was prolonged when co-administered with PRB, in comparison with the values when MZR was used alone, thus revealing that the PK of MZR was influenced by PRB. Co-administration of PRB with MZR appears to be effective in prolonging the biological half-life of MZR and enhancing its effect in patients with nephrotic syndrome, although further studies will be required to determine the optimal dosage of PRB and renoprotective effects.