Economic Impact and Long-Term Graft Outcomes of Mycophenolate Mofetil Dosage Modifications Following Gastrointestinal Complications in Renal Transplant Recipients

Introduction: Gastrointestinal (GI) complications are common following renal transplantation. Discontinuing or reducing the dosage of mycophenolate mofetil can improve GI tolerability but adversely affect graft outcomes. This analysis was undertaken to assess the 3-year economic and clinical impact of mycophenolate mofetil dosage modifications or discontinuation following post-transplant GI events compared with no dosage modification. Methods: Adult renal transplant recipients with a Medicare-covered mycophenolate mofetil prescription at the time of GI complication between 1995 and 2000 were drawn from the US Renal Data System (USRDS). The 3-year graft survival rates after first diagnosis of a GI complication were obtained in four cohorts of patients according to mycophenolate mofetil administration within 6 months of initial GI diagnosis: (i) no dosage change in mycophenolate mofetil (NC); (ii) one or more episodes of mycophenolate mofetil dosage reduction <50% of the initial dosage, lasting >30 days (DR <50%); (iii) one or more episodes of mycophenolate mofetil dosage reduction >= 50% of the initial dosage, lasting >30 days (DR >= 50%); and (iv) one or more episodes of mycophenolate mofetil discontinuation >30 days (DC). Two multivariate models were used to estimate the association between DR and DC and graft survival <6 months after GI diagnosis and 6-36 months after diagnosis. In each cohort, Medicare costs for maintaining a patient with stable function were calculated using regression and were augmented with cost of graft failure, resumed maintenance dialysis and death post-graft loss using Medicare data supplied by the USRDS. Survival and cost outcomes were integrated in a 3-year Markov model with 6-month cycles. The perspective was that of Medicare, and costs and outcomes were discounted by 3% per annum. Results: Adult patients (n = 3589) with a mycophenolate mofetil prescription at time of diagnosis of GI event were identified: NC=2230 (62.1%): DR <50% = 247 (6.9%); DR >= 50% = 348 (9.7%); and DC = 764 (21.3%). In the first 6 months after GI diagnosis, DC was associated with increased risk of graft failure (hazard ratio [HR] 3.20; 95% CI 1.71, 5.99; p < 0.0001). During the period 6-36 months after GI diagnosis, the HR for graft loss was higher for the DR >= 50% group (HR 1.32; 95% CI 1.02, 1.70; p < 0.05) and DC group (HR 1.35; 95% CI 1.09, 1.69; p < 0.01) relative to the NC group. Expected 3-year cumulative Medicare costs per patient were $US68 495 for the NC and DR <50% groups, $US70 886 for the DR >= 50% group, $US79 015 for the DC group and $US70 967 overall. Respective QALYs were 2.32, 2.30, 2.27 and 2.31. In sensitivity analysis, reducing the rate of DR and DC by 25% would have lowered expected costs by $US2.2 million in the study population and increased QALYs by 11.2. Monte Carlo simulation indicated a 93% probability that such reduction in the relative risk of mycophenolate mofetil DR/DC was cost saving or cost neutral. Conclusion: Dosage reduction or discontinuation of mycophenolate mofetil in the first 6 months after diagnosis of GI complications is associated with significantly increased risk of graft failure and increased healthcare costs in adult renal transplant recipients.