Tacrolimus once-daily formulation in the prophylaxis of transplant rejection in renal or liver allograft recipients: a viewpoint by Helio Tedesco Silva Jr

Population pharmacokinetic model and Bayesian estimator for two tacrolimus formulations--twice daily Prograf and once daily Advagraf

AIM

To investigate the differences in the pharmacokinetics of Prograf and the prolonged release formulation Advagraf and to develop a Bayesian estimator to estimate tacrolimus inter-dose area under the curve (AUC) in renal transplant patients receiving either Prograf or Advagraf.

METHODS

Tacrolimus concentration-time profiles were collected, in adult renal transplant recipients, at weeks 1 and 2, and at months 1, 3 and 6 post-transplantation from 32 Prograf treated patients, and one profile was collected from 41 Advagraf patients more than 12 months post-transplantation. Population pharmacokinetic (popPK) parameters were estimated using nonmem. In a second step, the popPK model was used to develop a single Bayesian estimator for the two tacrolimus formulations.

RESULTS

A two-compartment model with Erlang absorption (n= 3) and first-order elimination best described the data. In Advagraf patients, a bimodal distribution was observed for the absorption rate constant (K(tr) ): one group with a K(tr) similar to that of Prograf treated patients and the other group with a slower absorption. A mixture model for K(tr) was tested to describe this bimodal distribution. However, the data were best described by the nonmixture model including covariates (cytochrome P450 3A5, haematocrit and drug formulation). Using this model and tacrolimus concentrations measured at 0, 1 and 3h post-dose, the Bayesian estimator could estimate tacrolimus AUC accurately (bias = 0.1%) and with good precision (8.6%).

CONCLUSIONS

The single Bayesian estimator developed yields good predictive performance for estimation of individual tacrolimus inter-dose AUC in Prograf and Advagraf treated patients and is suitable for clinical practice.

Optimizing medication adherence: an ongoing opportunity to improve outcomes after kidney transplantation

Nonadherence of transplant recipients to prescribed medical regimens has been identified as a major cause of allograft failure. Although recent studies offer new insight into the clinical phenotypes of nonadherence, advances in defining risk factors and appropriate interventions have been limited because of variable definitions, inadequate clinical metrics, and the challenges associated with healthcare delivery. Significant nonadherence is estimated to occur in 22% of renal allograft recipients and may be a component of allograft loss in approximately 36% of patients. It is associated with increased incidence of rejection (acute and chronic) and, consequently, shortened renal allograft survival, requiring reinstitution of costly chronic renal replacement therapy with an incumbent effect on morbidity and mortality. The economic effect of nonadherence approaches similar magnitude. Identification of risk factors, coupled with measures that effectively address them, can have a positive effect at many levels--medically, socially, and economically. Further advances are likely to be dependent on improving interactions between patients and caregivers, broadening immunosuppressant availability, and newer therapeutics that move toward simpler regimens.