*Purpose: Registration trials using old sandimmune formulation of cyclosporine (CsA) led to the general idea that Mycophenolate Mofetil (MMF) prevents acute cellular rejection (ACR) more effectively than Azathioprine (AZA), but multiple trials with standard-dose of more stable microemulsion formulation of CsA (Neoral) showed no difference between the two drugs. The safety/efficacy of MMF and AZA in kidney transplant recipients on steroid-free, low-dose CsA Neoral is unknown.

*Methods: The ATHENA trial (NCT00494741) wasarandomized, prospective, multicenter trial comparing THe Effect on chronic allograft Nephropathy prevention of mycophenolate mofetil versus Azathioprine as the sole immunosuppressive therapy for kidney transplant recipients. All patients were induced with low-dose Thymo + basiliximab. Patients with stable graft function, no previousACRs and no infiltrates at 1-yr surveillance biopsies underwent CsAtapering to half of the initial dose. Primary endpoint was clinical and subclinical ACRs at 2 years. Analysis was by intention to treat.

*Results: We included 233 patients (119 on MMF and 114 on AZA). During the first 2 years of follow-up, 22 (18.5%) patients in the MMF and 24 (21.1%) in the AZA group experienced at least one biopsy-provenACR (p = 0.72). Twenty-three rejections were detected at surveillance biopsy [13 (10.9%) in the MMF and 10 (8.8%) in the AZA group; p = 0.58]. At 2 yrs, graft function and safety profile were also similar. Forty patients (19 on MMF and 21 on AZA) successfully tapered down CsA doses, with only two of them experiencing ACRs (one per arm). CsA tapering was associated with stable graft function.

*Conclusions: In kidney transplant recipients on low-dose CsAand no steroids, AZA is associated with a similar incidence of biopsy-provenACR and similar safety profile. Due to the lower costs, AZA represents a valuable alternative to MMF also on low-dose maintenance immunosuppression.

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