Introduction: Recently, mTOR inhibitor base regimen has emerging as a main treatment strategy to avert calcineurin inhibitor induced nephrotoxicity in solid organ transplant patients. Results from different centers have confirmed the beneficial effect of this approach in patients with initial kidney creatinine clearance greater than 40ml/min. However, proteinuria is increasingly noticed as a complication of mTOR inhibitor application. The pathological processes responsible for this adverse effect are not completely understood so far. To see if conversion timing will affect the incidence of proteinuria in these patients, we conduct the following study. Methods: Inclusion criteria: kidney transplant recipients regularly follow-up in our clinic fulfilled the following criteria were recruited into this study: 1, creatinine clearance greater than 40ml/min; 2, daily urine protein loss less than 800mg. Exclusion criteria: patients with multiple organ transplantation, pregnancy, poor compliance or allergy to mTOR inhibitor are excluded. Once included, patients were put on everolimus 1.5mg per day. The dosage of everolimus was adjusted to keep their trough serum level between 3-8ng/ml. Their calcineurin inhibitor was reduced by half initially and tapered to the minimal dose within 2-4 weeks i.e. cyclosporin 25mg/ day or tacrolimus 0.5mg/day. Mycophenolic acid dosage were cut immediately by half and tapered as necessary, while steroid dosage was kept at 5mg per day or less. Graft function, hemogram, daily urine protein and biochemistry data including fasting sugar, liver function and lipid profiles were checked regularly. Results: In total, 18 patients were recruited into this study. After follow-up for 6 months, their creatinine clearance improved from 72.4± 5.6ml/min to 85.3± 9.8ml/min. Further analysis showed that five out of seven patients with transplantation duration longer than one year had aggravated proteinuria, which is defined as increase daily urine protein loss from their baseline level for more than 500mg. In eleven patients with transplantation duration less than one year, none has aggravated proteinuria after receiving everolimus treatment. Other factors such as underlying disease, age, baseline graft function, baseline proteinuria, lipid profiles and fasting sugar were all similar in both groups. Conclusion: In this preliminary study, we found that transplantation duration longer than one year is an important risk factor for the development of proteinuria in patients receiving mTOR inhibitor treatment.
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