Optimal sparse sampling for estimating ganciclovir/valganciclovir AUC in solid organ transplant patients using NONMEN.

BACKGROUND: Ganciclovir and valganciclovir (GCV/VGCV) are used for the treatment and prophylaxis of cytomegalovirus in solid organ transplant (SOT) patients. An area under the time-concentration curve of 40-50 µg × h/mL is related to efficacy. Therapeutic drug monitoring could prevent suboptimal drug exposure and adverse events, but obtaining full concentration profiles is not feasible. Sampling optimization by developing a reliable and clinically applicable limited sampling strategy (LSS) may simplify dose adjustment. METHODS: An LSS was developed using an original pharmacokinetic (PK) data set of 40 full profiles from 20 adult SOT patients. The LSS was developed based on population and Bayesian prediction approaches. Population PK parameters from a previous model were used for simulation or as priors (NONMEM version 7.2). Median percentage of prediction error and median of absolute percentage prediction error were calculated for plasma clearance (CL) and central compartment distribution volume (V(2)). Bias and precisions were compared using 1-way analysis of variance (SPSSv19.0). RESULTS: Sampling windows were designed according to the PK profile previously observed with the entire set of data. The 4 windows selected were distributed from 0.5 to 1.5 hours, 2 to 3 hours, 4 to 5 hours, and 6 to 8 hours. Predose and concentrations beyond 8 hours were not considered in any case because simulated negative concentrations occurred in both cases. Predicted exposure using 3 sampling times (0.5-1.5, 4-5, and 6-8 hours) showed the best predictive performance, by either the population or Bayesian approaches. Bias and imprecision for CL and V(2) were 0 and 0.60%, and -0.78% and 0.78%, respectively. CONCLUSIONS: GCV/VCG area under the time-concentration curve in SOT patients could be predicted with acceptable accuracy for clinical management and dose individualization using LSS. The estimator of GCV/VGC, using 3 concentrations measured at 0.5-1.5, 4-5, and 6-8 hours after drug intake, could be used for dose adjustment.

Do drug transporter (ABCB1) SNPs and P-glycoprotein function influence cyclosporine and macrolides exposure in renal transplant patients? Results of the pharmacogenomic substudy within the symphony study.

The function of the efflux pump P-glycoprotein (Pgp) and ABCB1 single nucleotide polymorphisms (SNPs) should be considered as important tools to deepen knowledge of drug nephrotoxicity and disposition mechanisms. The aim of this study is to investigate the association of C3435T, G2677T, C1236T, and T129C ABCB1 SNPs with Pgp activity and exposure to different immunosuppressive drugs in renal transplant patients. Patients included in the Symphony Pharmacogenomic substudy were genotyped for ABCB1 SNPs. According to the design, patients were randomized into four immunosuppressive regimens: low and standard dose of cyclosporine (n = 30), tacrolimus (n = 13), and sirolimus (n = 23) concomitantly with mycophenolate and steroids. Pgp activity was evaluated in PBMC using the Rhodamine 123 efflux assay. TT carrier patients on C3435T, G2677T, and C1236T SNPs (Pgp-low pumpers) showed lower Pgp activity than noncarriers. Pgp-high pumpers treated with cyclosporine showed lower values of Pgp function than macrolides. There was a negative correlation between cyclosporine AUC and Pgp activity at 3 months. Results did not show any correlation between tacrolimus and sirolimus AUC and Pgp activity at 3 months. We found an important role of the ABCB1 SNPs Pgp function in CD3(+) peripheral blood lymphocytes from renal transplant recipients. Pgp activity was influenced by cyclosporine but not macrolides exposure.

Early hematopoietic microchimerism predicts clinical outcome after kidney transplantation.

BACKGROUND: The presence of a few circulating donor cells in recipient's blood was first thought to be only an epiphenomenon of solid organ transplantation, also called microchimerism, but several authors have suggested that these circulating cells may contribute to tolerance induction. This study aims to assess the rate of microchimerism after kidney transplantation and determine its influence on acute rejection in a 4-year follow-up. METHODS: A total of 84 single-kidney recipients were included for microchimerism detection and quantification 2, 6, 12, and 18 months after transplantation by specific detection of non-shared STR, VNTR, human leukocyte antigen-A, -B, -DRB1, and SRY alleles. Kinetic establishment of microchimerism was monitored in a double kidney transplanted recipient for 150 min after declamping and after 7 days. RESULTS: Microchimerism was detected in 56.2% of kidney recipients 2 months after transplantation (M2): this fell to 30.1% at 12 months. In renal calcineurin inhibitor-based immunosuppression cohort (n=73), the microchimerism-negative group (n=32) showed 37.9% biopsy-proven acute rejection (BPAR), whereas in the microchimerism-positive group (n=41), no recipient did (P<0.001). Regardless of immunosuppression, BPAR incidence was 35.6% and 4.9%, respectively (P<0.001). Multivariate study showed microchimerism as a protective factor against BPAR (odds ratio: 8.3; 95% confidence interval: 1.8 to 37.9; P = 0.006), blinding other well-known rejection-risk variables. Microchimerism M2 presence did not correlate with a multifactorial critical outcome such as late graft loss. CONCLUSION: Microchimerism was frequent after kidney transplantation and correlated with a significantly lower incidence of rejection. We propose that early microchimerism monitoring could help early detection of low rejection-risk recipients.

Achieving donor-specific hyporesponsiveness is associated with FOXP3+ regulatory T cell recruitment in human renal allograft infiltrates.

Exploring new immunosuppressive strategies inducing donor-specific hyporesponsiveness is an important challenge in transplantation. For this purpose, a careful immune monitoring and graft histology assessment is mandatory. Here, we report the results of a pilot study conducted in twenty renal transplant recipients, analyzing the immunomodulatory effects of a protocol based on induction therapy with rabbit anti-thymocyte globulin low doses, sirolimus, and mofetil mycophenolate. Evolution of donor-specific cellular and humoral alloimmune response, peripheral blood lymphocyte subsets and apoptosis was evaluated. Six-month protocol biopsies were performed to assess histological lesions and presence of FOXP3+ regulatory T cells (Tregs) in interstitial infiltrates. After transplantation, there was an early and transient apoptotic effect, mainly within the CD8+ HLADR+ T cells, combined with a sustained enhancement of CD4+ CD25(+high) lymphocytes in peripheral blood. The incidence of acute rejection was 35%, all steroid sensitive. Importantly, only pretransplant donor-specific cellular alloreactivity could discriminate patients at risk to develop acute rejection. Two thirds of the patients became donor-specific hyporesponders at 6 and 24 mo, and the achievement of this immunologic state was not abrogated by prior acute rejection episodes. Remarkably, donor-specific hyporesponders had the better renal function and less chronic renal damage. Donor-specific hyporesponsiveness was inhibited by depleting CD4+ CD25(+high) T cells, which showed donor-Ag specificity. FOXP3+ CD4+ CD25(+high) Tregs both in peripheral blood and in renal infiltrates were higher in donor-specific hyporesponders than in nonhyporesponders, suggesting that the recruitment of Tregs in the allograft plays an important role for renal acceptance. In conclusion, reaching donor-specific hyporesponsiveness is feasible after renal transplantation and associated with Treg recruitment in the graft.

Low-dose cyclosporine with mycophenolate mofetil induces similar calcineurin activity and cytokine inhibition as does standard-dose cyclosporine in stable renal allografts.

One strategy to minimize nephrotoxicity in maintenance immunosuppression in renal transplantation is reduction of cyclosporine (CsA) with addition of mycophenolate mofetil (MMF). This approach seems safe, but concern exists about whether it yields adequate immunosuppression in the long term. Thus, we investigated the pharmacodynamic response to CsA in stable renal allografts treated with standard CsA (n = 17, CsA-C0h > or = 125 ng/mL) and low CsA plus MMF (n = 18 CsA-C0h <100 ng/mL). Patients treated with MMF without CsA (n = 13) and healthy subjects (n = 7) were used as controls. We observed that inhibition of calcineurin (CN) activity in peripheral blood mononuclear cells (PBMC), as well as interleukin (IL)-2 and interferon (IFN)-gamma production were similar in Standard-CsA and Low-CsA+MMF groups. Moreover, addition of MMF to a low CsA dose regime improved the correlation between CsA-C2h and both CN activity and IL-2 production. Thus, our results suggest that MMF could be synergistic with the pharmacodynamic effect of low CsA in maintenance immunosuppression.