Maria Welsh

Demographic factors influencing cyclosporine pharmacokinetic parameters in patients with uremia: Racial differences in bioavailability

The impact of several demographic and blood biochemistry factors on the pharmacokinetics of the immunosuppressive drug cyclosporine were studied in 187 patients with uremia. All patients underwent a pharmacokinetic evaluation including a 3 mg/kg intravenous dose of cyclosporine and a 14 mg/kg oral dose of cyclosporine. Cyclosporine was analyzed by specific monoclonal radioimmunoassay on whole blood samples. Statistical analysis included univariate analyses and stepwise multiple regression analysis. Major findings were as follows: The bioavailability (F) of cyclosporine was significantly lower in black patients than in white patients (mean values of 30.9% ± 12.3% and 39.5% ± 16.5%, respectively; p < 0.001). This difference was noted both before transplant and at 1 week after kidney transplantation, at which time the corresponding mean values were 28.6% ± 15.5% and 36.1% ± 15.5%, respectively (p < 0.01). Other factors that correlated with F were serum triglyceride (positively) and blood hemoglobin concentrations (inversely). Patients with diabetes displayed a longer mean absorption time than other patients and a larger volume of distribution of cyclosporine at steady state (Vss). Other factors that correlated with Vss were serum albumin concentration and patient height. Cyclosporine clearance (CL) decreased with patient age and also with increasing concentrations of serum triglycerides and blood hemoglobin. It was lower in patients with the pretransplant diagnosis of nephrosclerosis than in patients with other diseases. Several pharmacokinetic parameters correlated with the level of substances that can potentially bind cyclosporine in the blood. Serum triglycerides correlated with maximum concentration, time to maximum concentration, F, and CL. Blood hemoglobin concentration and blood hematocrit correlated with F, CL, and intravenous mean residence time. Although several relationships were observed between demographic factors and cyclosporine pharmacokinetics, the racial difference in F is of great clinical significance and may contribute to the poorer outcome observed after kidney transplantation in black patients.

Cyclosporine monitoring in renal transplantation: area under the curve monitoring is superior to trough-level monitoring.

Summary: Trough levels (TL) of cyclosporine (CS) measured in serum by the polyclonal radioimmunoassay (SR) are useful for dissecting the etiology of clinical events, but they are a poor guide to dosage adjustments. In renal transplant patients immunosuppressed by low doses of prednisone and CS given orally, once-a-day TL (24-h) monitoring was replaced by area under the curve (AUC) monitoring, i.e., measuring the area under the concentration (SR)time curve from seven blood samples (0, 2, 4, 6, 10, 14, and 24 h) at clinical steady state, which was reached on the 3rd day after a change in the oral dose rate. The therapeutic target was an average concentration at steady state (Css av) of 200 ng/ml during the first 6 months after transplantation and 150 ng/ml thereafter. The Css av was calculated by dividing the AUC by the dosing interval (24 h). Two findings demonstrated the superiority of AUC monitoring over TL monitoring. First, in 71 paired observations AUC but not TL was significantly correlated with the dose expressed as total mg (r = 0.381, p = 0.001) or mg/kg body weight (r = 0.538, p = 0.0001). Second, after adjusting (n = 26) the oral dose rate (to achieve the therapeutic target) the absolute error (i.e., deviation from the target) in the AUC observation (15%) was significantly (p = 0.0005) smaller than in the TL observation (36%). Monitoring AUC at clinical steady state reduced the number of dosage adjustments by a factor of 3.

Challenges in cyclosporine therapy: the role of therapeutic monitoring by area under the curve monitoring.

Summary Cyclosporine has revolutionized the practice of transplantation, but its clinical application has been beclouded by a narrow therapeutic window between immunosuppressive and nephrotoxic concentrations. Marked intra-and interindividual pharmacokinetic differences preclude the use of routine dosing regimens. For example, at the intraindividual level, cyclosporine absorption improves during the first 90 days after institution of therapy. A wide range of demographic factors, namely, age, race, and concomitant drug therapy, as well as individual-specific factors produce unique pharmacokinetic behaviors in any given patient. We introduced a pharmacokinetic strategy for cyclosporine administration almost 10 years ago based on the observation that the best estimate of drug exposure was the area under the concentration-time kinetic curve (AUC) not the trough level. Early studies documented the relation between AUC and the incidence of acute rejection. Subsequent studies revealed that not only is the AUC an important predictor, but so is the consistency of drug absorption over time; namely, patients with variations >25% among AUC determinations display an increased risk of chronic rejection episodes. Therefore therapeutic drug monitoring plays an important role in the optimal care of patients under cyclosporine therapy.

The adverse impact of high cyclosporine. Clearance rates on the incidences of acute rejection and graft loss.

The influence of cyclosporine pharmacokinetic parameters on clinical events and outcome after transplantation was studied in 100 renal transplant recipients who underwent a pre-as well as posttransplant CsA pharmacokinetic evaluation. Among the patients, 30 were black and 50 were white. Black recipients had significantly lower bioavailability (F) pre-as well as posttransplantation than white recipients, the post-transplant mean F values being 25.8±9.0% and 38.1→ 16.7%, respectively (P<0.002). The posttransplant CsA clearance rate (CL) and oral clearance (clearance/bio-availability; CLoral) were significantly higher in patients who had acute rejection than in those who did not, with CL mean values of 425±141 ml/min and 359±131 ml/min, respectively (P<0.02). The initial posttransplant F was significantly lower, and the CLoral higher in patients who eventually lost their grafts than in those who did not, the mean F values being 26.5±12.8% and 38.7± 17.5%, respectively (P<0.002). Thus, several important relationships between CsA pharmacokinetic parameters and clinical events following renal transplantation were documented. The CLoral decreased during the first 3 months after transplantation (P<0.0001), but it was stable thereafter. Neither the bioavailability nor the clearance of CsA showed a correlation with administered dose. These results indicate that certain recipient groups, such as black patients, and individuals with rapid CL, may benefit from larger CsA doses and/or shorter dosage intervals, in order to compensate for these interpatient variabilities.

Risk factors for impaired wound healing in sirolimus‐treated renal transplant recipients

Abstract:  Aim:  As sirolimus has been implicated in impaired wound healing, the aim of this study was to evaluate risk factors for wound complications after renal transplantation in patients treated with this drug de novo.

The ability of pretransplant test-dose pharmacokinetic profiles to reduce early adverse events after renal transplantation

Pretransplant test-dose pharmacokinetic profiles were used to determine individual cyclosporine drug bioavailability and clearance rates in renal transplant patients. Assuming a linear relation between dose and area under the concentration curve (AUC), starting i.v. and p.o. CsA doses were computed from the test-dose results. Target values were 400 ng/ml steady-state concentration (Css) during continuous intravenous infusion, and 500 ng/ml average drug concentration (Cavss = AUC/dosing interval) after oral administration, based upon measurements with the specific monoclonal antibody 3H-tracer radioimmunoassay. The outcomes after dose individualization with a 1-(n = 32), 2-(n = 38), or 3-(n = 41) hr i.v. infusion test dose and a p.o. test dose (n = 111) were compared with 228 historical control patients who received a uniform protocol of CsA i.v. at 2.5 mg/kg/day and p.o. at 14 mg/kg/day. The observed Css after i.v. CsA was within 10% of the target concentration in 73% of recipients tested with the 3-hr protocol, a significantly greater fraction than achieved with either the uniform dose (14%), or the 1-(34%) and 2-(25%) hr protocols. Patients in the 3-hr protocol group showed reduced incidences of delayed graft function, early graft loss, and rejection episodes, and a lower mean serum creatinine value, particularly at 7 but also at 30 days posttransplantation. Administration of the predicted oral dose produced a peak concentration of greater than or equal to 700 ng/ml drug absorption in 60% of recipients at 3 days, 90% at 5 days, and 98% at 7 days. The test-dose method less effectively predicted the appropriate oral CsA dose to produce target Cssav and failed to reduce the 90-day rejection incidence. Despite its limitations with the more-complicated p.o. route, the test-dose method successfully predicts i.v. CsA doses, thereby reducing the incidence of early adverse events.

Phase I and phase II safety and efficacy trial of intercellular adhesion molecule-1 antisense oligodeoxynucleotide (ISIS 2302) for the prevention of acute allograft rejection.

Background. ISIS 2302, an antisense oligonucleotide that inhibits the expression of human intercellular adhesion molecule (ICAM)-1, was evaluated in combination with a cyclosporine (CsA)-prednisone (Pred) regimen first in a phase I safety and pharmacokinetic study and then in a phase II assessment of prophylaxis of acute rejection episodes in deceased donor renal allografts. Methods. Both phase I and phase II trials were double-blinded and placebo-controlled, including 17 stable and 39 de novo patients, respectively, in time-lagged, ascending-dose regimens. Each study compared the outcomes of 8 alternate-day intravenous infusions of four ISIS 2302 dose levels (0.05, 0.5, 1.0, or 2.0 mg/kg) versus placebo (3:1 ratio). Patients were followed for 34 days (phase I) or 6 months (phase II). All transplant patients were followed for 3 years. Results. ISIS 2302 produced no evident toxicity; a significant, dose-related increase in activated partial thromboplastin time was accompanied by a trend toward a decreased platelet count. ISIS 2302 did not alter the pharmacokinetic behavior of CsA. At 6 months, the rates of acute rejection episodes were 38.1% in the ISIS 2302 group versus 20.0% in the placebo group. Three-year graft survivals were similar. The mean creatinine values at 1, 2, and 3 years for all ISIS dose groups combined versus placebo over 3 years showed no significant differences. Conclusions. ISIS 2302 did not evoke side-effects and produced slightly improved renal function. However, in this pilot study, it did not further reduce the rate of acute rejection episodes or increase graft survival compared to a concentration-controlled CsA-Pred regimen.

Prediction of Acute Graft Rejection in Renal Transplantation: The Utility of Cyclosporine Blood Concentrations

While cyclosporine is recommended to be used only in conjunction with monitoring of its blood concentrations, the utility of these measurements in preventing treatment failure is not established. In a group of 52 patients trough levels and steady-state concentrations were monitored in serum and whole blood by specific (SP) and nonspecific (NS) assays (polyclonal radioimmunoassay, PR; fluorescence polarization immunoassay, FP; high-pressure liquid chromatography, HP). From as many as 10 determinations of trough level and steady state concentrations during the first 40 days after renal transplantation, the lowest measurement was selected. In the case of an acute rejection episode within that time period, only values until that event were considered. Trough level measurements in serum by PR/NS and by FP/NS and in whole blood by HP/SP were not significantly different between patients with and patients without rejection episodes. However, simultaneously measured steady-state values (serum/PR/NS and serum/FP/NS) were significantly lower in patients suffering from rejection (with rejection SS/ serum/PR/NS mean = 127 ng/ml, SD = 41 ng/ml; without rejection mean = 163 ng/ml, SD = 60 ng/ml; P = 0.027, t test). This difference could not be demonstrated for steady state/whole blood/HP/SP measurements. A logistic regression analysis demonstrated that the probability of rejection can be decreased by up to 40% if steady state/serum/PR/NS or steady state/serum/FP/NS values never drop below 250 ng/ml early after renal transplantation.

Pharmacokinetic strategies for cyclosporin therapy in organ transplantation

Marked interindividual variations in cyclosporin (CsA) produce disparate clinical results in organ transplant recipients. In an attempt to eliminate marked deviations of insufficient or excessive CsA concentrations consequent to the administration of uniform drug doses, test dose pharmacokinetics were performed on each potential organ transplant candidate. An intravenous 3 mg/kg test dose delivered over 3 h proved to be readily performed, namely 53% perfect studies, and relatively reliable, namely 73% of observed concentrations within 10% of the predicted values. Furthermore, the use of CsA doses predicted by pretransplant studies reduces the incidence of delayed graft function, early rejection episodes and transplant loss. The oral test dose study predicted a suitable amount of CsA to achieve sufficient gastrointestinal absorption but was less accurate than the iv prediction method: namely, 40% of observed post-transplant concentrations were within 10% of the predicted target value. Furthermore, patients who received oral doses predicted by the test dose strategy showed no improvement in the incidence of acute rejection episodes between 7 and 60 days, and only modestly improved serum creatinine values. The lower accuracy of predictions from oral test dose studies may reflect the impact of non-linear oral (as opposed to iv) drug pharmacokinetics, of variable diet, and/or of altered postoperative gastrointestinal function.