Cyclosporine monitoring in patients with renal transplants: two- or three-point methods that estimate area under the curve are superior to trough levels in predicting drug exposure

The pig as a preclinical model for predicting oral bioavailability and in vivo performance of pharmaceutical oral dosage forms: a PEARRL review

OBJECTIVES

In pharmaceutical drug development, preclinical tests in animal models are essential to demonstrate whether the new drug is orally bioavailable and to gain a first insight into in vivo pharmacokinetic parameters that can subsequently be used to predict human values. Despite significant advances in the development of bio-predictive in vitro models and increasing ethical expectations for reducing the number of animals used for research purposes, there is still a need for appropriately selected pre-clinical in vivo testing to provide guidance on the decision to progress to testing in humans. The selection of the appropriate animal models is essential both to maximise the learning that can be obtained from such experiments and to avoid unnecessary testing in a range of species.

KEY FINDINGS

The present review, provides an insight into the suitability of the pig model for predicting oral bioavailability in humans, by comparing the conditions in the GIT. It also contains a comparison between the bioavailability of compounds dosed to both humans and pigs, to provide an insight into the relative correlation and examples on why a lack of correlation may be observed.

SUMMARY

While there is a general trend towards predicting human bioavailability from pig data, there is considerable variability in the data set, most likely reflecting species specific differences in individual drug metabolism. Nonetheless, the correlation between pigs vs. humans was comparable to that reported for dogs vs. humans. The presented data demonstrate the suitability of the pig as a preclinical model to predict bioavailability in human.

Validation of sparse sampling strategies to estimate cyclosporine A area under the concentration-time curve using either a specific radioimmunoassay or high-performance liquid chromatography method

INTRODUCTION

Area under the concentration-time curve (AUC) has been advocated as a better parameter to monitor cyclosporine A than trough concentrations. Up to now, more than 100 equations to estimate AUC using a limited sampling strategy have been published, but not all have been validated.

MATERIAL AND METHODS

Eight equations for AUC0-12h and two for AUC0-8h were validated. Concentrations of cyclosporine A were analyzed by high-performance liquid chromatography (HPLC) and a specific radioimmunoassay (RIA) method. Forty male renal transplant patients were included in the study. Blood samples were taken predose and at 0.5, 1, 1.5, 2, 3, 5, 8, and 12 hours after the morning dose when the patient was in steady state. The percentage prediction error (%pe) was used for an assessment of the performance of the equations. Mean %pe less than ± 15% and absolute %pe less than 30% in 95% of predictions were considered to be acceptable. Other possibilities such as %pe less than 25%, 20%, and 15% were also tested.

RESULTS

Eight equations for AUC0-12h met the requirements using both assays, six in the HPLC set only and four in the RIA set only. The highest precision was obtained with AUC0-12h = 123.792 + 1.165*C1h + 3.021*C3h + 7.33*C8h proposed by de Mattos et al. The mean %pe was 1% ± 8% (-16 to 19) for HPLC (values given as mean ± standard deviation [range]) and -1 ± 5 (-17 to 10) for RIA. Mean absolute %pe was 7 ± 5 (0.0 to 19) for HPLC and 4 ± 4 (0.0 to 17) for RIA. For clinical use, the most suitable equation was AUC0-12h = 363.078 + 8.77*C1h + 3.07*C3h proposed by Wacke et al, which produced the second lowest %pe and used two sampling points in the period of 1 to 3 hours after dose. The mean %pe was -7 ± 10 (-25 to 25) for HPLC and 2.3 ± 6 (-10 to 17) for RIA. Mean absolute %pe was 10 ± 7 (0.4 to 25) for HPLC and 5 ± 4 (0.0 to 17) for RIA. The equation: AUC0-8h = 55.37 + 2.89*C0h + 1.08*C1h0.9*C2h + 2.23*C3h proposed by Foradori et al met the criteria with 95% of prediction with absolute %pe less than 15% in the HPLC set and 10% in the RIA set.

CONCLUSION

The validation of equations is of major importance for prediction precision, whereas the analytical method for limited sampling strategy proposals had no influence. Because of the wide interassay variability, it is also important to know which analytical method was used for AUC calculation when interpreting the results.

Novel strategies for immune monitoring in kidney transplant recipients

The ongoing quandary in kidney transplantation is discovering methods to prolong graft survival. To achieve this, there is a search for optimal methods to use immunosuppressive therapy, where rejection and chronic graft damage is minimized without causing an increased risk of infections, malignancy, or toxicities. The purpose of this review was to discuss the limitations of current immunosuppressant drug monitoring as well as the clinical application of novel methods of monitoring both immunosuppressants and the immune reaction within the allograft.

Early phase limited sampling strategy characterizing tacrolimus and mycophenolic acid pharmacokinetics adapted to the maintenance phase of renal transplant patients

The aim of this study was to examine whether a limited sampling strategy (LSS) to allow the simultaneous estimation of the area under the concentration-time curves (AUCs) of tacrolimus and mycophenolic acid (MPA) calculated in the early stage after renal transplantation could be applied to maintenance phase pharmacokinetics. Seventy Japanese patients were enrolled. One year after transplantation, samples were collected just before and 1, 2, 3, 4, 6, 9, and 12 hours after tacrolimus and mycophenolate mofetil administration at 9:00 am and at 9:00 pm. The prediction formulas on day 28 (tacrolimus AUC 0-12 = 7.04 x C 0h + 1.71 x C 2h + 3.23 x C 4h + 15.19 and 2.25 x C 2h + 1.92 x C 4h + 7.27 x C 9h + 6.61, and MPA AUC 0-12 = 0.26 x C 0h + 2.06 x C 2h + 3.82 x C 4h + 20.38 and 1.77 x C 2h + 2.34 x C 4h + 4.76 x C 9h + 15.94) were applied to pharmacokinetic data obtained at 1 year. Three error indices [percent mean prediction error (ME), % mean absolute error, and percent root mean squared prediction error (RMSE)] were used to evaluate the predictive bias, accuracy, and precision. The predicted AUC 0-12 of tacrolimus and MPA at 3 time points, C 2h-C 4h-C 9h, showed higher correlation with the measured AUC 0-12 of tacrolimus and MPA (r2 = 0.817 and 0.789, respectively) in comparison with those at C 0h-C 2h-C 4h. The values for the prediction formulas for tacrolimus AUC at 1 year using the C 2h-C 4h-C 9h combination yielded less than 5% for %ME and 15% for %RMSE. The %ME and %RMSE values of the prediction formulas for tacrolimus AUC using the C 0h-C 2h-C 4h combination were 6.3% and 15.9%, respectively. The %ME and %RMSE values of the prediction formulas for MPA AUC at 1 year using the C 0h-C 2h-C 4h combination were 5.9% and 25.8%, respectively, and those for the C 2h-C 4h-C 9h combination were 4.9% and 21.2%, respectively. AUC 6-12/AUC 0-12 of MPA 1 year after transplantation was significantly lower than 28 days after transplantation. An LSS using C 2h-C 4h-C 9h seems to be applicable for predicting the AUC of tacrolimus and MPA at either posttransplantation stage. The enterohepatic circulation of MPA was significantly reduced 1 year after transplantation. Therefore, 1 year after transplantation, the estimation of the AUC 0-12 of MPA for the C 0h-C 2h-C 4h equations was imprecise. It is important that the LSS includes C 9h because it contains information on the secondary plasma peak of MPA.

Limited sampling strategy for simultaneous estimation of the area under the concentration-time curve of tacrolimus and mycophenolic acid in adult renal transplant recipients

The aim of this study was to develop a limited sampling strategy to allow the simultaneous estimation of the area under the concentration-time curves (AUCs) of tacrolimus and mycophenolic acid (MPA), the active metabolite of the prodrug mycophenolate mofetil, using a small number of samples from patients undergoing renal transplantation. Fifty Japanese patients were enrolled. On day 28 after transplantation, samples were collected just before and 1, 2, 3, 4, 6, 9, and 12 hours after tacrolimus and mycophenolate mofetil administration at 9:00 am and 9:00 pm. The full pharmacokinetic profiles obtained from these timed concentration data were used to choose the best sampling times. Three error indices (percent mean error, percent mean absolute error, and percent relative mean square error) were used to evaluate the predictive bias, accuracy, and precision. The predicted AUC0-12 of MPA calculated at the three time points of C2h-C4h-C9h best approximated the actual AUC0-12 of MPA (r = 0.877), and the AUC0-12 of tacrolimus calculated at the same time points predicted a good correlation with the actual AUC (r = 0.928). When the three sampling times of trough level (C0h) and two other points within 4 hours after administration were used, the three points of C0h-C2h-C4h were the best points for estimation of the AUC0-12 tacrolimus and MPA (AUC0-12 = 7.04.C0 + 1.71.C2 + 3.23.C4 + 15.19, r = 0.799, P < 0.001 and AUC0-12 = 0.26.C0 + 2.06.C2 + 3.82.C4 + 20.38, r = 0.693, P < 0.001, respectively). The percent mean error, percent mean absolute error, and percent relative mean square error of the prediction formula using the three time points of C0h-C2h-C4h were -0.3%, 8.8%, and 13.5% for tacrolimus and 2.9%, 17.1%, and 21.5% for MPA, respectively. A limited sampling strategy using C2h-C4h-C9h provides the most reliable and accurate simultaneous estimation of the AUC0-12 of tacrolimus and MPA in patients undergoing renal transplantation. In addition, a limited sampling strategy using C0h-C2h-C4h is recommended for the simultaneous estimation of the AUC0-12 of tacrolimus and MPA when focused on samples collected within 4 hours after administration for clinical expediency.

Single time point measurement by C2 or C3 is highly predictive in cyclosporine area under the curve estimation immediately after lung transplantation

BACKGROUND

The two h post-dose cyclosporine (CsA) concentration has been advocated as the optimal time point measurement for CsA area under the curve (AUC) estimation after solid organ transplantation. The aim of the study was to investigate whether intensified CsA monitoring is necessary, or if a single time point measurement is accurate to estimate the AUC in the very early period following lung transplantation (LuTX).

METHODS

Within the first two wk following transplantation, daily AUCs were calculated by serial CsA measurements at zero, one, two, three, four, and six h (C0-C6) in 12 consecutive lung transplant recipients. Correlation of single CsA measurements and AUC as well as linear regression analysis was performed to evaluate the most predictive single CsA blood level regarding the AUC.

RESULTS

A total of 606 CsA concentration measurements were performed and the 101 corresponding AUCs were calculated for each patient. Mean AUC was 3443 +/- 1451 microg/L. C0: 361 +/- 118 microg/L, C1: 481 +/- 231 microg/L, C2: 682 +/- 314 microg/L, C3: 715 +/- 347 microg/L, C4: 658 +/- 271 microg/L, C6: 571 +/- 260 microg/L. The correlation of CsA serum levels with AUC was the lowest at trough levels (C0) with a correlation coefficient (r = 0.31) and highest at three h (C3: r = 0.89) and two h (C2: r = 0.88).

CONCLUSIONS

Similar to a stable post-transplant period, CsA trough levels turned out to have poor correlation with the corresponding AUC early after LuTX. The highest correlation of C3 with the AUC may be explained by delayed intestinal resorption immediately post-operative, however C2 is a peer parameter. Optimum AUCs and corresponding C2 or C3 levels in the immediate post-operative phase however remain to be determined.

Monitoring of blood cyclosporine concentration in steroid-resistant nephrotic syndrome

OBJECTIVE

Cyclosporine has been used for patients with nephrotic syndrome. Because of substantial inter- and intra-patient variability and a narrow therapeutic window, drug monitoring of cyclosporine is mandatory. To confirm the therapeutic effects of a cyclosporine microemulsion (CSAME), the absorption profile of the agent after preprandial administration was determined in steroid-resistant patients with refractory nephrotic syndrome.

METHODS

Fourteen patients were enrolled into the study (mean age, 31.2+/-12; 6 men, 8 women). The patients received 1.5 mg/kg of cyclosporine 30 minutes before breakfast for 6 months. Blood cyclosporine concentration was measured 5 times serially: before administration (C0) and at 1-hour intervals until 4 hours after administration of cyclosporine (C1-C4). In addition, area under the concentration-time curve from 0-4 hours (AUC0-4) was calculated.

RESULTS

After 6 months, CSAME showed marked improvement in proteinuria levels (8.3+/-4.8 g/day vs 0.8+/-0.4 g/day, p<0.001). No changes in serum creatinine and urea nitrogen levels were observed. In 83% of the patients, the CSAME peak concentration appeared within 1 hour after administration (C1). A strong positive correlation was noted between AUC0-4 and C1 (R2=0.90312) and C2 (R2=0.78431). The mean steroid (prednisolone) dose was 40 mg/day when CSAME treatment was started, but a lowering of the dose to 17.5 mg/day (p<0.001) was achieved at 6 months after CSAME therapy.

CONCLUSION

Preprandial administration of CSAME is effective in steroid-resistant patients with refractory nephrotic syndrome. C1 or C2, but not C0, was a good clinical marker for CSAME exposure.

Calcineurin inhibitors in pediatric renal transplant recipients

The calcineurin inhibitors, cyclosporine (ciclosporin) [microemulsion] and tacrolimus, are the principal immunosuppressants prescribed for adult and pediatric renal transplantation. For pediatric patients, both drugs should be dosed per body surface area, and pharmacokinetic monitoring is mandatory. While monitoring of the trough levels may suffice for tacrolimus, cyclosporine therapy that utilizes the microemulsion formulation requires additional monitoring (e.g. determination of 2-hour post-dose levels). In a well designed randomized study in children, as in studies in adults, there was no difference in short-term patient and graft survival with cyclosporine microemulsion and tacrolimus. However, tacrolimus was significantly more effective than cyclosporine microemulsion in preventing acute rejection after renal transplantation when used in conjunction with azathioprine and corticosteroids. With regard to long-term outcome, the difference in acute rejection episodes resulted in a better glomerular filtration rate at 1 year after transplantation and eventually in better graft survival 4 years after renal transplantation. Whether this difference persists when calcineurin inhibitors are used in combination with mycophenolate mofetil has not been determined. The prevalence of hypomagnesemia was higher in the tacrolimus group whereas hypertrichosis and gingival hyperplasia occurred more frequently in the cyclosporine group. In contrast with adults, the incidence of post-transplantation diabetes mellitus was not significantly different between tacrolimus- and cyclosporine-treated patients. There was also no difference with regard to post-transplantation lymphoproliferative disorder. Medication costs were similar, but in view of the lower rejection episodes and better long-term graft survival as well as the more favorable cosmetic side effect profile, tacrolimus may be preferable. The recommendation drawn from the available data is that both cyclosporine and tacrolimus can be used safely and effectively in children. We recommend that cyclosporine should be chosen when patients experience tacrolimus-related adverse events.

Influence of different allelic variants of the CYP3A and ABCB1 genes on the tacrolimus pharmacokinetic profile of Chinese renal transplant recipients

Tacrolimus has a narrow therapeutic window and a wide interindividual variation in its pharmacokinetics. The cytochrome P450 3A (CYP3A) and the ATP-binding cassette B1 (ABCB1) genes play an important role in the tacrolimus disposition. Therefore, the aim of this study was to evaluate whether CYP3A and ABCB1 polymorphisms are associated with the area under the time concentration curve (AUC0-12) calculated using a two time point sample strategy. The CYP3A and ABCB1 genotypes were determined by real-time polymerase chain reaction (RT-PCR) fluorescence resonance energy transfer (FRET) assays in 103 Chinese renal transplant recipients and consequently related to their dose-normalized (dn)AUC0-12. A significant allele-dependent effect (Kruskal-Wallis; p < 0.001) was observed between the CYP3A5*3 polymorphism and the dnAUC0-12. Multiple regression analysis showed that the CYP3A5*3 polymorphism is the most significant independent variable and explained 35% of the dose requirement variability in relation to tacrolimus use. Regarding the ABCB1 G2677T/A and C3435T polymorphisms, a trend was observed between the different genotypes and the dnAUC0-12. In conclusion, the CYP3A5*3 polymorphism may be an important factor in determining the dose requirement for tacrolimus and genotyping can help determine the initial daily dose required by individual patients for adequate immunosuppression.

Pharmacokinetic profiling of cyclosporine microemulsion during the first 3 weeks after simultaneous pancreas-kidney transplantation

The optimal effect of therapy with cyclosporine (CsA) seeks to minimize undesirable side effects while maximizing immunosuppression. This balance, depends on CsA exposure, which may be characterized by the area under the concentration-time-curve (AUC). Therefore, we tested the pharmacokinetic profile of microemulsion CsA as a superior approach to guide clinical immunosuppression after de novo simultaneous pancreas-kidney transplantations. We examined 10 consecutive pancreas-kidney recipients with type 1 diabetes and end-stage renal disease. All patients were treated with a regimen consisting of CsA, mycophenolate mofetil (MMF), and prednisone. Full (9-point) pharmacokinetic studies (C0, C1, C2, C3, C4, C6, C8, C10, C12) were performed on week 1 and during week 3 to examine CsA pharmacokinetic profiles. Mean AUC0-12 of 4431 +/- 2400 microg x h/L at week 1 remained stable at week 3 (5119 +/- 1190 microg x h/L). The C6 sampling time displayed the best correlation with AUC0-12 (r2 = 0.881), followed by C3 (r2 = 0.758). Our preliminary data after simultaneous pancreas-kidney transplantation support the hypothesis that C3 or C6 sampling is a more accurate predictor of the AUC0-12 than C0. The combination of two samplings, namely C3 + C6 (r2 = 0.938) or C2 + C6 (r2 = 0.955) proved excellent prediction of exposure after simultaneous pancreas-kidney transplantation.

Untreated rejection in 6-month protocol biopsies is not associated with fibrosis in serial biopsies or with loss of graft function

Donor age, calcineurin inhibitor nephrotoxicity, and acute rejection are the most significant predictors of chronic allograft nephropathy. Protocol biopsies, both in deceased- and living-donor renal grafts, have shown that cortical tubulointerstitial fibrosis correlates with graft survival and function. The impact of not treating subclinical acute rejection (SAR) is less clear. In this study, 126 de novo renal transplant recipients were randomly assigned to receive area-under-the-curve-controlled exposure of either a cyclosporine or a tacrolimus-based immunosuppressive regimen that included steroids, mycophenolate mofetil, and basiliximab induction. Protocol biopsies were taken before and 6 and 12 mo after transplantation. The prevalence of SAR was determined retrospectively. Fibrosis was evaluated by quantitative digital analysis of Sirius red staining in serial biopsies. Donor age correlated significantly with tubulointerstitial fibrosis in pretransplantation biopsies and inferior graft function at month 6 (rtau = -0.26; P = 0.033). Acute rejection incidence was 11.5%, and no clinical late rejection occurred. The prevalence of SAR at 6 mo was 30.8% but was not associated with differences in serial quantitative Sirius red staining at 6 or 12 mo, proteinuria, or progressive loss of GFR up to 2 yr. No differences were found in donor variables, histocompatibility, rejection history, or exposure of immunosuppressants. Controlled individualized calcineurin inhibitor exposure and subsequent tapering resulted in a low early acute rejection rate and prevented late acute rejection. Because, by design, we did not treat SAR, these results provide evidence that asymptomatic infiltrates in 6-mo surveillance biopsies may not be deleterious in the intermediate term. There is need for reliable biomarkers to prove that not all cell infiltrates are equivalent or that infiltrates may change with time.

The nucleotide derivatives inosine and inosinic acid inhibit intestinal absorption of mizoribine in rats

Inosine is absorbed via a N1 transporter that is selective for purine nucleosides. It is conceivable that inosine and inosinic acid might affect the intestinal absorption of mizoribine, an imidazole nucleoside that inhibits the de novo production pathway of guanine ribonucleotide. An in situ loop experiment was performed using four intestinal loop segments prepared by ligation: segment 1, about 6 to 9 cm from the end of the pylorus; segment 2, about 10 to 13 cm; segment 3, about 14 to 17 cm; and segment 4, about 18 to 21 cm. Mizoribine (0.1 mg/ml) or mizoribine+inosine (1 or 10 mg/ml) were infused into each loop. The absorption rate in the most proximal segment of intestinal loop was the highest. In the presence of inosine, this rate decreased significantly. Urinary recovery rates of mizoribine were significantly decreased by pretreatment with inosine or inosinic acid. The Cmax in the group given mizoribine+inosinic acid was significantly lower than that in the group given mizoribine alone. These results strongly indicate that (I) the N1 transporter in the intestine might act to absorb mizoribine; and (II) inosine and inosinic acid might competitively inhibit the absorption of mizoribine via the N1 transporter.

No difference in degree of interstitial Sirius red-stained area in serial biopsies from area under concentration-over-time curves-guided cyclosporine versus tacrolimus-treated renal transplant recipients at one year

Interstitial fibrosis is the main characteristic of chronic allograft nephropathy and long-term graft failure. Cyclosporin (CsA) is thought to be more fibrogenic than tacrolimus. In a prospective, randomized, multicenter trial using a calcineurin-sparing regimen, renal interstitial volume was compared in CsA- and tacrolimus-treated renal transplant recipients by image analysis of Sirius red (SR)-stained cortical areas in protocol biopsies obtained at 6 mo (n = 94) and 12 mo (n = 97) after transplantation. Immunosuppression consisted of CsA or tacrolimus, CD25 mAb, mycophenolate mofetil, and prednisolone. CsA therapy increased the 6-mo risk for subclinical rejection. The prevalence of subclinical rejection was 38.8% in the CsA-treated and 15.2% in the tacrolimus-treated patient group (P = 0.012). Strikingly, no difference in the degree of interstitial SR-stained area was detectable between the two treatment groups. In particular, previous subclinical rejection episodes did not influence the degree of interstitial volume. Also, no difference in GFR occurred at 1 yr, when the mean GFR mounted 63 ml/min. No significant differences in the degree of interstitial SR-stained area could be observed at 6 and 12 mo between CsA- and tacrolimus-treated renal transplant recipients. Although CsA-treated patients developed significantly more subclinical rejections at 6 mo, this did not influence the degree of SR staining or the change in renal function at 1 yr.

Limited sampling strategy for cyclosporine (Neoral) area under the curve monitoring in pediatric kidney transplant recipients

Cyclosporine (CSA; Neoral) is one of the most common immunosuppressants used in pediatric renal transplantation. Research in adult renal transplant recipients has shown that 2-h post-dose concentration (C2) monitoring and limited sampling strategies (LSSs) are better at predicting drug exposure and outcome than trough concentrations (C0). While C0 monitoring is the usual practice in pediatric renal transplant patients, area under the curve (AUC) monitoring has been shown to be superior in terms of predictive ability and outcomes. However, AUC monitoring is impractical and inconvenient in a clinic setting because it involves many blood samples. An LSS provides a reliable alternative. The purpose of this study was to prospectively define an LSS (AUC(0-12)) for CSA monitoring and to test its predictive performance. As well, an LSS (AUC(0-4)) for CSA was developed and its predictive performance tested. Blood samples for CSA concentrations were collected in 29 stable pediatric renal transplant patients prior to (t = 0) and at 0.5, 1, 2, 4, 6, and 8 h following a steady-state morning CSA dose. AUC was calculated by the trapezoidal method; LSSs for AUC(0-12) and AUC(0-4) were determined using multiple regression analysis in 14 patients; and the LSSs' predictive performance was tested in 15 additional patients. Both LSSs require two blood samples. For the LSS (AUC(0-12)), blood samples are required immediately before the dose and 2 h post-dose: AUC(0-12) = 12.45 C0 + 2.17 C2 + 723.16 (r2 = 0.909). For the LSS (AUC(0-4)), blood samples are required at one and 2 h post-dose, AUC(0-4) = 1.17 C1 + 1.85 C2 - 41.00 (r2 = 0.971). The LSSs demonstrated low bias and high precision for both AUC(0-12) and AUC(0-4). Our two-concentration LSSs are accurate and precise predictors that are more clinically useful for our patient population than other LSSs that have been developed for pediatric renal transplant patients. Our study template provides a guide for other centers to develop accurate and precise LSSs specific to their own patient population.

Monitoring of Cyclosporine 2-Hour Post-Dose Levels in Heart Transplantation: Improvement in Clinical Outcomes

BACKGROUND

Cyclosporine 2-hour post-dose (C2) monitoring is predictive of outcomes in solid-organ transplants. The purpose of this study was to determine C2 levels at various time points after heart transplantation and determine whether trough (C0) or C2 better predicts clinical outcomes.

METHODS

This was a 2-phase prospective study with paired determinations of cyclosporine levels at C0 and C2 in 58 heart transplant patients (46 men; mean age, 56 years). Phase I (6-month follow-up): cyclosporine monitored according to C0 levels (C2 blinded). Phase II (6-month follow-up): cyclosporine monitored according to C2 levels (C0 blinded). Clinical outcomes assessed were severe infections, rejection score, and renal dysfunction.

RESULTS

No differences were observed in renal function between the phases. In Phase I, 8 infections (4 severe) and in Phase II, 6 infections (2 severe) were detected. During Phase I, the C0 levels did not correlate (p = .96) with the presence (195 +/- 121 ng/ml) or not (197 +/- 100 ng/ml) of rejection. During Phase II, C0 levels did not correlate (p = .88) with the presence (204 +/- 85 ng/ml) or not (209 +/- 138 ng/ml) of rejection. During Phase I, C2 levels did correlate (p = 0.022) with the presence (777 +/- 326 ng/ml) or not (1,015 +/- 422 ng/ml) of rejection. During Phase II, higher C2 levels showed a significant correlation (p = 0.03) with no rejection (967 +/- 470 ng/ml vs 765 +/- 297 ng/ml, no rejection vs rejection, respectively).

CONCLUSION

High C2 levels were associated with less episodes of acute cellular rejection in patients post-heart transplantation. Monitoring with C2 levels is feasible and safe in terms of preservation of renal function and infection rates.

Evaluation of a Limited Sampling Strategy to Estimate Area Under the Curve of Tacrolimus in Adult Renal Transplant Patients

Limited sampling strategies have been developed to predict full AUCs. The goal of this study was to develop a limited sampling strategy to estimate the AUC of tacrolimus in adult renal transplant patients and to evaluate its predictive performance in an independent patient population. A total of 27 tacrolimus pharmacokinetic profiles were studied. Blood samples were collected before the dose (0) and at 0.5, 1, 2, 4, 6, 8, and 12 hours postdose. The study was divided into 2 phases. In phase 1, the goal was to obtain a sampling strategy from 14 pharmacokinetic profiles. In phase 2, the bias and precision of the model were evaluated in another 13 pharmacokinetic profiles. The best correlation was achieved at 4 hours after dose (r(2) = 0.790). Stepwise multiple regression analysis determined that the abbreviated AUC at 0, 1, and 4 hours could accurately predict total AUC (r(2) = 0.965). The following formula was developed: AUC = 8.90 + 4.0C0h+ 1.77C1h + 5.47C4h. No significant differences were found between calculated and estimated AUC (165.6 +/- 41.1 and 166.7 +/- 43.2 ng.h/mL, respectively). The mean prediction error (MPE), the relative prediction error (PE), and the mean squared error (MSE) were 0.48 ng.h/mL, 0.16%, and 40.0 ng.h/mL, respectively. The limited sampling with use of the 3 levels at 0, 1, and 4 hours postdose provides accurate, reliable determination of tacrolimus AUC in renal transplant patients.

Cyclosporine Monitoring With 2-Hour Postdose Levels in Heart Transplant Recipients

Cyclosporine therapeutic drug monitoring based on 2-hour postdose concentration (C2) compared with conventional trough concentration (C0) can improve clinical outcomes for de novo renal and liver transplant patients. However, in heart transplant patients, published studies are limited. To determine the clinical significance of C2 compared with C0 following orthotopic heart transplantation, the authors measured CsA at C0 and C2 and estimated CsA area under the curve (AUC) using Bayesian estimation and 4 sparse sample algorithms in a cross section of 31 adult patients receiving triple-drug immunosuppression with CsA, mycophenolate mofetil (MMF), and prednisone. CsA was measured using a validated HPLC method. Endomyocardial biopsies were graded based on the ISHLT system. Mean +/- SD values for CsA dose, C0, and C2 were 4.8 +/- 1.4 mg/kg/d, 240 +/- 62 microg/L, and 1319 +/- 469 microg/L, respectively. Correlation with AUC, using different estimation algorithms, was better for C2 (r(2) = 0.79-0.99) than for C0 (r(2)= 0.11-0.52). The mean +/- SD values for C0 (microg/L) and C2 (microg/L) for rejectors (n = 3) were 215 +/- 68 and 949 +/- 204 versus 242 +/- 62 and 1359 +/- 474 for the nonrejectors (P = 0.66 and 0.12, respectively). Fisher exact test P values using the median as threshold value for C0 and C2 (234 microg/L and 1251 microg/L, respectively) were 0.6 and 0.1. Analysis of the data revealed that C0 values in rejectors have wider variability than C2. There were no rejectors among the 16 patients exceeding the C2 median value; for C0, however, there was not an easily identifiable threshold value. There is a trend for a significant relationship between C2 and the incidence of rejection, but the number of rejectors was too small to reach statistical significance. A prospective concentration-control de novo study design is recommended as the most appropriate way to fully evaluate the potential utility of C2 monitoring in heart transplant patients.

Immunosuppressive drug monitoring - what to use in clinical practice today to improve renal graft outcome

Therapeutic drug monitoring (TDM) of immunosuppressive therapy is becoming an increasingly complex matter as the number of compounds and their respective combinations are continuously expanding. Unfortunately, in clinical practice, monitoring predose trough blood concentrations is often not sufficient for guiding optimal long-term dosing of these drugs. The excellent short-term results obtained nowadays in renal transplantation confer a misleading feeling of safety despite the fact that long-term results have not substantially improved, definitely not to a point where longer graft survival could counteract the increasing need for transplant organs and less toxicity and side-effects could ameliorate patient survival. It is therefore a challenging task to try to tailor immunosuppressive drug therapy to the individual patient profile and this in a time-dependent manner. For the majority of currently used immunosuppressive drugs, measurement of total drug exposure by determination of the dose-interval area under the concentration curve (AUC) seems to provide more useful information for clinicians in terms of concentration-exposure and exposure-response as well as reproducibility. To simplify this laborious way of measuring drug exposure, several validated abbreviated AUC profiles, accurately predicting the dose-interval AUC, have been put forward. Together with an increasing knowledge of the time-related pharmacokinetic behaviour of immunosuppressive drug and their metabolites, studies are focusing on how to apply abbreviated AUC sampling methods in clinical transplantation, taking into account the numerous factors affecting drug pharmacokinetics. Eventually, TDM using abbreviated AUC profiles has to be prospectively tested against classic methods of drug monitoring in terms of cost-effectiveness, feasibility and clinical relevance with the ultimate goal of improving patient and graft survival.

Immunosuppressant Drug Monitoring: Is the Laboratory Meeting Clinical Expectations?

OBJECTIVE:

To review the literature relating to immunosuppressant drug measurement as performed in therapeutic drug monitoring laboratories associated with transplantation centers and consider whether the assay methods widely used for patient dosage management achieve acceptable quality criteria in the context of other sources of variability with these drugs.

DATA SOURCES:

Articles used were accessed primarily through MEDLINE, as well as references cited in related publications. Searches were restricted to organ transplantation in humans.

STUDY SELECTION AND DATA EXTRACTION:

Emphasis was placed on the literature relating to the quality of immunosuppressant drug assays, their limitations, and evidence of clinical benefit in dosage individualization.

DATA SYNTHESIS:

There is a dilemma evident between the quality of the analytical services offered by some diagnostic immunoassay manufacturers and the ability of a significant number of clinical laboratories globally to select only appropriate assay methods.

CONCLUSIONS:

In many cases, clinical laboratories fail to meet the reasonable clinical expectations required for interpretation of immunosuppressant drug assay results as an adjunct to optimal dosage individualization and patient care.

Evolution of the therapeutic drug monitoring of cyclosporine

The argument for the therapeutic monitoring of cyclosporin A (TDM-CyA), to optimize efficacy and safety, has been discussed in the last 25 years and it is still debated. Although CyA has been for more than 20 years the mainstay of immunosuppression in organ transplantation, no consensus has yet been achieved on TDM-CyA. The first proposed use of CyA was at fixed doses, but this was soon abandoned, and the predose, trough C0 blood level concept was introduced as a tool for TDM-CyA; however, no correlation could ever be shown between the various proposed trough therapeutic windows and major clinical events. On the contrary, the TDM-CyA of full area-under-the-curve (AUC) 0-12 exposure, significantly correlated with acute rejection and renal toxicity. The use of Neoral demonstrated that the region of most variability in CyA pharmacokinetics and the greatest calcineurin inhibition were confined within the AUC0-4, introducing the concept of absorption profiling. A further simplification come from the demonstration that C2, the single blood concentration measurement 2 hours after Neoral administration, was a significant accurate predictor of AUC0-4. The TDM-CyA with C2 has now been clinically validated in kidney, liver, and heart transplant recipients. In the last 25 years of TDM-CyA, some concepts have become clear: inadequate CyA exposure is a key risk factor for acute rejection and may contribute to the development of chronic rejection; C0 predose monitoring does not accurately measure CyA exposure. Thus, C2 single sampling offers today an innovative, simple, and accurate alternative for the pharmacokinetic clinical monitoring of CyA.

Cyclosporine levels at 2 hours after dose and body mass index in relation to graft function in renal transplant patients treated with azathioprine or mycophenolate mofetil

The aim of this study was to evaluate the effect of C(2) levels on renal graft function in relation to body mass index (BMI). This retrospective study of 95 renal transplant patients included 53 on AZA and 42 on MMF at 3.1 years after transplantation. The cohort was divided into groups according to their C(2) levels, namely <600 ng/mL, 600 to 900 ng/mL, or >900 ng/mL, and according to BMI (>26 kg/m(2)). In every group, we evaluated the percentage of patients with an increase in creatinine by 1 mg/dL or >/=50% from the first year posttransplant. There was no difference in age, gender, graft source, and dose of corticosteroids or CsA between the groups. Patients on AZA with C(2) 600 to 900 ng/mL showed a lower prevalence of renal dysfunction (3.4%) than those with C(2) levels <600 ng/mL (14.3%) or >900 ng/mL (20%). Seventeen percent of the patients on AZA and 11.9% on MMF had BMI >26 kg/m(2) (P = NS). An increased serum creatinine was present in 22.2% of patients with BMI >26 kg/m(2) in the AZA group vs 20% in the cohort MMF (P = NS). These findings suggest that long-standing renal recipients on AZA with C(2) levels of between 600 and 900 ng/mL show better preservation of renal function. We did not identify differences on the basis of C(2) levels in MMF-treated recipients. The influence of BMI on long-term graft function seemed to be independent of AZA or MMF therapy.

Use of cyclosporine in renal transplantation

The first cyclosporine trials in renal transplantation began in Cambridge in 1978. Between 1982 and 1985 several large multicenter trials and the reports from large series of patients evidenced that cyclosporine was a major advance in the prevention of acute rejection episodes and in improving short-term and long-term graft survival. Cyclosporine also showed the capacity to mitigate immunologic risk factors, HLA mismatching, and lack of pretransplant transfusions. However, cyclosporine has the serious defect of being nephrotoxic. Induction therapy with OKT3, polyclonal antibodies, and more recently with anti IL-2R monoclonal antibodies allowed the delay of introduction cyclosporine in patients showing posttransplant graft dysfunction. Other relatively unsuccessful attempts for overcoming cyclosporine nephrotoxicity were made before the association of new xenobiotics such as mycophenolate mofetil or sirolimus permitted cyclosporine doses to be reduced. These combinations reduce acute rejection incidence to below 20%, with its consequent positive impact on long-term graft outcome and also allow a safer steroid sparing and withdrawal early posttransplantation. Also, the association of cyclosporine with other new compounds such as the lymphocyte homing FTY20 or the peripheral lymphocyte-depleting Campath-1-IgG is currently under clinical investigation. Cyclosporine's future place is yet to be established in the new era of immunosuppression.

The value of C2 monitoring in stable renal allograft recipients on maintenance immunosuppression

BACKGROUND

Cyclosporin A (CyA) is a drug with a narrow therapeutic window and highly variable pharmacokinetics. Therapeutic drug monitoring is essential and conventionally has been guided by trough levels (C0). Recent evidence indicates that a single blood concentration measurement 2 h after CyA administration (C2) is a more accurate predictor of drug exposure and clinical events than determination of C0. To date, limited prospective data are available with respect to risks and benefits of C2 monitoring in renal transplant recipients, and little experience exists with C2 monitoring in maintenance patients.

METHODS

In 127 long-term renal allograft recipients, we determined C2 levels in addition to conventional C0 and observed clinical outcome over a period of 13.6 +/- 3.1 months. To determine the precision of monitoring, we repeatedly determined C0 and C2 levels in 46 stable patients without dose change.

RESULTS

Clinical outcome was excellent (patient survival 100%, graft survival 97%), with only two borderline rejections, although C2 levels (564 +/- 186 ng/ml) were lower than recommended so far for maintenance patients. We found no significant differences in C2 levels between patients with rejection and CyA toxicity. Receiver operating characteristic (ROC) analysis showed no prediction for risk of rejection, toxicity or infection by C2 levels. Repeated determinations of both C0 and C2 levels in 46 patients revealed a high intra-patient variability. In these patients, the coefficient of variation for C2 was only marginally better compared with C0.

CONCLUSIONS

We conclude that in maintenance patients, C2 concentrations between 500 and 600 ng/ml are well tolerated and provide effective and safe rejection prophylaxis. Although mean C2 levels do not seem to be helpful in identifying patients at risk for rejection, they may be useful to detect over-immunosuppression and to improve long-term allograft survival further by reducing CyA nephrotoxicity.

Review of the proliferation inhibitor everolimus

Everolimus (Certican) is being developed for prevention of acute and chronic rejection of solid organ transplants. A novel proliferation inhibitor, everolimus synergies with cyclosporine to prevent and reverse acute rejection in preclinical models of kidney, heart or lung transplantation. The manifestations of chronic rejection that may contribute to graft loss are also inhibited by everolimus in preclinical models. Although everolimus is metabolised by the cytochrome P450 CYP3A isoenzyme, coadministration with cyclosporine does not alter the pharmacokinetics of cyclosporine, but cyclosporine coadministration increases exposure to everolimus. Everolimus interacts with inhibitors and inducers of this system; its clearance is reduced in patients with hepatic impairment. In an immunosuppressive regimen with cyclosporine microemulsion formulation and corticosteroids, transplant recipients treated with everolimus show low rates of acute rejection and, in one heart and one renal trial, lower rates of cytomegalovirus infection. Acute rejection rates are lower than those seen with azathioprine in cardiac transplant recipients and similar to those seen with mycophenolate mofetil in renal transplant recipients. Low rates of acute rejection are maintained when everolimus is given as part of a quadruple immunosuppressive regimen with low-dose cyclosporine in renal transplant recipients, with the added benefit of better renal function compared with full-dose cyclosporine. Use of C(2) monitoring to optimise cyclosporine exposure and enhance efficacy and safety of everolimus is planned in future studies. Hypertriglyceridaemia and hypercholesterolaemia have been associated with everolimus, but these effects are not dose-limiting. There is no clear upper therapeutic limit of everolimus. However, thrombocytopenia occurs at a rate of 17% at everolimus trough serum concentrations above 7.8 ng/ml in renal transplant recipients. There are limited safety data available in patients with trough concentrations > 12 ng/ml. Studies suggest everolimus targets primary causes of chronic rejection by reducing acute rejection, allowing for cyclosporine dose reduction (which may lead to improved renal function relative to full-dose cyclosporine) and by reducing cytomegalovirus infection and inhibiting vascular remodelling.

New concepts in cyclosporine monitoring

PURPOSE OF REVIEW

Inadequate cyclosporine exposure is a key risk factor for acute rejection, and may contribute to the development of chronic rejection and graft failure. Pre-dose monitoring does not accurately measure drug exposure because of extensive inter- and intra-patient variability in cyclosporine absorption and metabolism. Limited sampling, using individual timed specimens, offers a new, simple and accurate alternative for clinical monitoring of cyclosporine.

RECENT FINDINGS

The area under the first 4 h of the concentration-time curve (AUC ) and the single-point concentration at 2 h post-dose (C2) are key measures of cyclosporine exposure. De novo studies show that achieving an AUC value of more than 4400 microg.h/l or a C2 level of 1500-2000 microg/l during the first 5 days post-transplant minimizes the risk of rejection and improves graft function. Maintenance studies suggest that reducing the C2 level to approximately 800 microg/l after 3-6 months may improve the serum creatinine level, blood pressure, general well-being and reduce adverse effects.

SUMMARY

Single-point C2 monitoring can be implemented quickly and simply with appropriate site and patient training. The timing of phlebotomy is more critical, but immunoassay bias is lower with 2 h post-dose than with trough level measures. Single-point C2 monitoring may be effective in liver and heart replacement, but initial target levels for liver transplantation are lower because cyclosporine is transported directly to the liver via the portal system. C2 monitoring is now being widely adopted as an accurate and practical measure of drug exposure, and can be combined with pharmacodynamic methods to optimize immunosuppression.

Universal approach to pharmacokinetic monitoring of immunosuppressive agents in children

Current data indicate that pharmacokinetic (PK) monitoring of cyclosporin microemulsion (CsA) should be performed using the 2-h concentration (C2), that tacrolimus (Tac) is commonly monitored using the trough level, and mycophenolate mofetil (MMF) should be monitored using the 1-h (C1), 2-h (C2) and 6-h (C6) concentrations. The three differing time-point requirements are cumbersome, and we aimed to develop universal guidelines for all three drugs using a large number of full PK profiles in children. One-hundred and twenty two stable pediatric patients, receiving either CsA (165 PK profiles, 69 patients, 24 with concomitant MMF) or Tac (122 PK profiles, 53 patients, 18 with MMF) were analyzed retrospectively. Pearson r for the CsA C2 was 0.90 [95% confidence interval(CI): 0.86-0.92], for Tac C2 r was 0.86 (95% CI: 0.80-0.90), and for MPA C2 r was 0.77 (95% CI: 0.68-0.83), respectively. For MPA, at least three time-points are required to accurately estimate the area under the concentration-time curve (AUC), and C1, C2 and C6 serve as best markers. Excellent AUC estimations could be obtained from a limited sampling strategy from C1, C2 and C6 or C0, C1, C2 and C4 with clinically acceptable errors for all three drugs. The AUC can be estimated with great precision by using an identical approach for all three drugs. Target AUCs for a given time-point after transplantation remain to be established.

Comparison of trough, 2-hour, and limited AUC blood sampling for monitoring cyclosporin (Neoral) at day 7 post-renal transplantation and incidence of rejection in the first month

The use of alternative strategies to the traditional pre-dose/trough (C0) blood sampling for cyclosporine (CsA) therapeutic drug monitoring has the potential to revolutionize analytical practices which have, in many centers, been established for some 20 years. While the C0 sample has previously been recommended, current attitudes are increasingly proposing alternatives for assessing CsA exposure, including various limited sampling strategies of the AUC (lssAUC) in the early postdose period, or alternative single-point nontrough samples, such as a 2-hour postdose sample (C2). The present study has reviewed a series of consecutive renal transplant recipients over 18 months where CsA was the primary immunosuppressant. The lssAUC performed at around day 7 posttransplantation included drawing blood at 0, 2, and 4 hours postdose, giving AUC(0-4). The aim of this study was to review the occurrence of acute biopsy-proven rejection in the first month and consider which of (simultaneously measured) C0, C2 or AUC(0-4) was a better early indicator of this adverse outcome. The result was best described by comparing the data from rejectors (n = 13) and nonrejectors (n = 42) for these 3 indices of CsA exposure (i.e., C0, C2 or AUC(0-4)). There was no evidence that C0 predicted the likelihood of such adverse clinical outcomes. In contrast, rejectors tended to have lower mean C2 CsA concentrations, and the incidence of rejection was 0.0 when C2 exceeded 1200 microg/L (n = 10). While the data are limited in the higher C2 CsA concentration range, it is nevertheless consistent with more recent recommendations suggesting that the CsA at C2 should target 1700 microg/L in this first month posttransplantation. As 64% of the patients were also receiving a CsA-sparing agent (diltiazem [DTZ]), the relationships were also investigated to determine whether any affect of concomitant DTZ therapy could be demonstrated. However, in this small sample, no significant affect of DTZ was seen.

Maximum a posteriori Bayesian estimation of oral cyclosporin pharmacokinetics in patients with stable renal transplants

OBJECTIVE

To develop a maximum a posteriori probability (MAP) Bayesian estimator for the pharmacokinetics of oral cyclosporin, based on only three timepoints, and evaluate its performance with respect to a full-profile nonlinear regression approach.

PATIENTS

20 adult patients with stable renal transplants given orally administered microemulsified cyclosporin and mycophenolate.

METHODS

Cyclosporin was assayed by liquid chromatography-mass spectrometry. Nonlinear regression and MAP Bayesian estimation were performed using a home-made program and a previously designed pharmacokinetic model including an S-shaped absorption profile described by a gamma distribution.

OUTCOME MEASURES AND RESULTS

MAP Bayesian estimation using the best limited sampling strategy (before administration, and 1 and 3 hours after administration) was compared with nonlinear regression (taken as the reference method) for the prediction of the different pharmacokinetic parameters and exposure indices. Median relative prediction error was -0.49 and -3.42% for area under the concentration-time curve over the administration interval of 12 hours (AUC12) and estimated peak drug concentration (Cmax), respectively (nonsignificant). Relative precision was 2.00 and 4.32%, and correlation coefficient (r) was 0.985 and 0.955, for AUC12 and Cmax, respectively.

CONCLUSION

This paper reports preliminary results in a stable renal transplant patient population, showing that MAP Bayesian estimation can allow accurate prediction of AUC12 and Cmax with only three samples (0, 1 and 3 hours). Although these results require confirmation by further studies in other clinical settings, using other drug combinations, other analytical methods and commercially available pharmacokinetic software, the method seems promising as a tool for the therapeutic drug monitoring of cyclosporin in clinical practice or for exposure-controlled studies.

Improved clinical outcomes for liver transplant recipients using cyclosporine monitoring based on 2-hr post-dose levels (C2)

BACKGROUND

A prospective, open-label, study was conducted at 29 centers in 9 countries, involving 307 de novo liver transplant patients to compare the clinical usefulness of monitoring 2-hr post-dose cyclosporine (CsA) levels (C2) with conventional trough cyclosporine blood levels (pre-dose) (C0).

METHODS

Neoral oral therapy was initiated at 15 mg/kg/day and dose adjusted according to predetermined C2 or C0 target level ranges. The primary efficacy variable was treatment failure at 3 months, where evaluation was based on a composite endpoint of biopsy-proven rejection, treatment for rejection, graft loss, death, or premature withdrawal/discontinuation from the study.

RESULTS

Baseline characteristics were similar between groups. Graft loss at 12 weeks (retransplantation or death) occurred in 6.8% C2 and in 7.0% C0 patients. Overall incidence of treated acute rejection was lower for C2 (23.6%) than C0 patients (31.6%) (P=0.144, Cochran-Mantel-Haenszel [CMH] test). In hepatitis C virus (HCV)-negative patients, the incidence of rejection in the C2 group was significantly less than in the C0 group (21.2% vs. 33.0%; P<0.05), whereas in HCV-positive patients, the rejection rate was similar in both groups (26.7% for C2 group vs. 27.3% for C0 group: P=0.81). C2 patients (n=16) who reached minimum target CsA levels by day 3 had a notably low incidence of rejection (12.5%), whereas there was no difference in the incidence of rejection in C0 patients, irrespective of time to reach target level. For biopsy-proven acute rejections (21.6% for C2 vs. 30.4% for C0), the incidence of moderate and severe histological diagnosis was significantly lower in the C2 group than in the C0 group (47% vs. 73%; P=0.01). Safety profiles were similar between the two groups, with few patient withdrawals due to adverse events (9.5% for C2; 7.0% for C0).

CONCLUSIONS

Using C2 monitoring, the overall incidence of acute cellular rejection was lower compared with the C0 group, and the histological severity of acute rejections was shown to be significantly milder for the C2 group, indicative of good long-term prognosis. These data demonstrate that the use of C2 monitoring is superior to C0 and results in a reduction in the incidence and severity of acute cellular rejection without detrimental effect on the drug safety profile.

Two-hour cyclosporine concentration determination: an appropriate tool to monitor neoral therapy?

Cyclosporine is a critical dose drug for which individualisation by therapeutic drug monitoring is indisputable. Current evidence suggests that a single concentration (C2) taken two hours after cyclosporine administration with the microemulsion formulation better predicts exposure and events than the trough concentration (C(0)), which is routinely used for adjusting the dosage of this drug. Studies have shown that the greatest calcineurin inhibition and the maximum inhibition of IL-2 production occur in the first 1 to 2 hours after dosing. These findings support the concept that the C2 level better reflects immunosuppressive efficacy than the trough concentration. Preliminary data from an outcome study in liver transplant recipients have shown that the incidence of biopsy proven moderate to severe acute rejection was significantly lower in patients managed by C2 monitoring compared with those monitored by C(0). The critical importance of achieving adequate cyclosporine exposure during the first 3 to 5 posttransplant days to prevent acute rejection has been documented in prospective studies with de novo renal and liver transplant recipients. Conversion of maintenance liver and heart transplant patients to C2 monitoring resulted in an amelioration of renal function. Time-dependent target values have been proposed for liver and renal transplant recipients. These require further prospective validation. For routine monitoring of C2 levels on-site validated dilution guidelines are necessary for most of the available immunoassays. C2 monitoring necessitates further organizational requirements which may be judged differently between transplant centers. In particular during the early posttransplant period C2 monitoring is a promising new option to make immunosuppressive therapy with the microemulsion formulation of cyclosporine safer and more efficient.

Randomized, international study of cyclosporine microemulsion absorption profiling in renal transplantation with basiliximab immunoprophylaxis

Increasing information suggests that absorption profiling may be superior to trough level monitoring for optimal concentration control of cyclosporine microemulsion (Neoral) therapy, and that CsA exposure early post-transplant may correlate significantly with reduced risk of acute graft rejection. This randomized, prospective, multicenter international concentration-controlled study was conducted in 21 renal transplant centers in 8 countries to test and compare the clinical feasibility, functionality, accuracy, precision and prediction of rejection by cyclosporine microemulsion absorption profiling to conventional trough-level drug monitoring. Primary or second renal allograft recipients treated with basiliximab, cyclosporine microemulsion and prednisone immunosuppression were randomized to two study groups in which cyclosporine microemulsion therapy was monitored using a multipointalgorithm or by trough levels. The two study arms were comparable in terms of baseline characteristics, treatment and clinical outcomes. Treatment failure, consisting of acute rejection, graft loss or death, occurred with equal incidence in the two groups (30% and 33%, respectively). Diagnostic feasibility, measured as the proportion of samples obtained within the designated time window, was marginally lower in area under the time-concentration curve (AUC) than in trough groups, but the therapeutic accuracy and precision were comparable or superior in the AUC group. Cox regression analysis performed across study groups showed a highly significant correlation between the predicted probability of acute rejection and cyclosporine (CsA) exposure measured by AUC over the entire 12-h dosage interval (AUC[0-12]) (p = 0.0068), AUC over the first 4 h of the 12-h dosage interval (AUC[0-4]) (p = 0.0014) or 2h post-dose (C2) CsA level (p = 0.0027). Day 3 dose- and weight-corrected C2 values (EMIT equivalent) separated patients into low (< 200 microg/L/mg/kg dose), intermediate (200-350 microg/L/mg/kg dose) and high absorber categories (> 350 microg/L/mg/kg dose), defining those at greatest risk. Within these categories, C2 values above approximately 1500 microg/L by day 3 post-transplant were associated with the lowest predicted probability of rejection. Comparable analysis by Cox regression using C0 levels did notreach statistical significance. Absorption profiling is a feasible, accurate and precise method for monitoring cyclosporine microemulsion therapy in clinical practice and, as shown in the companion article, may be simplified by the use of single-point C2 concentrations which accurately predict individual AUC[0-4] exposure levels. Both cyclosporine microemulsion relative absorption (i.e. dose- and weight-corrected exposure) and CsA exposure (measured by predicted AUC or C2 levels) are closely correlated with the risk of rejection, and define patients at high and low risk of acute graft rejection. Trough (C0) levels are not closely correlated with either CsA exposure or rejection risk, and should not be considered reliable for monitoring cyclosporine microemulsion therapy.

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.

A limited sampling strategy for cyclosporine area under the curve monitoring in lung transplant recipients

We developed a limited sampling strategy (LSS) for predicting cyclosporine (Neoral) area under the curve from concentration-time data obtained specifically from lung transplant recipients. The optimal and most clinically convenient LSS for lung transplant recipients, based on patient wait time, number of blood samples required, percent prediction error, and assessment of predictive performance is one that requires 2 blood samples collected at 1 and 3 hours post-dose: AUC = 1.75 x C(1) + 4.91 x C(3) + 185.62.

Limited sampling strategies for estimating cyclosporin area under the concentration-time curve: review of current algorithms

Cyclosporin, the drug of first choice in transplantation surgery, is characterized by a low therapeutic index and variable absorption, so close monitoring of the drug is required to optimize the dosing. Predose blood cyclosporin levels are measured routinely for therapeutic monitoring, but this approach is not optimal because the area under the concentration-time curve (AUC) correlates better with clinical events. However, conventional methods of measuring AUC require many blood samples, which is not viable in a routine clinical setting. AUC monitoring can be simplified for use in a clinical setting by using a limited sampling strategy (LSS) that allows AUC to be estimated using a small number of blood samples collected at specific times. This article reviews the current literature on estimating cyclosporin AUC using LSS. Thirty-eight papers suggesting the use of specific time points were found. LSS has been developed for different transplant types, with different dosing regimens, and with different assays. Most authors suggested either two- or three-sample equations. Results from authors who validated their models suggest that equations defined on one transplant type may be applicable to other transplant types, to both adults and children, and to early or late after transplantation. Moreover, it seems that there is flexibility in the choice of equations available to clinicians. The number of samples to collect for accurate estimations is a matter of debate, but a wise choice can minimize the number. The choice of the optimal LSS and validation are discussed.

Evaluation of limited sampling strategies for estimation of 12-hour mycophenolic acid area under the plasma concentration-time curve in adult renal transplant patients

Mycophenolate mofetil, the oral prodrug of mycophenolic acid, is indicated as immunosuppressive therapy after renal transplantation. To aid in the investigation of pharmacokinetic-pharmacodynamic relationships of mycophenolic acid in the clinical setting, limited blood sampling strategies have been proposed, and models from these developed, for the estimation of mycophenolic acid area under the concentration-time curve (AUC). In the current study, the authors investigated the predictive performance of six published models to estimate AUC. A total of 49 profiles from 25 renal transplant patients were used to test each model's performance against a full 14 time-point AUC. A wide range of agreement was found when predicted AUCs were compared with full AUCs using linear regression analysis (range: r2 = 0.499 to 0.836). Model 1, which uses 4 time-points over 6 hours, was found to be superior to all other models. The range of time-points used in this model takes into account patients with variable absorption. This model should be further tested on data sets from other centers. The relatively poor performance of the other models may be caused by their inability to describe the peak concentration in these patients. Caution is warranted when using limited sampling strategies on patients whose absorption of mycophenolic acid is altered, compared with those of the pharmacokinetic profiles from which the model was developed.

New oral formulation of cyclosporin A (Neoral) pharmacokinetics in allogeneic bone marrow transplant recipients

Cyclosporin A (CsA) absorption is variable in bone marrow transplant (BMT) patients compromising the efficacy of graft-versus-host disease prevention. Neoral, a new microemulsion formulation of CsA which has an improved bioavailability, increases intestinal absorption of the drug with less variable pharmacokinetic parameters in non-BMT patients. In order to predict the best dosage of Neoral when patients are switched from i.v. to oral administration we performed a randomised study comparing two oral doses, either the same or twice the last i.v. dose used after BMT. Fourteen adults were randomised around day 25 after BMT. Whole blood CSA concentrations were measured 2 and 12 h after the oral administration of Neoral on days 0, 7 and 14 to determine residual and maximum concentration, and modified whenever necessary to maintain blood level CsA concentration within therapeutic range (150-250 ng/ml). We found that patients who received twice the last i.v. dose had better concentrations than patients from the other group while toxicity was identical in both groups. We conclude that doubling the last i.v. dose during the switch to oral administration of Neoral gives the best therapeutic range concentration and should be recommended for graft-versus-host prevention.

Methods for clinical monitoring of cyclosporin in transplant patients

Cyclosporin was introduced into clinical practice in the early 1980s and has since been shown to prolong survival for transplant recipients. Because cyclosporin is a narrow therapeutic index drug and there are significant consequences associated with 'subtherapeutic' and 'supratherapeutic' concentrations, cyclosporin therapy is monitored as part of routine patient follow-up. However, the optimal method for the therapeutic drug monitoring of cyclosporin has yet to be defined. Currently, the most common method involves monitoring pre-dose trough concentrations, but this method is less than ideal. Other methods of monitoring cyclosporin therapy include monitoring the area under the concentration-time curve, limited sampling strategies, monitoring of single concentrations other than troughs and pharmacodynamic monitoring. Bayesian forecasting has been used successfully in clinical practice with other drugs with narrow therapeutic indices. However, few studies are available regarding Bayesian forecasting and cyclosporin. Existing studies are preliminary in nature and involve the old Sandimmun formulation rather than the Neoral formulation. Although these methods show promise, they have not gained widespread acceptance. This is because of their impracticality and the lack of prospective studies comparing other monitoring methods with trough concentration monitoring. Further comparative studies evaluating the impact of the specific monitoring method on definite patient outcomes are warranted.

Cyclosporin assays, metabolite cross-reactivity, and pharmacokinetic monitoring

The range of cyclosporin (CsA) immunoassays has become the mainstay in many therapeutic drug monitoring laboratories for delivering CsA concentration data to support clinical care of patients after transplantation. However, these assays have been criticized because of the varying degree of CsA-metabolite interferences that introduce analytical errors. The introduction of another such CsA assay (on the AXSyM analyzer) has been considered, as the manufacturer has represented it as having a low CsA-metabolite cross-reactivity profile compared with chromatographic methods. A case is presented to question how this apparent result was obtained in view of the method using the same antibody as another CsA method from the same manufacturer (fluorescence polarizaton immunoassay on the TDx analyzer) which is well known to have poor performance in regard to CsA-metabolite cross-reactivity. The implications for this problem may be even more serious as more patients are monitored using the CsA AUC strategies, rather than the traditional trough concentration approach. Such issues reinforce the need for the clinical laboratory to be critical of methods offered commercially based on scientific/pharmacologic skills.

Pharmacoeconomics of therapeutic drug monitoring in transplantation

Immunosuppressive drugs have contributed significantly to the success of organ transplantation. Therapeutic drug monitoring is an integral part of transplant protocols. However, there is little information concerning its positive contribution to pharmacoeconomics. Before developing studies to demonstrate the potential benefits of TDM, consideration must be given to the type of TDM to be evaluated. It is argued that, given that the lymphocyte in the central compartment is the target for immunosuppressants, Area-Under-the-Curve monitoring may be a better reflection of control and toxicity than traditional trough monitoring.