Objective: We conducted a treatment trial to determine the relative toxicity of FK-506 and cyclosporine A (CSA) in liver transplant recipients.
Design: Between October 1990 and October 1991, 37 patients were enrolled in an open-labeled, randomized study of two immunosuppressive regimens after liver transplantation.
Material and methods: Of the 23 men and 14 women, 20 received FK-506 plus prednisone, and 17 received CSA plus prednisone and azathioprine. Renal function was assessed before and after transplantation (day 1, month 1, month 4, and month 12) by measurements of serum creatinine (SCr) and glomerular filtration rate (GFR) as determined by urinary iothalamate or creatinine clearance (or both). FK-506 trough plasma levels (enzyme immunoassay) were to be maintained between 0.2 and 5.0 ng/mL, and CSA trough blood levels (whole blood high-performance liquid chromatography) were to be maintained between 250 and 400 ng/mL. Severe nephrotoxicity was defined as sudden decreases in urine output to less than 10 mL/h or rapid increases in SCr (more than 0.5 mg/dL daily) that necessitated withdrawal of study medication for more than 48 hours. Mean patient age and values for SCr and GFR were comparable between the two groups at entry.
Results: Both study groups demonstrated a similar deterioration in renal function during a 12-month follow-up, although patients who received FK-506 had a significantly (P < 0.05) lower GFR when measured at 12 months than did patients treated with CSA (45 +/- 4 versus 64 +/- 6 mL/min per body surface area). Mild nephrotoxicity that responded to decreased drug doses was noted in 9 CSA-treated patients (53%) and 10 FK-506-treated patients (50%). Severe nephrotoxicity that necessitated drug withdrawal occurred in only four patients, all of whom were in the FK-506 group. These severe nephrotoxic reactions to FK-506 occurred early after transplantation, often during intravenous administration of the drug, and were not associated with poor liver allograft function or drug levels outside the therapeutic range.
Conclusion: Both FK-506 and CSA are significantly nephrotoxic in liver transplant recipients. In this trial, however, we observed an early development of severe nephrotoxic reactions only in some patients who received FK-506.