D. R. Leary

NR1I2 polymorphisms are related to tacrolimus dose-adjusted exposure and BK viremia in adult kidney transplantation

Background Pregnane X, encoded by the gene NR112, is a nuclear receptor whose primary role is to promote the detoxification and clearance of drugs and other foreign compounds from the body. Aim The aim of this study was to analyze associations between NR1I2 polymorphisms, immunosuppressant drug exposure, and clinical outcomes in adult kidney transplant recipients. Methods Exposures to tacrolimus, mycophenolic acid, and total and free prednisolone were estimated at month 1 posttransplant using validated multiple regression-derived limited sampling strategies. Results In the 158 subjects studied, median (interquartile range) dose-adjusted exposure to tacrolimus was significantly higher in individuals carrying the NR1I2 8055T variant allele, when compared with exposure in wild-type individuals [20 (14, 22) &mgr;g·h/L/mg versus 15 (9, 24) &mgr;g·h/L/mg; P =0.0007]. Using multivariable logistic regression, NR1I2 8055T carrier status was independently predictive of higher dose-adjusted tacrolimus exposure (P=0.0005). Moreover, BK viremia was seen significantly more frequently in NR1I2 8055T allele carriers compared with wild-type individuals (38% vs 18%, P=0.005) and possession of the NR1I2 8055T allele imposed significantly higher odds of BK viremia (adjusted odds ratio, 2.76 [95% confidence interval, 1.33–7.73]; P=0.006). No significant difference in geometric mean peak BK viral replication titer was observed between 8055T carriers and noncarriers. No NR1I2 SNP or haplotype was significantly, independently associated with total or free prednisolone or MPA exposure. Conclusions These data demonstrate an impact of pregnane X receptor polymorphisms on tacrolimus pharmacokinetics. Association of the 8055T allele with BK viremia suggests clinically significant “overimmunosuppression” in individuals with this genotype.

Evaluation of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients

AIMS To examine the predictive performance of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients. METHODS Twenty full tacrolimus area under the concentration-time curve from 0 to 12 h post-dose (AUC(0-12)) profiles (AUCf) were collected from 20 subjects. Predicted tacrolimus AUC(0-12) (AUCp) was calculated using the following: (i) 42 multiple regression-derived limited sampling strategies (LSSs); (ii) five population pharmacokinetic (PK) models in the Bayesian forecasting program TCIWorks; and (iii) a Web-based consultancy service. Correlations (r(2)) between C(0) and AUCf and between AUCp and AUCf were examined. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated. RESULTS Correlation between C(0) and AUCf was 0.53. Using the 42 LSS equations, correlation between AUCp and AUCf ranged from 0.54 to 0.99. The MPPE and MAPE were <15% for 29 of 42 equations (62%), including five of eight equations based on sampling taken ≤2 h post-dose. Using the PK models in TCIWorks, AUCp derived from only C(0) values showed poor correlation with AUCf (r(2)=0.27-0.54) and unacceptable imprecision (MAPE 17.5-31.6%). In most cases, correlation, bias and imprecision estimates progressively improved with inclusion of a greater number of concentration time points. When concentration measurements at 0, 1, 2 and 4 h post-dose were applied, correlation between AUCp and AUCf ranged from 0.75 to 0.93, and MPPE and MAPE were <15% for all models examined. Using the Web-based consultancy service, correlation between AUCp and AUCf was 0.74, and MPPE and MAPE were 6.6 and 9.6%, respectively. CONCLUSIONS Limited sampling methods better predict tacrolimus exposure compared with C(0) measurement. Several LSSs based on sampling taken 2 h or less post-dose predicted exposure with acceptable bias and imprecision. Generally, Bayesian forecasting methods required inclusion of a concentration measurement from >2 h post-dose to adequately predict exposure.

Kidney transplant outcomes are related to tacrolimus, mycophenolic acid and prednisolone exposure in the first week.

This study analysed associations between tacrolimus, mycophenolic acid (MPA) and prednisolone exposures on day 4 and month 1 post kidney transplant and clinical outcomes. Area under the concentration‐time curve (AUC) for each drug was estimated using validated multiple regression‐derived limited sampling strategies. Multivariate logistic regression was used to associate drug exposure with clinical outcomes. One hundred and twenty subjects were studied. Between‐subject variability in dose‐adjusted exposure to each medication was high. Both day 4 tacrolimus and MPA exposures were independently predictive of delayed graft function (2.6 change in odds for a standard deviation (SD) increase in tacrolimus AUC0–12, P = 0.02; 0.23 change in odds for a SD increase in MPA AUC0–12, P = 0.02). Both day 4 MPA and total prednisolone exposures were independently predictive of rejection (0.20 change in odds for a SD increase in MPA AUC0–12, P = 0.04; 0.40 change in odds for a SD increase in total prednisolone AUC0–6, P = 0.03). Lowest tertile exposure to all three immunosuppressant medications imposed significantly higher odds of rejection [adjusted odds ratio 34.2 (95% CI 4.1, 284.4), P = 0.001]. This study highlights the importance of achieving early target exposure and suggests a potential role for individualized initial dosing or early therapeutic monitoring of all three immunosuppressive agents.

A randomized controlled trial of oral heme iron polypeptide versus oral iron supplementation for the treatment of anaemia in peritoneal dialysis patients: HEMATOCRIT trial

BACKGROUND Preliminary clinical evidence suggests that heme iron polypeptide (HIP) might represent a promising, novel oral iron supplementation strategy in chronic kidney disease. The aim of this multi-centre randomized controlled trial was to determine the ability of HIP administration to augment iron stores in darbepoetin (DPO)-treated patients compared with conventional oral iron supplementation. METHODS Adult peritoneal dialysis (PD) patients treated with DPO were randomized 1:1 to receive two capsules daily of either HIP or ferrous sulphate per os for 6 months. The primary outcome measure was transferrin saturation (TSAT). Secondary outcomes comprised serum ferritin, haemoglobin, DPO dose and responsiveness, and adverse events. RESULTS Sixty-two patients were randomized to HIP (n = 32) or ferrous sulphate (n = 30). On intention-to-treat analysis, the median (inter-quartile range) TSAT was 22% (16-29) in the HIP group compared with 20% (17-26) in controls (P = 0.65). HIP treatment was not significantly associated with TSAT at 6 months on multivariable analysis (P = 0.95). Similar results were found on per-protocol analysis and subgroup analysis in iron-deficient patients. Serum ferritin levels at 6 months were significantly lower in the HIP group (P = 0.003), while the cost of HIP was 7-fold higher than that of ferrous sulphate. No other differences in secondary outcomes were observed. CONCLUSIONS HIP showed no clear safety or efficacy benefit in PD patients compared with conventional oral iron supplements. The reduction in serum ferritin levels and high costs associated with HIP therapy suggest that this agent is unlikely to have a significant role in iron supplementation in PD patients.

A limited sampling strategy for the simultaneous estimation of tacrolimus, mycophenolic acid and unbound prednisolone exposure in adult kidney transplant recipients.

Aim:  The aim of this study was to develop a limited sampling strategy (LSS) for the simultaneous estimation of exposure to tacrolimus, mycophenolic acid and unbound prednisolone in adult kidney transplant recipients.

Evaluation of limited sampling strategies for total and free prednisolone in adult kidney transplant recipients

PurposeThe aims of this study were to evaluate the predictive performances of all previously derived limited sampling strategies (LSSs) for total prednisolone, and to derive LSSs for free prednisolone in an independent cohort of adult kidney transplant recipients.MethodsTotal and free prednisolone area under the concentration–time curve profiles from 0 to 12 hours post-dose (AUC0–12) were collected from 20 subjects. All previously published total prednisolone LSSs were identified from the literature. Free prednisolone LSSs were developed using multiple linear regression analyses. AUC predicted by each of the LSSs was compared with AUC0–12. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated to evaluate bias and imprecision.ResultsTotal dose-adjusted prednisolone exposure varied 5-fold among study participants, while free dose-adjusted prednisolone exposure varied 3-fold. Correlation (r2) between total and free prednisolone AUC0–12 was 0.79 (p = <0.0001) for the entire study cohort. This correlation was poorer in those early compared with late post-transplant (r2 = 0.42 (p = 0.04) versus r2 = 0.59 (p = 0.009) respectively). Ten previously published LSSs for total prednisolone and 15 derived LSSs for free prednisolone performed with acceptable levels of bias and imprecision (<15%). Of the free prednisolone LSSs, an equation incorporating 0.25-, 2- and 4-h concentrations showed the highest predictive power (AUC0–12 = −17.20 + 1.18 × C0.25 + 2.75 × C2 + 4.45 × C4; MPPE = 0.1%, MAPE = 4.6%).ConclusionsWide between-subject variability in drug exposure suggests a role for TDM. LSSs can accurately estimate both total and free prednisolone AUC0–12. However, given the poor correlation observed between the two parameters, our data suggest that free prednisolone LSSs may be preferable.

Detection of Recently Discovered Human Polyomaviruses in a Longitudinal Kidney Transplant Cohort

A large number of human polyomaviruses have been discovered in the last 7 years. However, little is known about the clinical impact on vulnerable immunosuppressed patient populations. Blood, urine, and respiratory swabs collected from a prospective, longitudinal adult kidney transplant cohort (n = 167) generally pre‐operatively, at day 4, months 1, 3, and 6 posttransplant, and at BK viremic episodes within the first year were screened for 12 human polyomaviruses using real‐time polymerase chain reaction. Newly discovered polyomaviruses were most commonly detected in the respiratory tract, with persistent shedding seen for up to 6 months posttransplant. Merkel cell polyomavirus was the most common detection, but was not associated with clinical symptoms or subsequent development of skin cancer or other skin abnormalities. In contrast, KI polyomavirus was associated with respiratory disease in a subset of patients. Human polyomavirus 9, Malawi polyomavirus, and human polyomavirus 12 were not detected in any patient samples.

Rationale and design of the oral HEMe iron polypeptide Against Treatment with Oral Controlled Release Iron Tablets trial for the correction of anaemia in peritoneal dialysis patients (HEMATOCRIT trial)

BackgroundThe main hypothesis of this study is that oral heme iron polypeptide (HIP; Proferrin® ES) administration will more effectively augment iron stores in erythropoietic stimulatory agent (ESA)-treated peritoneal dialysis (PD) patients than conventional oral iron supplementation (Ferrogradumet®).MethodsInclusion criteria are peritoneal dialysis patients treated with darbepoietin alpha (DPO; Aranesp®, Amgen) for ≥ 1 month. Patients will be randomized 1:1 to receive either slow-release ferrous sulphate (1 tablet twice daily; control) or HIP (1 tablet twice daily) for a period of 6 months. The study will follow an open-label design but outcome assessors will be blinded to study treatment. During the 6-month study period, haemoglobin levels will be measured monthly and iron studies (including transferring saturation [TSAT] measurements) will be performed bi-monthly. The primary outcome measure will be the difference in TSAT levels between the 2 groups at the end of the 6 month study period, adjusted for baseline values using analysis of covariance (ANCOVA). Secondary outcome measures will include serum ferritin concentration, haemoglobin level, DPO dosage, Keys index (DPO dosage divided by haemoglobin concentration), and occurrence of adverse events (especially gastrointestinal adverse events).DiscussionThis investigator-initiated multicentre study has been designed to provide evidence to help nephrologists and their peritoneal dialysis patients determine whether HIP administration more effectively augments iron stores in ESP-treated PD patients than conventional oral iron supplementation.Trial RegistrationAustralia New Zealand Clinical Trials Registry number ACTRN12609000432213.

EVALUATION OF LIMITED SAMPLING STRATEGIES FOR SIMULTANEOUS ESTIMATION OF TACROLIMUS, MYCOPHENOLIC ACID AND PREDNISOLONE EXPOSURE IN ADULT KIDNEY TRANSPLANT RECIPIENTS: 1613

K.A. Barraclough1, N.M. Isbel1, D.W. Johnson2, G. Medley3, K.J. Lee4, D. Leary5, S.B. Campbell1, C.E. Staatz6 1Nephrology, Princess Alexandra Hospital, Brisbane/AUSTRALIA, 2Department Of Nephrology, University of Queensland at Princess Alexandra Hospital, Brisbane/AUSTRALIA, 3Therapeutics Research Unit, University of Queensland, Brisbane/AUSTRALIA, 4Pharmacy, University of Queensland, Brisbane/AUSTRALIA, 5Nephrology, Princess Alexandra Hospital, Brisbane/QLD/AUSTRALIA, 6School Of Pharmacy, University of Queensland, Brisbane/Queensland/ AUSTRALIA