Jolanta Kamińska, Maciej Głyda, Joanna Sobiak, Maria Chrzanowska above or below 60 ml/min in our study, because the group with impaired renal function included patients with moderate as well as with severe graft dysfunction. Nevertheless, our study showed higher MPA C0 values in patients with Ccr < 60 ml/ min, which may indicate intensified enterohepatic recirculation in patients with impaired renal function as found in the study by Mohammadpur et al. [18]. Proteinuria may also be considered as a factor influencing MPA and MPAG PK parameters. Nae- sens et al. [21] demonstrated correlations between MPA PK parameters and proteinuria. However, in our study in the multivariate analysis no relations between MPA and MPAG PK parameters were observed. It may be due to the small number of patients (n = 9) with proteins determined in urine. In conclusion, renal failure, irrespective of immunosuppressive regimen, influences the MPAG PK parameters and MPA C0 by increasing the val- ues in patients with impaired renal function. The results of our study indicate that solely MPA C0 determination in patients receiving MMF may be insufficient in clinical practice because of great inter-patient variability of this PK parameter caused mainly by enterohepatic recirculation. It may lead to wrong decisions concerning the pharmacother- apy, particularly in patients with impaired renal function. It seems to us that the monitoring of MPA and MPAG AUC may allow MMF dosage regimens to be optimized, and as a result improve the early prevention of adverse effects in these patients. Acknowledgments This study was supported by Grant No. 501-02- 03306413-02324-50382 from Poznan University of Medical Sciences. The authors declare no conflict of interest. R e f e r e n c e s 1. Morris RG. 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