Influence of drug formulation on utilization and outcomes: Neoral and monitoring by sparse sample area under the curve

AUC-guided dosing of tacrolimus prevents progressive systemic overexposure in renal transplant recipients

BACKGROUND

Tacrolimus has a narrow therapeutic window, and bioavailability is known to vary considerably between renal transplant recipients. Most centers still rely on measurement of trough levels, but there are conflicting reports on the correlation between tacrolimus trough levels and systemic exposure, as measured by the area-under-the-concentration-over-time curve (AUC((0-12h))).

METHODS

We developed and validated a two-compartmental population-based pharmacokinetic model with Bayesian estimation of tacrolimus systemic exposure. Subsequently, we used this model to apply prospectively AUC-guided dosing of tacrolimus in 15 consecutive renal transplant recipients. The main objective was to study intrapatient variability in the course of time.

RESULTS

Bayesian forecasting with a two-point sampling strategy, a trough level, and a second sample obtained between two and four hours post-dose significantly improved the squared correlation with the AUC((0-12h)) (r(2)= 0.94). Compared with trough level monitoring only, this approach reduced the 95%-prediction interval by 50%. The Bayesian approach proved to be feasible in clinical practice, and provided accurate information about systemic tacrolimus exposure in individual patients. In the AUC-guided dosing cohort the apparent clearance of tacrolimus decreased gradually over time, which was not reflected in corresponding trough levels.

CONCLUSION

This simple, flexible method provides the opportunity to tailor immunosuppression, and should help minimize tacrolimus-related toxicity, such as nephrotoxicity and post-transplant diabetes mellitus.

Pharmacologic monitoring and outcomes of cyclosporine

Cyclosporine was introduced into clinical transplantation as an immunosuppressive agent 20 years ago. Cyclosporine is a critical dose drug with a narrow therapeutic index and requires monitoring through blood levels to avoid rejection through underexposure or toxicity through overexposure. Traditional monitoring was by measuring the trough level taken 12 hours after an oral dose, but the results correlated poorly with drug dose, toxicity, and outcome. Monitoring cyclosporine by calculating total drug exposure correlated better with outcome but was time consuming and labour intensive. An abbreviated measure of exposure over the first 4 hours after administration was found to predict outcome and allow dose adjustment. This was based on the observation that the majority of variability in the absorption of the drug was during the first 4 hours after administration--the absorption phase--and this was not reflected in the trough level. Cyclosporine exerts its immunosuppressive action by inhibition of calcineurin. The peak of this inhibition occurs during the peak concentration of the drug, which occurs during the absorption phase. On the basis of the fact that as a single time point the 2-hour level was the best surrogate marker of the maximum level, a strategy for monitoring by 2-hour levels (C2) evolved. It was shown in all organ types to be the best single point predictor of exposure and has led to an improvement in outcome both in de novo and in maintenance transplant patients.

The impact of cyclosporine on the development of immunosuppressive therapy—pediatric transplantation using cyclosporine

Cyclosporine A (CsA) was introduced to pediatric renal transplantation more than 20 years ago, and it has greatly improved graft survival and made transplantation the treatment of choice for children with end-stage renal failure. Exposure to CsA was shown to be highly variable among transplant recipients. Therefore, major efforts have been employed to monitor CsA blood levels. The widely used trough levels had never been formally validated, and every center had defined its own target values. With the advanced microemulsion formula of CsA, drug exposure became more predictable, but scientifically evaluated monitoring concepts are still lacking. Monitoring the absorption phase using single time points (eg, 2 hours after ingestion) is promising, as shown in adult trials. In pediatric transplant recipients, randomized clinical trials have to be implemented urgently to fully exploit the potential of CsA in the prevention of graft rejection while minimizing toxicity. Although newer immunosuppressive drugs have been developed, further studies should be undertaken to define the role of CsA in combination protocols.

Experience with conversion from sandimmun to neoral cyclosporine and the correlation of c2 levels with renal function

Pharmacologic monitoring of the cyclosporine microemulsion Neoral is an important tool to improve the efficacy and to avoid toxicity of the drug. Recent trials have shown that the absorption profiling tools represented by the area under the time-concentration curve from 0 to 4 hours postdose and concentration 2 hours postdose (C2) levels are the best predictors of acute rejection in the early posttransplant period. Since similar data regarding maintenance immunosuppression are scarce, we report our experience on Neoral C2 monitoring in renal transplant recipients during the late posttransplant period. However, available data on optimal Neoral C2 levels in the late posttransplantation period are scant and have not been correlated with well-defined endpoints such as chronic allograft nephropathy.

Spurious results in therapeutic drug monitoring research

Maximal correlation between measured blood concentration of a drug and an estimate of the area under the concentration-time curve (AUC) is widely used as criterion for the optimal blood sampling time-point in therapeutic drug monitoring (TDM) research. (More generally, the correlation between an estimate of AUC and a linear combination of several concentration measurements is considered, but the principles are the same.) This particular TDM research methodology is evaluated from a theoretical statistical perspective by considering a general nonspecific study. It is shown that the TDM research methodology produces spurious results because the optimal time-point is determined by irrelevant factors. Particularly, the sampling design is an important determinant. The sampling time-points are of course the only candidates for the optimal time-point, but they may also determine which candidate is optimal. In a special case, it is mathematically proven that any time-point except the first (trough level) can be made optimal by choosing the appropriate sampling design. This is probably true in all practical situations. The theoretical optimum is defined as the optimal time-point in the ideal theoretical sampling design where concentration measurements are made continuously in time. Hence, the theoretical optimum is independent of sampling designs, and the optimal time-point of a study is an approximation to the theoretical optimum. In a homogeneous study population, it can be proven, mathematically and under realistic assumptions, that the theoretical optimum is t(max). Particularly t(max), is the individual theoretical optimum. Heterogeneity of the study population can be an important determinant of the optimal time-point. In significantly heterogeneous study populations, the optimal time-point is usually extreme compared with the distribution of the individual optimal time-points in the population.

Cyclosporine microemulsion (Neoral) absorption profiling and sparse-sample predictors during the first 3 months after renal transplantation

Recent data suggest that optimal cyclosporine (CsA) exposure early post-transplant significantly reduces the risk of acute graft rejection. They indicate that trough level monitoring is inadequate for precise concentration-controlled therapy, and suggest that absorption profiling may offer a superior approach for guiding clinical immunosuppression with Neoral. An international, prospective, multicenter study examined the feasibility, accuracy, precision and clinical utility of cyclosporine microemulsion (Neoral) absorption profiling in de novo renal transplant recipients receiving basiliximab immunoprophylaxis and cyclosporine microemulsion maintenance immunosuppression. The nested pharmacokinetic study reported here was conducted in 4 study centers in which full (11-point) pharmacokinetic profiles were performed on days 3, 7, 14 and 84 post-transplant to examine absorption profile and absorption efficiency, and to determine optimal sparse-sampling pharmacokinetic methods to predict Neoral exposure. Twenty-four patients had complete 12-h pharmacokinetic (PK) data on all 4 sampling days. Area under the time-concentration curve (AUC) over the first 4 h of the 12-h dosage interval (AUC[0-4]) and AUC over the entire 12-h dosage interval (AUC[0-12]) reached 3803 +/- 1033 and 7462 +/- 2120 microg.h/L respectively, by day 3, remained stable throughout the first 2 weeks, and declined to 2310 +/- 698 and 4062 +/- 1158 microg.h/L by day 84 (p < 0.001). AUC[0-4], capturing the drug absorption phase, represented 52% of the AUC[0-12] values across the four PK study days (mean R2 > 0.90). Between-patient variability was highest for C0 and C1 (mean coefficient of variation [c.v.] 36-47%), and lower for C2 (mean c.v. 28%) and subsequent time-points during the dosing interval. Mean relative CsA absorption, measured by dose- and weight-adjusted AUC[0-4] and AUC[0-12], increased significantly over time. The dose- and weight-corrected AUC[0-4h] (DWC.AUC[0-4]) rose by over 100% (p < 0.001) from 753 +/- 202 at day 3 to 905 +/- 232 at day 7, 1080 +/- 330 at day 14 and 1521 +/- 316 by day 84, while the dose-and weight-corrected AUC[0-12h] (DWC.AUC[0-12]) rose by over 80% (p < 0.001) from 1477 +/- 390 microg.h/L/ mg/kg on day 3, to 1721 +/- 426 on day 7, 2086 +/- 478 on day 14 and 2690 +/- 602 on day 84 (p < 0.001). Relative CsA absorption varied over 5-fold between patients at day 3, but patients tended to remain within the same quartiles over time. Sparse-sample modeling identified optimum 3-point, 2-point and 1-point predictors for AUC[0-4] and AUC[0-12]. C2 was the most accurate and robust .1-point predictor for AUC[0-4] (mean R2: 0.80), while C3 was superior for AUC[0-12] (mean R2: 0.75). C0 was not a good predictor of either AUC[0-4] or AUC[0-12] (mean R2: 0.13 and 0.24, respectively).

CONCLUSION

Absorption profiling defines the heterogeneity in CsA exposure and relative absorption post-transplant. A 2-h post-dose blood sample is the most consistent, accurate and robust single-point predictor of the absorption phase measured by AUC[0-4] and should replace trough level monitoring for accurate concentration-control of Neoral therapy in the clinical setting. The use of additional samples at 1 and 3h is more complex and costly, but increases prediction accuracy and may be valuable in selected patients with erratic absorption.

Absorption profiling of cyclosporine microemulsion (neoral) during the first 2 weeks after renal transplantation

BACKGROUND

Evidence suggests that optimal immunosuppressive drug exposure must be achieved early posttransplant to minimize the risk of acute graft rejection. This study was designed to examine the absorption profile of Neoral during the first 2 weeks after renal transplantation, to develop simple sparse-sampling pharmacokinetic methods to predict exposure, and to explore the target range for optimal clinical immunosuppression under conditions of normal clinical practice.

METHODS

The prospective multicenter study was conducted in six Canadian renal transplant centers in patients receiving Neoral-based immunosuppression. Full (8-point) pharmacokinetic studies were performed on days 3, 7, and 14 posttransplant in a nested subset of patients, and the occurrence and severity of acute rejection, infection or other adverse effects, routine laboratory parameters, and vital signs were assessed on days 3, 7, 14, and 28.

RESULTS

A total of 38 adult kidney graft recipients were studied, of whom a nested subset of 16 patients had complete 12-hr pharmacokinetic (PK) data on all 3 sampling days. Mean area under the time-concentration curve over the entire 12-hr dosage interval (AUC[0-12]) was 9249+/-3236 microg.hr/L by day 3 and did not change significantly throughout the study, although dose-corrected AUC[0-12] rose by 20% from 1924+/-671 microg.hr/L on day 3 to 2316+/-697 microg.hr/L on day 14 (P=0.067). Mean AUC[0-4] was 4566+/-1463 microg.hr/L by day 3 and also did not change significantly, although the dose-adjusted AUC[0-4] rose by 31% from 952+/-317 microg.hr/L on day 3 to 1250+/-697 microg.hr/L on day 14 (P=0.009). AUC[0-4] represented 52% of the AUC[0-12] values across the three PK study days and closely predicted this latter value (R2=0.803 day 3, R2=0.972 day 14). Cyclosporine (CsA) concentration profiles became more uniform throughout the first 14 days posttransplant, with a reduction in Tmax from 2.45 to 1.48 hr (P<0.005) and a significant decrease in coefficient of variation for AUC[0-12] (35% vs. 21%, P<0.005) and for Tmax (47.4% vs. 33.1%, P<0.005). Predosage trough level (C0) was a poor predictor of drug exposure, with R2 values less than 0.5 for AUC[0-4] and 0.7 for AUC[0-12] at all time points. Sparse sample modeling identified three 3-point sparse-sampling strategies that predicted AUC[0-12] and AUC[0-4] with R2 values approaching or exceeding 0.9 on all three study days; C2 or C3 seemed to be the most important single predictor, with R2 values > 0.80. Ten of the 36 treated patients (27.8%) experienced 13 episodes of acute rejection by 28 days posttransplant. Longitudinal logistic regression showed no association between C0 and rejection, but lower AUC[0-12] values were marginally (P=0.099) and lower AUC[0-4] values were significantly (P=0.046) associated with increased risk of rejection. CsA exposure on day 7 (n=29) was significantly lower in patients who experienced acute rejection in the second week than in those who were rejection free whether measured by AUC[0-12] (7976+/-1476 vs. 10,239+/-2759 microg.hr/L; P=0.048), AUC[0-4] (4027+/-412 vs. 5623+/-1389 microg.hr/L; P<0.0001), C2 (1116+/-183 vs. 1852+/-522 microg/L; P<0.0001), or Cmax (1415+/-323 vs. 2084+/-450 microg/L; P=0.005), and rejection was significantly less common in patients with an AUC[0-4]> 4,500 microg.hr/L (7% vs. 40%; P=0.041) or a C2 level>1500 microg/L (0% vs. 58%; P<0.001) on day 7 (sensitivity, 100%; specificity, 75%; positive predictive value, 58%; negative predictive value, 100%). There was no evident relationship between CsA exposure and renal toxicity within this patient sample.

CONCLUSIONS

Absorption of CsA is highly heterogeneous immediately posttransplant, although the pharmacokinetic profile normalizes, interpatient variability decreases, and CsA absorption increases throughout the first 2 weeks permitting a reduction in Neoral dose to achieve constant exposure. Trough (C0) levels do not accurately predict CsA exposure or rejection risk and should be replaced by sparse or single point (C2) sampling methods, which offer a high predictive value to optimize the use of this drug and reduce rejection risk. Acute rejection is significantly more common with low CsA exposure during the first week posttransplant, and levels above the threshold of approximately AUC[0-4] 4500 microg.hr/L or C2 1500 microg/L are desirable to minimize the risk of rejection.

Neoral use in the renal transplant recipient

This review and critical analysis of current trends of immunosuppression management in pediatric transplantation provides evidence and support for the continued role of Neoral as an indispensable part of immunosuppressive protocols. CyA formulation influences clinical outcomes such as acute rejection, as confirmed by several multicenter studies. The CyA microemulsion formulation reduces pharmacokinetic variability and its consequent impact on outcomes over the long term. An advanced TDM strategy can improve the effectiveness and safety of immunosuppression in both de novo and maintenance renal transplant patients. There are potential risks resulting from CyA withdrawal strategies. Neoral is an indispensable part of combination protocols in renal transplantation.