Monitoring Nonadherence and Acute Rejection With Variation in Blood Immunosuppressant Levels in Pediatric Renal Transplantation

Acute rejection associated with medication nonadherence is a major cause of allograft loss in pediatric kidney transplant patients. There is currently no reliable method to detect medication nonadherence and prevent allograft rejection. In 46 pediatric patients who underwent renal transplantation between 2002 and 2003, the variation of serum drug levels was studied as a potential objective tool to monitor medication nonadherence. Tacrolimus (TAC) and mycophenolic acid (MPA) trough levels were measured from 1 to 12 months posttransplant, and standard deviation (SD) and percent coefficient of variation (CV%) were calculated. Because SD increased as mean trough levels rose, CV% (CV%=SD/mean multiplied by 100%) was used to eliminate this confounding effect. Ten of 46 patients had biopsy-proven rejection. The median TAC CV% was 53.4% in patients with biopsy-proven rejection, which was significantly higher than 30% in those without rejection (P=0.005). Median MPA CV% was 51.9% in patients without rejection and 45.1% in patients with rejection (P=NS). High TAC CV% correlated with increased risk for rejection, whereas MPA CV% did not. The TAC CV% seems to be a useful and superior marker, compared with SD alone, for assessing medication nonadherence and the possibility of allograft rejection in pediatric renal transplantation.