Sandimmune to Neoral conversion and value of abbreviated AUC monitoring in stable pediatric kidney transplant recipients

Development of a Pediatric Relative Bioavailability/Bioequivalence Database and Identification of Putative Risk Factors Associated With Evaluation of Pediatric Oral Products

Generally, bioequivalence (BE) studies of drug products for pediatric patients are conducted in adults due to ethical reasons. Given the lack of direct BE assessment in pediatric populations, the aim of this work is to develop a database of BE and relative bioavailability (relative BA) studies conducted in pediatric populations and to enable the identification of risk factors associated with certain drug substances or products that may lead to failed BE or different pharmacokinetic (PK) parameters in relative BA studies in pediatrics. A literature search from 1965 to 2020 was conducted in PubMed, Cochrane Library, and Google Scholar to identify BE studies conducted in pediatric populations and relative BA studies conducted in pediatric populations. Overall, 79 studies covering 37 active pharmaceutical ingredients (APIs) were included in the database: 4 bioequivalence studies with data that passed BE evaluations; 2 studies showed bioinequivalence results; 34 relative BA studies showing comparable PK parameters, and 39 relative BA studies showing differences in PK parameters between test and reference products. Based on the above studies, common putative risk factors associated with differences in relative bioavailability (DRBA) in pediatric populations include age-related absorption effects, high inter-individual variability, and poor study design. A database containing 79 clinical studies on BE or relative BA in pediatrics has been developed. Putative risk factors associated with DRBA in pediatric populations are summarized.

High intra-individual variability of cyclosporine pharmacokinetics in lung transplant recipients without cystic fibrosis

BACKGROUND

There has been little study on the variability of CsA pharmacokinetics in stable lung transplant (LT) recipients without cystic fibrosis. This study was conducted to determine the prevalence of high intra-individual variability of CsA in LT recipients and its implications in CsA monitoring.

METHODS

Twenty-nine pharmacokinetic curves were performed in 10 consecutive stable patients from a single center. The intra-individual coefficient of variation (CV) of the AUC₀₋₁₂ h was calculated in each case. Patients were grouped according to whether their CV was high (≥20%) or low (<20%). Correlations between cyclosporine CsA concentration at each time point, AUC₀₋₄ h , and AUC₀₋₁₂ h were also calculated.

RESULTS

Six (60%) patients presented low CVs and four (40%) high CVs. In patients with low CVs, the best correlation of AUC₀₋₁₂ h was with CsA concentration at two h post-dose (C₂) (r = 0.674, p = 0.002), whereas in those with high CV, the best correlation was with C5 (r = 0.800, p = 0.003). In the latter group, the correlation with C₂ was low (r = 0.327, p = 0.32), whereas the correlation with C₀ was high (r = 0.709, p < 0.05).

CONCLUSIONS

Intra-individual variability of CsA pharmacokinetics may be high in many LT recipients. In patients with high CV, the use of C₀ levels may be more appropriate for CsA monitoring than C₂ levels.

Pharmacokinetics of tacrolimus in stable paediatric renal transplant recipients

Because tacrolimus (Tac) has a narrow therapeutic index and highly inter- and intra-individual variable pharmacokinetic (PK) characteristics, monitoring of drug exposure is recommended, but limited data are available on the kinetics of Tac in paediatric renal transplant recipients, especially of limited sampling strategies. To investigate the correlation between Tac trough level (TL) and the 0-12 h area under the curve (AUC), and the value of abbreviated AUC monitoring, we evaluated 12 h PK profiles in 27 children at least 1 year after transplantation. There was a significant discrepancy between Tac TLs and 0-12 h AUC (r = 0.60). Every time point, different from C(0), gave a better prediction for the drug exposure, with C(4) and C(6) as best predictors (r = 0.93 and r = 0.92, respectively). The 0-12 h AUC was estimated with great precision by the use of a two- or three-point sampling strategy, and the latter is more time-point independent. In paediatric renal transplant recipients on Tac maintenance therapy, whose condition is stable, Tac TL is not a reliable tool for the estimation of drug exposure. Abbreviated monitoring, especially at three points in time, give reliable predictions of the complete 0-12 h AUC. We suggest a 0-12 h AUC of around 150 ng x h/ml for stable paediatric renal transplant recipients 1 year after transplantation and around 100 ng x h/ml in the following years. Target AUC values should be further established for paediatric transplant recipients according to the time after transplantation.

Renal function with cyclosporine C2 monitoring, enteric-coated mycophenolate sodium and basiliximab: a 12-month randomized trial in renal transplant recipients

BACKGROUND

Cyclosporine exposure, as estimated by the area under the curve (AUC), predicts outcomes in renal transplantation. Cyclosporine concentration at two h post-dose (C(2)) has been shown to be the most reliable, single-point surrogate marker for AUC. The objective of this study was to measure renal function beyond month 2 post-transplant using two different C(2) maintenance targets in combination with enteric-coated mycophenolate sodium (EC-MPS), corticosteroids, and basiliximab induction.

METHODS

In this open-label, multicenter trial, renal transplant recipients entered one of two randomized groups at day 61 post-transplant: group A (higher-C(2) range) or group B (lower-C(2) range).

RESULTS

Patients (164) were recruited, and 141 patients were entered the randomized groups (group A, n = 66; group B, n = 75). At 12 months, the mean calculated creatinine clearance was significantly greater in group B than in group A (79.2 vs. 71.0 mL/min, p < 0.05). Biopsy-proven acute rejection occurred in 14.7% patients in group B and in 24.2% patients in group A (n.s.). During the 12-month trial, 17.7% patients discontinued EC-MPS because of adverse events. Group B (44.0%) had fewer serious adverse events when compared with group A (62.1%; p = 0.04). Overall patient and graft survival were 99.4% and 95.7% respectively. Among 99 high-risk patients (i.e., African-American race, previous transplant, PRA >35% or >4 HLA mismatches), mean creatinine clearance at 12 months was 65.6 mL/min and biopsy-proven rejection occurred in 20.2% patients.

CONCLUSIONS

Low cyclosporine C(2) levels are associated with improved renal function compared with higher C(2) levels when used in conjunction with EC-MPS, steroids and basiliximab induction. EC-MPS with low cyclosporine C(2) levels, corticosteroids and basiliximab provides excellent renal function with good efficacy even in high-risk patients.

Immunosuppression in pediatric solid organ transplantation

This report reviews the immunosuppressive regimens that are used in pediatric transplantation. There are predominant themes developing in the field involving the minimization of the total exposure of immunosuppression through limiting the number of agents and newer pharmacokinetic modeling. Calcineurin inhibitors are the foundation of most immunosuppressive regimens. However, there are new pharmacologic monitoring techniques to reduce the potential for long-term side effects of this class of agents. Although tacrolimus remains one of the mainstays of current protocols, there are strides being made to reduce the patient's long-term exposure to it with transitioning to sirolimus. Corticosteroids are still used predominantly, but there is growing evidence of successful steroid-sparing protocols that are as effective and avoid the chronic morbidity of steroids. Antibody induction therapy remains a standard with clearer evidence of the efficacy of IL-2 receptor antagonists. There is preliminary clinical evidence that polyclonal antibody therapy is efficacious in pediatric transplantation. Future studies will determine the best way to assess the functional immune status of a pediatric transplant recipient to maintain the fine balance and avoid the complications of either excessive or inadequate immunosuppression.

Early Cyclosporine C0 and C2 Monitoring in De Novo Kidney Transplant Patients: A Prospective Randomized Single-Center Pilot Study

BACKGROUND

C2 monitoring of cyclosporine (CsA) has been promoted as improving the results of organ transplantation. No randomized, controlled studies in de novo kidney transplant recipients are available.

METHODS

Between June 2003 and August 2004, 160 consecutive cadaveric kidney recipients allocated to CsA, mycophenolate and steroids were randomized to either C0 or C2 monitoring of CsA for the first 3 weeks posttransplant. Both levels were measured, keeping the other level blinded until 3 weeks. Altogether, 1451 double measurements were done. The target C0 was 200-300 microg/L and C2 1500-2000 microg/L. From the fourth week on, only C0 monitoring was used. Median follow up time was 505 days.

RESULTS

The overall 3-month rejection rate was 7.5% in Group C0 vs. 10.8% in Group C2 and the one-year graft survival rates were 92.5% vs. 94.6% (NS). Rate of delayed graft function was similar in the groups. Plasma creatinine tended to be higher in group C2 at 3 weeks, but not thereafter. During the first three weeks posttransplant, the mean CsA dose was 57%, mean C2 levels were 55%, and mean C0 levels were 98% higher in group C2 than in group C0 (P < 0.00001).

CONCLUSION

This pilot study showed no advantages of C2 monitoring but led to significantly higher CsA doses and blood levels than C0 monitoring.

Cyclosporine drug monitoring with C0 and C2 concentrations in children with stable renal allograft function

Cyclosporin A (CsA) has a narrow therapeutic window and necessitates monitoring of blood concentration. We aimed to evaluate trough (C0) and second hour (C2) level after ingestion of drug monitoring in renal allograft recipients. In this retrospective study, 12 children eight boys and four girls; mean age at transplantation 14.6 +/- 3.7 yr (ranges: 7.0-19.0), mean age post-transplant 17.8 +/- 4.9 yr (ranges: 9.0-24.0) who were transplanted >6 months were enrolled in this evaluation. Ten were recipients of a living related donor and two deceased donor grafts. While six children were receiving CsA, steroids and azathioprine, the other six received CsA, steroids and mycophenolate mofetil. Clinical course, blood pressure, renal and liver function tests were recorded. Mean C0 and C2 were 96.2 +/- 59.5 and 504 +/- 305.4 ng/mL respectively. Mean serum creatinine level was 1.2 +/- 0.45 mg/dL and mean creatinine clearance (CrCl) was 89.2 +/- 36.8 mL/min/1.73 m2. There was a correlation between serum creatinine level, CsA dose and C2 levels,whereas,there was no correlation between age, blood pressure, CrCl and C2 levels. However, no correlation was found between C0 levels and any of the above parameters. In conclusion, our data suggest that C2 levels are correlated better with dose and serum creatinine level.

Monitoring C2 level predicts exposure in maintenance lung transplant patients receiving the microemulsion formulation of cyclosporine (Neoral)

BACKGROUND

Dosing of the microemulsion formulation of cyclosporine (Neoral) is conventionally based on trough levels (C(0)). However, experience in renal transplantation has shown that cyclosporine exposure during the absorption phase (AUC(0-4)) is critical for optimizing immunosuppression, and that cyclosporine (CsA) concentration at 2 hours post-dose (C(2)) shows the closest correlation with AUC(0-4). This study evaluated whether C(2) values correlate more closely with AUC(0-4) than C(0) in lung transplant patients.

METHODS

Pharmacokinetic data were collected prospectively from 20 clinically stable adult lung allograft recipients receiving CsA, mycophenolate mofetil and steroids. Indications for transplantation were emphysema (n = 15), idiopathic fibrosis (n = 2), primary pulmonary hypertension (n = 1), cystic fibrosis (n = 1) and lymphangioleiomyomatosis LAM (n = 1). Blood samples were collected at 0, 1, 2, 3 and 4 hours after administration of CsA, and then AUC(0-4) was calculated. The Correlation between cyclosporine concentration at each time-point and AUC(0-4) was also calculated.

RESULTS

C(2) showed the closest correlation with AUC(0-4) (r(2) = 0.85). C(0) had the poorest correlation of all time-points (r(2) = 0.64). Two patients with radiologic signs of gastroparesis had no peak cyclosporine levels at all and were excluded from the correlation analysis. Mean AUC(0-4) was 3,700 ng . h/ml during Year 1 post-transplant, 2,400 ng . h/ml during Years 1 to 3, and 1,500 ng . h/ml thereafter. Mean C(2) values were 1.2 microg/ml during Year 1, 0.8 microg/ml during Years 1 to 3, and 0.5 microg/ml thereafter.

CONCLUSIONS

C(2) is the single time-point that correlates most closely with AUC(0-4) in lung transplant recipients without gastroparesis. It remains to be demonstrated whether monitoring CsA based on C(2) levels results in a lower incidence of rejection without additional toxicity.

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.

Pharmacokinetic of cyclosporine microemulsion in pediatric kidney recipients receiving A quadruple immunosuppressive regimen: the value of C2 blood levels

BACKGROUND

The management of cyclosporine therapy in pediatric kidney-transplant recipients is largely based on single center's experience rather than on a univocal pharmacokinetic approach based on therapeutic drug monitoring. A prospective multicenter trial was designed to address the question whether C2 blood level monitoring of cyclosporine microemulsion therapy is feasible in the pediatric setting.

METHODS

Sixty-four pediatric kidney-transplant recipients receiving a triple immunosuppressive regimen based on cyclosporine microemulsion had their cyclosporine dose adjusted to the same protocol-defined C2 targets from the time of the transplant until 2 years posttransplant. The interim analyses after 1 year of enrollment is presented in this study.

RESULTS

One-year patient and graft survival were 100% and 94.8%, respectively. One-year rejection rate was 15%. C2 management of cyclosporine did not affect graft function: 1-year serum creatinine and glomerular filtration rate were 1.3+/-1 mg/mL and 71.2+/-20 mL/min/1.73 m2, respectively. C2 was the best single-point predictor of the area under the concentration curve throughout the entire follow-up, with a mean coefficient of correlation of 0.97+/-0.01.

CONCLUSIONS

C2 management of cyclosporine microemulsion therapy is effective and safe in pediatric kidney-transplant recipients given a combined immunosuppressive treatment.

Use of Neoral C2 monitoring: a European consensus

Large-scale clinical trials using C(2) monitoring of cyclosporine (CsA) microemulsion (Neoral) in renal transplant recipients have demonstrated low acute rejection rates and good tolerability with a low adverse event profile in a variety of settings: with or without routine induction therapy; in combination with mycophenolate mofetil; with standard-exposure or low-exposure Neoral; and in patients with immediate or delayed graft function. In liver transplantation, C(2) monitoring significantly reduces the severity and incidence of acute rejection compared with C(0) monitoring, without adverse consequences in terms of renal function or tolerability. Different C(2) targets are appropriate depending on adjunctive immune suppression, level of immunologic risk, CsA tolerability, risk of renal toxicity and time since transplantation. CsA absorption may increase substantially in most patients during the first 1-2 weeks post-transplant, and this should be taken into account to avoid overshooting C(2) target range. A patient with a low C(2) value may be either a low or a delayed absorber of CsA, or be a normal absorber who is receiving too low a dose of Neoral. C(2) monitoring alone is insufficient to differentiate between these types of patients, and measurement of additional timepoints is recommended. Adopting C(2) monitoring in maintenance transplant patients identifies those who are overexposed to CsA. In summary, randomized, prospective, multicenter studies and single-center trials have evaluated Neoral C(2) monitoring within a range of regimens in different organ types, providing a robust evidence base for the benefits of this sensitive monitoring technique.

C0 or C2 driven cyclosporine monitoring in long-term pediatric kidney transplant recipients: is there any threat for chronic rejection development?

The clinical management of cyclosporine has evolved greatly during the last decade thanks to the use of pharmacokinetic (PK) studies which confirmed the dose relationship between drug exposure and its biological effects. Therefore, cyclosporine PK monitoring during the early phase of the post-transplant period became essential to avoid over or underexposure to the drug thus preventing the risk of nephrotoxicity or acute rejection episodes. More recently, a simple PK determination based on cyclosporine blood concentration measured 2 h after the morning dose, has proven to be very effective for monitoring cyclosporine exposure in the early postoperative period. In this paper, the authors present a set of PK profiles obtained from a stable, long-term pediatric kidney transplant population and correlate these parameters with the risk of chronic rejection development. The study shows how cyclosporine monitoring based on the sole trough level determination misled a correct therapeutic behavior, as revealed by the PK parameters that were constantly below the therapeutic threshold in a small patient cohort who eventually developed chronic rejection. The C2 determination should be considered as the gold standard for cyclosporine monitoring in long-term pediatric recipients.

Cyclosporine A monitoring--how to account for twice and three times daily dosing

Cyclosporine A (CsA) dose-interval pharmacokinetic profiles, performed 1-4 years post-transplantation, were collected from 74 renal transplanted children. Forty patients were on three times daily dosing (t.i.d.) and 34 on twice daily dosing (b.i.d.). Regression models for prediction of area under the curve (AUC) using 1-3 concentration time points as independent variables were developed. With similar weight-adjusted single doses (mg kg(-1)) of CsA, t.i.d. dosing resulted in a trough-concentration (C0) similar to that from b.i.d. dosing, but a 30% lower 2 h post-dose concentration (C2). For b.i.d. dosing the relationship between C0 and AUC was poor (r2=0.23) and the prediction error was large (5.8+/-33.5%). For t.i.d. dosing the relationship was better (r2=0.79), but prediction error was still large (4.5+/-24.9%). For C2 relationships were similar to those for the b.i.d. (r2=0.59) and t.i.d. (r2=0.63) groups, but explained modestly the variations of AUC (prediction error=2.6+/-16.8% b.i.d., 4.8+/-23.2% t.i.d.). Both C0 and C2 are useful monitoring methods when CsA is administered t.i.d. If the aim is similar specified daily drug exposure, the target C2 should be roughly 30% smaller in t.i.d. dosing than in b.i.d. dosing and the target C0 could be similar. The prediction error of AUC can be large in individual patients when using single time-point determinations, however. The use of multiple time points reduces the variation, but is less feasible.

Results of a Three-Year Prospective Study of C2 Monitoring in Long-Term Renal Transplant Recipients Receiving Cyclosporine Microemulsion

BACKGROUND

The clinical utility of C(2) monitoring of cyclosporine A microemulsion (CsA-ME) was evaluated in a prospective study of 110 patients more than 12 months posttransplant who demonstrated stable graft function and were receiving CsA-ME and steroids.

METHODS

Patients were converted to C(2) monitoring with the CsA-ME dose adjusted to a target C(2) range of 800 to 1,000 ng/mL and followed for 40 + 11 months.

RESULTS

At the time of conversion, 57% of patients exceeded the C(2) target, 20% of patients were below the C(2) target, and 23% of patients were within the C(2) target range. The mean dose of CsA-ME decreased from 258 + 88 to 202 + 76 mg/day (P < 0.0001), and the mean C(2) level decreased from 1,052 + 292 ng/mL to 896 + 233 ng/mL (P < 0.0002). There were no episodes of rejection. At last follow-up, 7.3% of patients had developed chronic renal allograft dysfunction. Use of antihypertensive agents decreased significantly (P = 0.0004), and mean total cholesterol decreased from 6.4 + 1.3 to 5.8 + 1.1 (P = 0.0009) after adoption of C(2) monitoring.

CONCLUSION

These findings suggest that conversion of maintenance renal transplant recipients from C(0) to C(2) monitoring of CsA-ME offers the clinical benefits of better control of hypertension and dyslipidemia, with effective protection against chronic renal allograft dysfunction. A target C(2) range of 800 to 1,000 ng/mL in maintenance patients receiving CsA-ME dual therapy seems appropriate.

Two-Hour Postdose Concentration: A Reliable Marker for Cyclosporine Exposure in Adolescents With Stable Renal Transplants

In pediatric renal transplant recipients, most patients receive maintenance treatment with cyclosporine (CsA) and mycophenolate mofetil (MMF). Until now, the 2-hour postdose CsA target level for combined maintenance treatment with MMF has not been defined. This prospective pilot study evaluated the pharmacokinetics of CsA under the influence of MMF to determine a reliable single CsA concentration time that correlates with the area under the curve (AUC(0-6h)) estimates for adolescents who were additionally treated with MMF during the late posttransplant period. The study included 13 adolescents (mean posttransplantation time, 3.5 +/- 2.55 years) with stable renal transplant function (S-Crea 121 +/- 40 micromol/L). CsA pharmacokinetic absorption profiles over a 6-hour dose interval (n = 26) were evaluated for the optimal single peak concentration using the CsA concentrations predose (C0) and at 1, 2, 3, 4, and 6 hours postdose (C1-6). Whereas C2 (mean 743.2 +/- 221.8 ng/mL) was the single point with the closest correlation to AUC(0-6h) (r2 = 0.86; P < .001), C0 (mean 120.5 +/- 35.2 ng/mL) showed the weakest correlation (r2 = 0.61, P = .002). C2 appears to be an accurate predictor of CsA exposure in adolescent kidney transplant recipients under maintenance immunosuppression in combination with MMF. Average values achieved with current dosing practices cluster around the target C2 ranges recommended for adults. The data provide a foundation for initiation of prospective clinical trials to assess the long-term risk for chronic allograft dysfunction among pediatric stable renal transplant patients in combination protocols.

Pharmacokinetic advantages of two-hour post-dose cyclosporin a level for the therapeutic drug monitoring in stable Chinese kidney transplant recipients

BACKGROUND

Recent studies in Caucasian patients show that 2-hour post-dose cyclosporin A level (C2) monitoring has excellent correlation with the actual drug exposure and risk of rejection. However, the reliability of using C2 in stable Chinese renal transplant patients is unknown.

METHODS

Forty-nine stable Chinese renal transplant patients receiving microemulsion cyclosporin A (Neoral) as part of their immunosuppressive therapy were recruited. Area under the time-concentration curve (AUC) was determined from whole blood cyclosporin A level taken at 0, 1, 2, 4 and 6 h post-dose at time 0 month. Cyclosporin A levels were repeated at 0, 1 and 2 h post-dose at 1 and 2 months later to determine the intra-individual variation at these specific time points.

RESULTS

The average duration of transplantation was 77 +/- 42 months, with average daily cyclosporin dosage of 200 +/- 43 mg in two divided doses. AUC has excellent correlations with cyclosporin A level at 1 h (C1) and 2 h (C2) (r = 0.81 and 0.82 respectively, p < 0.001 for both). The correlation between AUC and trough cyclosporin A level (C0) was statistically significant but only modest (r = 0.52, p < 0.001). On the other hand, the intra-individual coefficient of variation (CVw) of C1 was significantly larger than that of C2 (34.4 +/- 24.2 vs. 15.9 +/- 8.3%, p < 0.0001).

CONCLUSION

We conclude that C2 level has favorable pharmacokinetic properties for therapeutic drug monitoring in stable Chinese transplant recipients. Both C1 and C2 have excellent correlation with AUC, but the intra-individual variability of C2 is much lower than that of C1.

C2 is superior to C0 as predictor of renal toxicity and rejection risk profile in stable heart transplant recipients

To assess whether cyclosporine A (CsA) 2-h peak (C2) is superior to trough levels (C0) for Neoral dose monitoring in heart transplantation (HT), we studied 928 C0-C2 paired determinations from 313 stable HT patients (257 male, aged 50 +/- 14 years at HT, follow-up 6.9 +/- 4 years), on a C0-based regimen. Our target C0 levels (ng/ml) were 150-400 (first 3 months), 150-300 (4-12 months), 100-250 (>12 months). Mean C0 and C2 levels were 268 +/- 80 and 1031 +/- 386, respectively (first 3 months); 230 +/- 49 and 955 +/- 239 (4-12 months); 157 +/- 53 and 745 +/- 236 (>12 months). For patients within the target C0, the corresponding C2 were 600-1500 (first 3 months), 600-1300 (4-12 months), 400-1100 (>12 months). C2 correlated with C0 (r = 0.64, P = 0.0001). C2 correlated better with CsA dose than C0 (r = 0.41, P = 0.0001 vs. r = 0.33, P = 0.0001). Between patients, CsA dose varied by a factor of 9.3; the C/dose ratio varied by a factor of 8.5 for C2 and of 15.6 for C0. Patients with higher C2 (>740) had higher severe rejection score at 2 years (P = 0.02) than patients with lower C2. This did not apply to C0. Both C2 and C0 correlated with blood urea (r = -0.18, P = 0.0001; r = -0.12, P = 0.0002) and creatinine (r = -0.19, P = 0.0004; r = -0.19, P = 0.0001 respectively). By logistic regression higher C2 (>740) was associated with higher total severe rejection score at 2 years (P = 0.006). C2 showed better correlation with CsA dose, renal function, rejection profile and less variability between patients than C0. C2 may improve CsA-based immunosuppression in HT.

Immunosuppressive drug monitoring of sirolimus and cyclosporine in pediatric patients

Sirolimus is primarily used as a rescue agent in pediatric transplant recipients, particularly in cases of cyclosporine or tacrolimus toxicity. Preliminary data indicate a higher apparent oral clearance in younger children (4-10 years of age). Various drug interactions have been described between sirolimus and drugs that are substrates/inhibitors or inducers of CYP3A and the P-glycoprotein transporter. Close monitoring of trough sirolimus blood levels is therefore recommended for pediatric transplant recipients. In de novo adult kidney transplant recipients on triple therapy with cyclosporine, corticosteroids and sirolimus, a therapeutic window of 4-12 microg/l is recommended for sirolimus trough concentrations determined by HPLC or LC/MS-MS. In maintenance adult patients after conversion to a calcineurin inhibitor-free regimen, sirolimus trough concentrations of 5-10 microg/l are proposed in combination with mycophenolate mofetil. These therapeutic ranges may also serve as a guide for pediatric renal transplant recipients. The concept of C2 monitoring still needs to be critically evaluated in pediatric patients. The crucial importance of achieving an adequate cyclosporine exposure early after transplantation has been demonstrated for adult transplant recipients. A cyclosporine concentration taken 2 h after dosing is a good surrogate marker of the AUC0-4h in adults. Various clinical studies have shown that in pediatric patients, the C2 concentration shows a substantially better correlation with cyclosporine exposure compared to the trough level (C0). In an outcome study with pediatric renal transplant recipients, it could be demonstrated that the AUC(0-4h) was a predictor of acute rejection in the first 3 weeks after transplantation, whereas C2 levels showed no significant association. Abbreviated AUC strategies may be preferable for optimization of CsA exposure in pediatric patients.

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.

Therapeutic drug monitoring of cyclosporine

Therapeutic drug monitoring of cyclosporine has been established as part of the routine clinical treatment for patients after organ transplantation. The inability to define optimal dose (maximize efficacy/minimize toxicity) has been a problem related to drug monitoring of cyclosporine. The original cyclosporine formula showed high intra-patient and inter-patient variability and low bioavailability. The microemulsion formulation of cyclosporine (Neoral) was introduced to address the absorption problems related to the original cyclosporine formulation. With the introduction of Neoral, renewed interest in methods of therapeutic drug monitoring brought us from trough monitoring (C0) to levels measured 2 hours after dosing (C2). The pharmacokinetic rationale for using C2 to monitor patients receiving Neoral has demonstrated a reduced incidence of rejection in de novo patients and improvements in safety profile in both renal and hepatic transplant recipients. Monitoring C2 levels is a more precise method for optimizing cyclosporine dosing and a better way to individualize therapy. Further data are required from prospective trials to evaluate the clinical benefits of adopting C2 monitoring in cardiac and lung transplant recipients as well as in long-term maintenance patients.

Impact of cyclosporine in the development of immunosuppressive therapy

Cyclosporine has been of great interest to the transplant community during the last 20 years. It has permitted an evolution of knowledge through the changes in its original galenic formulation of Sandimmune to Neoral, and now through the recent application of the knowledge of pharmacodynamics and pharmacokinetics to tailor drug doses to each individual. The achievements of cyclosporine are still valid and possibly will be for the next years.

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.

Clinical outcomes during the first three months posttransplant in renal allograft recipients managed by C2 monitoring of cyclosporine microemulsion

BACKGROUND

MO2ART (monitoring of 2-hr absorption in renal transplantation) is the first prospective, multicenter trial of cyclosporine (CsA) blood level 2 hr postdose (C2) monitoring in de novo kidney recipients receiving CsA microemulsion (ME) (Neoral; Novartis, Basel, Switzerland). Efficacy and safety results from the first 3 months are presented here.

METHODS

MO2ART is a 12-month, open-label, randomized study involving 296 patients. In all patients, the dose of CsA-ME was adjusted to achieve protocol-defined C2 targets of 1.6 to 2.0 microg/mL for the first month, with subsequent tapering. Randomization into two target groups occurred at 3 months. All patients received steroids and mycophenolate mofetil (89%) or azathioprine. For patients with delayed graft function, the protocol permitted reduced C2 targets and prophylactic administration of antibodies.

RESULTS

At 3 months, overall incidence of biopsy-proven acute rejection was 11.5%. Median serum creatinine was 132 micromol/L. Patient and graft survival were 96.6% and 91.2%, respectively. C2 levels greater than 1.6 microg/mL were achieved within 5 days by 60.6% of patients with immediate graft function and 19.5% of patients with delayed graft function. Prophylactic antibodies were used in 15% of the total population. Twenty-four patients (8.1%) experienced serious adverse events with a suspected relation to CsA, and 26 patients (8.8%) discontinued the study because of adverse events (n=15) or after a switch in immunosuppression after rejection episodes (n=11).

CONCLUSIONS

Patient management by C2 monitoring resulted in a low incidence of biopsy-proven acute rejection in standard risk de novo kidney recipients, 85% of whom did not receive prophylactic antibodies. CsA-ME with C2 monitoring provides excellent short-term efficacy and safety among de novo renal transplant patients.

Longitudinal evaluation of the pharmacokinetics of cyclosporin microemulsion (Neoral) in pediatric renal transplant recipients and assessment of C2 level as a marker for absorption

BACKGROUND

There are important differences in CsA pharmacokinetics between adult and pediatric patients, such that pharmacokinetic data can not necessarily be extrapolated from the adult to the pediatric setting. Research in adult renal transplant patients has shown that adequate cyclosporin exposure (AUC0-4) in the first week post-transplant is important for successful clinical outcome, and that cyclosporin concentration at 2 h post-dose (C2) provides the optimal single-time point marker for AUC0-4. Clinically, dose management based on C2 level results in a low incidence of acute rejection in the adult renal transplant population. The study reported here undertook pharmacokinetic profiling in de novo renal transplant patients over a period of 6 months and retrospectively assessed alternative monitoring strategies based on pharmacokinetic findings and clinical outcomes.

METHODS

This open-label, observational, prospective study was carried out at four UK transplant centers over a period of 6 months in pediatric de novo renal transplant recipients receiving the microemulsion formulation of cyclosporin (Neoral) according to local protocol. Twelve-hour pharmacokinetic profiles (8-16 blood samples each) were performed on days 5 and 14 and at weeks 4, 13 and 26 post-transplant.

RESULTS

Thirty-two patients were recruited (median age 10 yr, range 3-18 yr). At 6 months, patient survival was 100% and graft survival was 91%. The incidence of clinically determined acute rejection was 41% (13 of 32). Six patients discontinued Neoral before 6 months: three due to graft loss, one due to rejection, one due to renal toxicity and one due to hypertrichosis. At all time points studied, C2 correlated more closely with AUC0-4 and with AUC0-12 than did the pre-dose cyclosporin concentration (C0, or trough). Patients achieving C2 > 1.5 microg/mL by the fifth postoperative day experienced no acute rejection in the first 6 months, compared with a 50% rejection rate among patients with C2 < 1.5 microg/mL (P < 0.05). Binary logistic regression analysis showed that C2 level >1.7 microg/mL was associated with approximately 90% probability of freedom from acute rejection. Analysis of renal function across patients grouped according to cyclosporine exposure (AUC0-4, C2) showed no adverse effects of higher/increased exposure on creatinine or GFR.

CONCLUSIONS

C2 level provides a more reliable marker for CsA exposure than C0 in pediatric renal transplant recipients, and is more closely predictive of acute rejection risk. A C2 target of 1.7 microg/mL appears appropriate in this population during the immediate post-transplant period in order to maximize clinical benefit.

Comparison of cyclosporine absorption profiles over a 12-month period in stable pediatric renal transplant recipients

Evidence suggests that the pharmacokinetic (PK) profile of microemulsion- cyclosporine A (m-CsA) during the 4-hour absorption phase represents an accurate tool to estimate drug exposure. In addition, several reports suggest a close correlation between selected single CsA concentrations at 1, 2, or 3 hours post-dose (C(1), C(2), and C(3)) and the abbreviated area under the curve (AUC)(0-4) among pediatric renal transplant patients. However, it is still unclear whether these PK correlations remain stable and reliable over 12 months posttransplant. In this study, we obtained 4-hour pharmacokinetic profiles (AUC(0-4)) from stable pediatric renal transplant recipients (phase 1) with repeat measurements 12 months later (phase 2). In addition, we evaluated the optimal single sampling point that correlated with the AUC(0-4) during both phases of the study. Over 1 year there was no significant change in the AUC(0-4) of m-CsA in pediatric renal transplant recipients. The mean dose-normalized AUC(0-4) values changed by less than 2.5%, namely, 557 versus 545 ng x h/mL per unit dose, respectively. The C(1) value was the sampling point that showed the best correlation with AUC(0-4); C(0) displayed the weakest correlation. No changes in cyclosporine dosing or glomerular filtration rate estimates were observed throughout the study period. This study demonstrates the stability of drug measurements during m-CsA therapy.

A pharmacokinetic and clinical review of the potential clinical impact of using different formulations of cyclosporin A. Berlin, Germany, November 19, 2001

A meeting of 14 transplant and pharmacokinetic specialists from Europe and North America was convened in November 2001 to evaluate scientific and clinical data regarding the use of different formulations of cyclosporin A (CsA). The following consensus was achieved. (1) CsA is a critical-dose drug with a narrow therapeutic window. Clinical outcomes after transplantation are affected by the pharmacokinetic properties of CsA, particularly by its bioavailability, and by intrapatient variability in CsA exposure. (2) Standard bioequivalence criteria do not address differences in CsA pharmacokinetics between transplant recipients and healthy volunteers, or between subpopulations of transplant recipients. (3) In some circumstances, currently available formulations of CsA that meet standard bioequivalence criteria are likely to be nonequivalent with respect to pharmacokinetic characteristics. (4) The choice of CsA formulation can affect the short- and long-term clinical outcome. Currently, there is a lack of clinical comparisons between generic CsA formulations and the Neoral formulation (Novartis Pharmaceuticals Corporation, East Hanover, New Jersey). Initial retrospective data from the Collaborative Transplant Study suggest that use of generic CsA formulations may result in reduced graft survival at 1 year. (5) Management of transplant recipients by monitoring Neoral concentrations 2 hours after dosing (C(2)) reduces the incidence and severity of acute rejection compared with monitoring of trough concentrations with no increase in toxicity. C(2) monitoring has been developed based on the pharmacokinetics of Neoral only and has not been evaluated or validated for generic formulations of CsA. (6) The major costs of care after transplantation relate to the management of poor clinical outcomes and toxicity. CsA formulations with different pharmacokinetic properties may be associated with varying clinical outcomes, which would be expected to affect total health care costs. (7) The transplant physician is responsible for selecting immunosuppressive agents and formulations for his or her patients. Any switch between CsA formulations in a particular patient should take place only in a controlled setting with adequate pharmacokinetic monitoring.

Comparison of peak and trough level monitoring of cyclosporine treatment using two modern cyclosporine preparations

AIMS

Determination of the peak cyclosporine blood level instead of the trough level promises to represent an improvement in cyclosporine therapy monitoring due to better correlation with the AUC. In kidney transplant recipients we investigated whether this conclusion applies also to a new dispersion formulation of cyclosporine (Cicloral).

PATIENTS

42 stable kidney transplant recipients were converted from Sandimmun Neoral (NEO) to Cicloral (CIC) in a 1:1 dose relation.

METHODS

On the last day of NEO administration and 14 days after conversion to CIC a full 12 h cyclosporine AUC was performed using blood samples obtained prior to and at serial times after dosing. The correlations between cyclosporine levels at these time points and the AUC were determined for NEO and CIC. For each measurement, a predicted AUC was calculated by regression analysis. The prediction error for each sampling time was calculated separately for NEO and CIC.

RESULTS

The cyclosporine trough levels showed the poorest correlation with AUC for both preparations (NEO: r = 0.187 vs CIC: r = 0.554). The best correlation was observed for samples obtained at three hours after intake of either CIC (r = 0.807) or NEO (r = 0.611). The number of 2 hours measurements that lead to an unacceptable estimate from the real AUC was somewhat lower for CIC (8/40 vs 11/41 with NEO).

CONCLUSIONS

Two- or three-hour cyclosporine level monitoring with the newer cyclosporine preparation Cicloral has at least the same precision as that of the original Neoral(R). In this study, the newer preparation even showed a tendency towards superior monitoring properties.

Therapy for acute rejection in pediatric organ transplant recipients

Despite the availability of potent immunosuppressive drugs, rejection after organ transplantation in children remains a serious concern, and may lead to significant morbidity, graft loss, and death of the patient. Acute graft rejection in pediatric recipients is first treated with methylprednisolone pulses, followed by progressive taper of corticosteroid doses. After control of the rejection episode, baseline immunosuppression has to be adjusted and closely monitored since rejection (especially late episodes, occurring more than 6 months after transplantation) may be due to a lack of compliance or sub-therapeutic drug concentrations. The management of corticosteroid resistant rejection is not standardized, and depends on the transplanted organ and previous immunosuppressive regimen. In patients experiencing corticosteroid resistant acute rejection while on a cyclosporine-based immunosuppressive regimen, cyclosporine is generally changed to tacrolimus. In case of tacrolimus-based immunosuppression, tacrolimus blood levels may be increased, and/or mycophenolate mofetil (which nowadays tends to replace azathioprine) or sirolimus may be added, although pharmacodynamic data and clinical studies with these agents are still scarce in pediatric recipients. The use of antithymocyte globulins or monoclonal anti-CD3 antibodies, muromonab CD3 (OKT3) is hampered by numerous adverse effects, including a significant risk of over-immunosuppression. These therapies are nowadays indicated in very selected cases. Other treatments such as plasmapheresis and high dose immunoglobulins may be useful in difficult cases. In patients with refractory rejection despite therapeutic escalation, the risks of over-immunosuppression, including opportunistic infections and malignancies (especially the Epstein-Barr virus related post-transplant lymphoproliferative disease) have to be balanced with the consequences of graft loss due to rejection. Detransplantation or retransplantation may, in some instances, be preferable to severe infectious or tumoral complications.

Neoral monitoring 2 hours post-dose and the pediatric transplant patient

Cyclosporin A therapy has evolved greatly over the past 25 years of clinical experience. Sophisticated studies of CsA pharmacokinetics and pharmacodynamics have led to a better understanding of the relationship between dose response and biological effect. It has become apparent that achieving target drug exposure is necessary for optimal clinical outcomes. Monitoring dose response has become a key aspect of immunosuppressive management. This review presents the information available supporting cyclosporin drug concentration drawn two hours post dose (C-2) in children who have been transplanted as the best single indicator of CsA exposure. Further studies evaluating the clinical benefit of achieving C-2 targets in children are indicated.

Immunosuppressive therapy for paediatric transplant patients: pharmacokinetic considerations

Immunosuppressive therapy in paediatric transplant recipients is changing as a consequence of the increasing number of available immunosuppressive agents. Generic and other new formulations are now emerging onto the market, clinical experience is growing, and it is expected that clinicians should tailor immunosuppressive protocols to individual patients by optimising dosages and drugs according to the maturation and clinical status of the child. Most information about the clinical pharmacokinetics of immunosuppressive drugs in paediatrics is centred on cyclosporin, tacrolimus and mycophenolate mofetil in renal and liver transplant recipients; data regarding other immunosuppressants and transplant types are limited. Although the clinical pharmacokinetics of these drugs in paediatric transplant recipients are still under investigation, it is evident that the pharmacokinetic parameters observed in adults may not be applicable to children, especially in younger age groups. In general, patients younger than 5 years old show higher clearance rates irrespective of the organ transplanted or drug used. Another important factor that frequently affects clearance in this patient population is the post-transplant time. In accordance with these findings, and in contrast with the usual under-dosage in children, the need for higher dosages in younger recipients and during the early post-transplant period seems evident. To achieve the best compromise between prevention of rejection and toxicity, dosage individualisation is required and this can be achieved through therapeutic drug monitoring (TDM). This approach is particularly useful to ensure the cost-effective management of paediatric transplant recipients in whom the pharmacokinetic behaviour, target concentrations for clinical use and optimal dosage strategies of a particular drug may not yet be well defined. Although TDM may be a tool for improving immunosuppressive therapy, there is little information concerning its positive contribution to clinical events, including outcomes, for paediatric patients. Substantial information to support the use of TDM exists for cyclosporin and, to a lesser extent, for tacrolimus, but a diversity of options affects their implementation in the clinical setting. The role of TDM in therapy with mycophenolate mofetil and sirolimus has yet to be defined regarding both methods and clinical indications. Pharmacodynamic monitoring appears more suited to other immunosuppressants such as azathioprine, corticosteroids and monoclonal or polyclonal antibodies. If coupled with pharmacokinetic measurements, such monitoring would allow earlier and more precise optimisation of therapy. Very few population pharmacokinetic studies have been carried out in paediatric transplant patients. This type of study is needed so that techniques such as Bayesian forecasting can be applied to optimise immunosuppressive therapy in paediatric transplant patients.

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.

Effect of grapefruit juice on cyclosporin A pharmacokinetics in pediatric renal transplant patients

Cyclosporin A (CsA) is an important immunosuppressant that is prone to numerous drug interactions. Grapefruit juice has been investigated, as a possible adjunct to CsA dosing in adult renal transplant recipients, to decrease CsA metabolism and reduce dosages. This study investigated this combination in pediatric renal transplant patients. Six stable pediatric renal transplant patients were entered into an open-label, four-period cross-over study in which patients were given their current CsA dose as either an oral solution (CsA-Sol) or a microemulsion (CsA-ME). In addition, drugs were administered concurrently with water or grapefruit juice. Steady-state pharmacokinetic profiles were taken during each of the four periods. Following the concurrent administration of grapefruit juice, CsA whole-blood 12-h trough levels were significantly increased during CsA-Sol dosing. Furthermore, the CsA elimination rate constant was significantly reduced during the same period. After CsA-ME dosing, no differences in CsA pharmacokinetics were found between concurrent water or grapefruit ingestion. Grapefruit juice co-administration reduced the production of CsA metabolites, AM1 and AM9, during CsA-Sol dosing. No changes in CsA metabolite production were found when patients were given CsA-ME with grapefruit juice as compared with water. Hence, alterations in CsA absorption and elimination occur with concurrent grapefruit juice ingestion when stable pediatric renal transplant patients are taking the oral CsA solution, but not the microemulsion formulation. These changes may be mediated by alterations in intestinal or hepatic metabolism, or drug absorption. The effect of grapefruit juice on CsA absorption is not readily predictable in these patients.

Impact of absorption profiling on efficacy and safety of cyclosporin therapy in transplant recipients

The optimisation of cyclosporin therapy remains a challenge because of the very narrow therapeutic window and the highly variable pharmacokinetics of the drug. Therefore, there has been a concerted effort in the clinical transplant community to explore and test cyclosporin monitoring tools and techniques that will allow blood concentrations of cyclosporin to be maintained within the narrow therapeutic window in order to maximise efficacy and minimise toxicity. Absorption profiling is a simple and accurate technique for adjusting dosages of cyclosporin microemulsion that utilises an estimation of the rate and extent of cyclosporin absorption in order to optimise immunosuppression in the individual patient. Two estimation tools in particular are an abbreviated area under the concentration-time curve (AUC) for the first 4 hours postdose and a single sampling point at 2 hours postdose. These 2 monitoring strategies have not only been validated as an accurate estimation of cyclosporin bioavailability but have been demonstrated to significantly improve clinical outcomes in patients compared with traditional trough concentration monitoring. The evidence presented in this review demonstrates that absorption profiling results in the following clinical benefits compared with trough concentration monitoring: (i) reduced incidence of acute rejection; (ii) reduced severity of rejection episodes; (iii) reduced nephrotoxicity; and (iv) a rational basis for dosage adjustments. The optimisation of immunosuppressive therapy continues to be a major priority in the management of the organ transplant recipient. Absorption profiling is a sensitive and practical approach for optimising the dosage of cyclosporin microemulsion, and can further extend the benefits of cyclosporin immunosuppression in the individual patient.