Safety profile comparing azathioprine and mycophenolate in kidney transplant recipients receiving tacrolimus and corticosteroids.

BACKGROUND: Debate is increasing on whether mycophenolic acid (MPA) provides survival benefits comparable to azathioprine (AZA) after renal transplantation.

METHODS: This retrospective cohort study compared safety and efficacy of AZA (n = 662) vs. MPA (n = 267) in low-immunologic-risk kidney transplant recipients (KTR) receiving tacrolimus (TAC) and steroids between 1998 and 2007. Primary outcomes were treatment discontinuation and infection. Secondary endpoints included survival free from biopsy-proven acute rejection, graft loss, death, and renal function.

RESULTS: The 5-year survival free of treatment discontinuation was higher in the MPA compared to the AZA group (74.1% vs. 60.3%, P < 0.001). MPA was discontinued exclusively because of adverse events (16.4%), while AZA was discontinued primarily for lack of efficacy (21.2%). In univariable analysis, MPA was associated with higher incidence of total (561.5 vs. 667.5 episodes/1000 person-year, P < 0.001), bacterial (167 vs. 158 episodes/1000 person-years, P = 0.001), and viral infections (83.2 vs. 100.4 episodes/1000 person-years, P = 0.001), but this association was not confirmed in multivariable analysis. Over 29% of viral infections in the AZA group occurred after conversion to MPA. A high incidence of tuberculosis was observed (2.9 episodes/1000 person-years) with a higher incidence (but not a statistically significant difference) in the AZA group. No significant differences were found in patient survival (90% vs. 89%, P = 0.78) or graft survival (81% vs. 77.7%, P = 0.08), but infection accounted for >50% of all deaths.

CONCLUSION: The type of antimetabolite, AZA or MPA, was not independently associated with any safety or efficacy outcome 5 years after transplantation, suggesting that AZA is still a viable option for low-risk KTR receiving TAC and steroids.