CsA Clearance Research Articles

Population pharmacokinetics of ciclosporin in allogeneic hematopoietic stem cell transplant recipients: C-reactive protein as a novel covariate for clearance.

Ciclosporin (CsA), a potent immunosuppressive agent used to prevent graft-versus-host disease in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients, is characterized by large inter-individual variability and a narrow therapeutic range. The aim of this study was to develop a population pharmacokinetic model for CsA in Chinese allo-HSCT recipients and to identify covariates influencing CsA pharmacokinetics. A total of 758 retrospective drug monitoring data points were collected after intravenous infusion or oral administration of CsA from 59 patients. Population pharmacokinetic analysis was performed using nonlinear mixed effects modelling expressed by differential equations. Monte Carlo simulation was applied to optimize dosage regimens. The final model was validated using bootstrap and normalized prediction distribution errors. The results showed that the daily CsA dose, haematocrit, total bile acid, C-reactive protein (CRP) and co-administration of triazole antifungal agent were identified as significant covariates for clearance (CL) of CsA. The typical value of CL was 19.8L/h with an inter-individual variability of 13.1%. The volume of distribution was 1340L. Bioavailability was 67.2% with an inter-individual variability of 8.5%. Dosing simulation based on the developed model indicated that patients with high CRP concentration required a higher daily dose to attain the therapeutic trough concentration. The influence of CRP ultimately on the therapy outcome of CsA is not clear, which needs further study. CRP concentration was identified as a novel marker associated with CsA pharmacokinetics, which should be considered when determining the appropriate dosage of CsA in allo-HSCT recipients.

Rationale for Monitoring Cyclosporine Concentration at 2 Hours After Administration in Infants Posttransplantation

Therapeutic drug monitoring is critical to avoid overimmunosuppression or underimmunosuppression in young pediatric transplant recipients. The objective of this study was to examine cyclosporine (CsA) trough (C0) and 2-hour post-dose (C2) concentrations in the early period after liver transplantation (OLT) to determine whether CsA C2 monitoring is justified. Seventeen infants younger than 2 years treated with CsA (Neoral) were monitored at C0. The biopsy-proved acute rejection rate was 65% at 3 months post-OLT. No correlation was observed between values at C0 and C2. Poor absorption of CsA was observed in most infants during the first 2 weeks post-OLT, as well as interindividual variability in CsA clearance. Exposure to CsA could not be estimated using either C0 or C2 determinations in the early post-OLT period. As a marker of poor absorption, C2 is useful but does not indicate delayed or rapid clearance of drug without simultaneous measurement of concentration at C0. We suggest the use of both C0 and C2 monitoring, or AUC monitoring on an individual basis during at least the first 2 weeks post-OLT.

Population Pharmacokinetic Study of Cyclosporine in Patients With Nephrotic Syndrome

Cyclosporine (CsA) is widely used in the treatment of nephrotic syndrome (NS). A population pharmacokinetic (PopPK) model was developed using trough blood CsA concentration data from 106 patients with NS. The pharmacokinetic analysis was performed using NONMEM with 1-compartment linear model and first-order elimination. Proportional and additive error models were used to describe the interindividual and intraindividual variabilities, respectively. Body weight (WT), serum albumin level (ALB), and combination therapy with rifampicin were found to be the most significant covariates explaining the variability of the apparent clearance (CL/F) of CsA among patients. The final model was as follows: TVCL/F=34.1x(WT/67.6)(1.08)x(1+RFAx0.67)x(1-ALBx0.0088); TVV/F=3.5xWT; Ka=1.28 fixed; where RFA=1 with concurrent rifampicin use and 0 otherwise. The interindividual variabilities of CL/F and V/F were 18% and 27%, respectively. The residual error was 0.064 mg/L. The mean+/-SD of CL/F and V/F of the 106 patients were 23.5+/-7.2 L/h and 232.3+/-71.5 L, respectively. The reliability and stability of the PopPK model were confirmed by nonparametric bootstrap procedure.

Limitations of cyclosporine C2 monitoring in pediatric heart transplant recipients

Monitoring CSA levels at two h after dosing (C2) has been shown effective in providing adequate CSA-based immunosuppression in clinical trials in adult transplant recipients, but there is limited data regarding C2 monitoring in pediatric transplant recipients. Given the differences in CSA pharmacokinetics between children and adults, a cohort of stable pediatric transplant recipients was converted from monitoring CSA trough (C0) to C2 levels, to establish the clinical utility and safety of C2 monitoring. After an abbreviated AUC(0-5) to establish baseline exposure, subsequent CSA dosing was adjusted based on C2 levels. Additional evaluation included monitoring for rejection, changes in CSA dose, toxicity, serum chemistries, and infection. Twelve heart transplant recipients were enrolled, with mean age 4.8 yr (range: 0.6-14.0). All patients received microemulsified CSA (Neoral((R)); Novartis Pharmaceuticals, East Hanover, NJ, USA) twice daily. Baseline CSA dose was 5.39 +/- 2.05 mg/kg/day (mean +/- s.d.), with mean C0 = 267 +/- 112, C2 = 1065 +/- 565, and AUC(0-5) = 3817 +/- 1435. Only seven participants showed clear CSA peak levels at two h, with five exhibiting delayed peaks at three to five h post-dose. These seven participants completed 48 wk of study, with mean CSA dose decreasing to 4.55 +/- 3.61 mg/kg/day, maintaining mean C2 599 +/- 211 (vs. target C2 = 800). No significant change in serum creatinine was observed, although GFR increased from 76.9 to 107.6 mL/min/1.73 m(2) (p = 0.11). Five patients failed to achieve target C2 levels (>800) during the first four wk, despite comparable AUC values, and were maintained on trough monitoring (C0). Mean systolic and diastolic blood pressures fell slightly, three minor infections were noted during the study period, and one episode of acute rejection occurred, despite stable CSA dosing. Nearly 50% of stable pediatric transplant recipients failed to achieve adequate peak C2 CSA levels during conversion from C0 to C2 monitoring. Age-dependent differences in CSA absorption and/or clearance pharmacokinetics may explain these findings.

Letter to the Editor

A population pharmacokinetic analysis of cyclosporine (CsA) was performed, and the influence of covariates on CsA oral clearance and relative bioavailability was investigated. Data from 48 recipients of heart-lung (n = 21) or single (n = 18) or double (n = 9) lung transplant were included in the study. Patients received oral CsA as either a conventional formulation (Sandimmune) or a microemulsion (Neoral). Steady-state CsA concentrations were measured before and at approximately 2 and 6 hours after the morning dose of CsA at the end of weeks 1, 2, 3, 4, 13, 26, 39, and 52 posttransplantation. A total of 1004 CsA concentration observations were analyzed using mixed effects-modeling (NONMEM). A 1-compartment pharmacokinetic model and first-order oral absorption were used to fit the data. The absorption rate constants were fixed at 0.25 L/h for Sandimmune and 1.35 L/h for Neoral formulations. Oral clearance (CL/F) was estimated to be 22.1 L/h (95% confidence intervals [CI] 19.5-24.7 L/h). Itraconazole (ITRA), cystic fibrosis (CF), and weight (WT) were identified as significant covariates for CL/F according to the final model: CL/F = 22.1 - 11.3 x ITRA + 23.5 x CF + 0.129 x (WT - 58.7) L/h; where ITRA = 1 if the patient was taking concomitant itraconazole, otherwise 0; CF = 1 if the patient had cystic fibrosis, otherwise CF = 0; and WT is patient weight in kilograms. The relative oral bioavailability of Sandimmune to Neoral was 0.82. The bioavailability of both preparations increased during the first month posttransplantation. Age, gender, and type of transplant (single, double, or heart-lung) were not identified as significant covariates for CsA clearance. The population pharmacokinetic model developed identified some sources of variability in CsA pharmacokinetics; however, an appreciable degree of variability is still present in this patient population.

Evolution of the absorption profile of cyclosporine A in renal transplant recipients: a longitudinal study of the de novo and maintenance phases

Therapeutic drug monitoring for cyclosporine microemulsion (CsA-ME) is often performed using either trough levels (C0) or levels at 2 h post-dose (C2). This analysis assessed changes in C0 and C2 and their relationship to CsA-ME dose over time post-transplant in renal transplant patients. Data were obtained from MO2ART, a prospective multicentre trial in which CsA-ME dose was adjusted based on C2 level. All 98 patients in whom C0 and C2 were available at day 5, month 3 and month 12 were included, out of 234 who completed the 12 month study. Normalized dose (ND) of CsA-ME, defined as dose per kilogram body weight, was calculated, together with C0/ND, C2/ND and C2/C0. C0/ND and C2/ND both increased between day 5 and month 3: C0/ND from 33+/-15 to 53+/-24 (ng/ml)/(mg/kg) and C2/ND from 161+/-64 to 248+/-80 (ng/ml)/(mg/kg). Between month 3 and month 12, C2/ND remained stable but C0/ND decreased to 42+/-20 (ng/ml)/(mg/kg) while the C2/C0 ratio increased from 5.2+/-1.9 to 6.5+/-2.3, indicating an acceleration of drug elimination. The inter-individual coefficient of variation was higher for C0/ND than for C2/ND at 3 months (45 vs 32%, P<0.05) and at 12 months (48 vs 31%, P<0.01). CsA clearance accelerates between months 3 and 12 post-transplant, resulting in lower C0 levels for a given exposure (as measured by C2). As a consequence, C0 monitoring may progressively underestimate CsA exposure during the first year post-transplant. C2 monitoring contributes to improved individualized CsA-ME treatment in both the de novo phase and beyond month 3.

POPULATION PHARMACOKINETICS OF CYCLOSPORINE IN CLINICAL RENAL TRANSPLANT PATIENTS

Population pharmacokinetics of cyclosporine (CsA) in clinical renal transplant patients has been reported in the present study. A total of 2,548 retrospective drug monitoring data points were collected from 120 renal transplant patients receiving CsA. Population modeling was performed using the NONMEM (nonlinear mixed-effect modeling) program, using a one-compartment model with first-order absorption and elimination. The final regression model for CsA clearance (CL/F) with the influence of six significant covariates, comprising postoperative days (POD), total bilirubin level (TBIL, micromolar concentration), current body weight (CBW, kilograms), age (years), concurrent metabolic inhibitors of cyclosporine (INHI), and hematocrit (HCT, percentage), has been established and expressed as CL/F=28.5 -- 1.24 . POD -- 0.252 . (TBIL -- 11)+0.188 . (CBW -- 58) --0.191 . (Age -- 42) -- 2.45 . INHI -- 0.212 . (HCT-- 28) (liters per hour). The values in parentheses represent the median level for each of the corresponding covariates. The population estimates for CL/F (28.5 l/h), V/F (volume of distribution, 133 l), and interpatient variability (CV%=19.7%) for CL/F were achieved, respectively. The population model was further validated by internal and external approaches, and was demonstrated to be effective and stable. Moreover, simulation was conducted to facilitate the individualized treatment based on patient information and the final model.

Preprandial C2 monitoring of cyclosporine treatment in children with nephrotic syndrome

Sirs, We read with great interest the article by Rinaldi et al. [1] regarding cyclosporin (CsA) monitoring by use of abbreviated area under the curve (AUC) in nephrotic syndrome (NS). Although dose monitoring based on CsA trough levels (C0) has been widely used, it has been reported to be poor predictor of clinical outcome [2]. Recently, monitoring of 2-h post-dose CsA levels (C2) has been reported to be useful in adult transplant recipients [3], although the best way to monitor the blood levels remains unclear in children. Rinaldi et al. stated that mean CsA blood levels correlate with AUC better than C0 or C2 levels [1]. Though abbreviated AUC using this measure may be helpful in children with long-lasting NS and result in a low incidence and less toxicity, it is impractical to collect several blood samples and is more expensive. We are currently investigating the usefulness of single measurement of blood concentration 2 h after preprandial CsA (Neoral oral formulation, Novartis) administration. So far, 12 children (mean age 9.6 years) with steroiddependent (N=8) or steroid-resistant NS (N=4) in remission were enrolled in the study. Renal biopsy was performed on all patients before commencement of CsA treatment; this revealed minimal change disease in 11, focal segmental glomerulosclerosis in 1. CsA level had been initially monitored by C0 level for 6 months (C0 period) and subsequently converted to C2 level (6 months: C2 period). Oral dose of CsA was started from 2.5–5 mg kg 1 daily in two divided doses and was adjusted to target levels: C0 of 50–100 ng mL 1 by postprandial administration and C2 of 400–600 ng mL 1 by preprandial administration. It is postulated that high variability of intra-individual or inter-individual CsA blood level during the absorption phase [4] results in low reproducibility. Therefore, we used preprandial C2 level for monitoring because this may improve the variability [5]. With regard to steroids during the study period, predonisone (PSL) was used only until achieving remission when patients relapsed: then it was tapered off over 3 to 6 months. Clinical and laboratory data during the study period are summarized in Table 1: whereas the average number of relapses was not significantly different between the C0 period and the C2 period, the mean dose of CsA in the C2 period was significantly lower than that in C0 period (P<0.01) and the mean dose of PSL in the C2 period was nearly two-thirds that in C0 period. Because clearance of CsA is more rapid in children than in adults [6], C0 might be lower than the corresponding AUC, resulting in a larger dose of CsA. Taken together, we believe that CsA monitoring using the preprandial C2 level is closer to the AUC than that using C0, and is more simple and less expensive than that of mean concentrations. S. Fujinaga ()) · M. Takada · Y. Ohtomo · S. Akashi Division of Nephrology, Saitama Children’s Medical Center, Shuichiro 2100, Magome Iwatsuki City, Saitama 339, 8551 Iwatsuki, Japan e-mail: f_shuich@d2.dion.ne.jp Tel.: +81-48-758-1811 Fax: +81-48-758-1818

Population Pharmacokinetics of Cyclosporine in Cardiopulmonary Transplant Recipients

A population pharmacokinetic analysis of cyclosporine (CsA) was performed, and the influence of covariates on CsA oral clearance and relative bioavailability was investigated. Data from 48 recipients of heart-lung (n = 21) or single (n = 18) or double (n = 9) lung transplant were included in the study. Patients received oral CsA as either a conventional formulation (Sandimmune) or a microemulsion (Neoral). Steady-state CsA concentrations were measured before and at approximately 2 and 6 hours after the morning dose of CsA at the end of weeks 1, 2, 3, 4, 13, 26, 39, and 52 posttransplantation. A total of 1004 CsA concentration observations were analyzed using mixed effects-modeling (NONMEM). A 1-compartment pharmacokinetic model and first-order oral absorption were used to fit the data. The absorption rate constants were fixed at 0.25 L/h for Sandimmune and 1.35 L/h for Neoral formulations. Oral clearance (CL/F) was estimated to be 22.1 L/h (95% confidence intervals [CI] 19.5-24.7 L/h). Itraconazole (ITRA), cystic fibrosis (CF), and weight (WT) were identified as significant covariates for CL/F according to the final model: CL/F = 22.1 - 11.3 x ITRA + 23.5 x CF + 0.129 x (WT - 58.7) L/h; where ITRA = 1 if the patient was taking concomitant itraconazole, otherwise 0; CF = 1 if the patient had cystic fibrosis, otherwise CF = 0; and WT is patient weight in kilograms. The relative oral bioavailability of Sandimmune to Neoral was 0.82. The bioavailability of both preparations increased during the first month posttransplantation. Age, gender, and type of transplant (single, double, or heart-lung) were not identified as significant covariates for CsA clearance. The population pharmacokinetic model developed identified some sources of variability in CsA pharmacokinetics; however, an appreciable degree of variability is still present in this patient population.

Cyclosporin immunosuppression of sheep: pharmacokinetics and allograft survival

A chronically immunosuppressed sheep model was established using a regimen of cyclosporin A (CsA; 2–3 mg/kg twice daily) and ketoconazole (10 mg/kg twice daily). Blood CsA concentrations reached a steady-state after 17 days of treatment. The clearance of CsA decreased from a mean (95% CI) of 9.47 (6.2–12.7) ml/min/kg after a single (first) dose (3 mg/kg i.v.) to 1.62 (1.38–1.86) ml/min/kg after 18 days of CsA (3 mg/kg i.v. twice daily) co-administration with ketoconazole. These data indicated that the combination of CsA and ketoconazole could be used to give stable high concentrations of CsA in the sheep. Using this regimen in the sheep, the long-term survival of skin allografts was monitored as an indicator of effective immunosuppression. CsA in blood was measured daily and CsA dose adjusted to various target concentration ranges. Provided that the trough concentration of blood CsA was maintained between 1500–2500 mg/l, long-term healthy skin allografts were maintained on the sheep without significant adverse effects on haematological or biochemical parameters.

A Urine Metabolic Ratio of Dextromethorphan and 3‐Methoxymorphinan as a Probe for CYP3A Activity and Prediction of Cyclosporine Clearance in Healthy Volunteers

Dextromethorphan (DM) is metabolized in the body to dextrophan (DT) and 3-methoxymorphinan (3-MM) by cytochrome P450 (CYP) 2D6 and 3A4, respectively, and cyclosporine (CsA) is a known substrate of CYP3A4. We attempted to determine if the urine metabolic ratio of DM:3-MM at various time intervals during 24 hours is predictive of CsA clearance in 11 healthy volunteers. Each subject took DM 30 mg orally, and serial urine samples were collected at 0-4, 4, and 4-24, and 0-24 hours. Subjects then were randomly assigned to receive either oral microemulsion CsA 5 mg/kg or intravenous CsA 1.5 mg/kg in a crossover fashion in a two-sequence pharmacokinetic study with a wash-out period of at least 7 days. A total of 17 blood samples were collected from each subject in the CsA pharmacokinetic study over 24 hours. Urinary DM, DT, and 3-MM were quantified by high-performance liquid chromatography (HPLC) with a fluorescence detector, and blood CsA concentrations were analyzed by HPLC with ultraviolet detection. All subjects were extensive metabolizers of CYP2D6 as determined by metabolic ratios of DM:DT (mean+/-SD 0.0255+/-0.048). There was no correlation between CYP2D6 and CYP3A4 (p=0.38). The metabolic ratios of DM:3-MM in any urine samples during the 24-hour collection period did not predict CsA pharmacokinetics, although the 0-24 hour sample had an unexpected positive correlation with CsA clearance (r2 = 0.38, p<0.0001). The correlation was similar for metabolic ratios of DM:3-MM with intravenous CsA clearance (r2 = 0.5, p<0.0001). Metabolic ratios of DM:3-MM based on 24-hour cumulative urine collection did not appear to have clinical utility in predicting CYP3A activity measured by CsA clearance.

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 posttransplant 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/bioavailability; 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.

On the intraindividual variability and chronobiology of cyclosporine pharmacokinetics in renal transplantation.

The intraindividual variability and circadian variation of oral cyclosporine (CsA) pharmacokinetics were studied over 24 h in 18 renal transplant recipients at steady state, and in 10 of the patients during a second 24 h period. The absolute percentage intraindividual difference in daytime AUC (0-12 h) ranged from 2% to 54% (mean 30%), and the corresponding variability in nighttime AUC (0-12 h) ranged from 5% to 80% (mean 34%). The pharmacokinetic variables t1/2, tmax and Cmax were more variable than the AUC (0-12 h) both during the day and at night. The evening trough level was significantly lower than the morning trough level; 185 ng.ml-1 versus 223 ng.ml-1. This, together with a significantly longer t1/2 in the night than the day, suggested circadian variability in the pharmacokinetics of CsA. In a separate retrospective study in 162 renal transplant recipients given CsA by constant intravenous infusion, repeated CsA blood concentration measurements at steady state showed lower concentrations during the day than the night, suggesting higher CsA clearance during daytime. It is concluded that CsA pharmacokinetics in renal transplant recipients, besides the well-known interindividual variability, also displays large intraindividual variability as well as circadian variation. Our findings further emphasize the necessity and difficulty of pharmacological monitoring in the clinical use of CsA in organ transplantation.

The kinetics of cyclosporine and its metabolites in bone marrow transplant patients.

1. The pharmacokinetics of cyclosporine (CsA) and the time course of CsA metabolites were studied in five bone marrow transplant patients after intravenous (i.v.) administration on two separate occasions and once after oral CsA administration. 2. Cyclosporine and cyclosporine metabolites were measured in whole blood by h.p.l.c. 3. Cyclosporine clearance after i.v. administration decreased from 3.9 +/- 1.7 ml min-1 kg-1 to 2.0 +/- 0.6 ml min-1 kg-1 after 14 days of treatment. The mean +/- s.d. absolute oral bioavailability of cyclosporine was 17 +/- 11%. 4. Hydroxylated CsA (M-17) was the major metabolite in blood. There were no significant differences in the mean metabolite/CsA AUC ratios between the first and second i.v. studies. 5. After oral administration, the metabolite to CsA AUC ratios were higher for most metabolites compared to those observed in the second i.v. study, suggesting a contribution of intestinal metabolism to the clearance of CsA.

EVALUATION OF AMPHOTERICIN B—CYCLOSPORINE INTERACTION IN THE RAT

Although a significant interaction between cyclosporine and amphotericin-B (AmpB) has been observed clinically, these findings have not been duplicated in animal studies. A total of 64 male albino rats were used in single- and multiple-dose experiments with AmpB and CsA in the absence or presence of systemic Candida infection. No significant differences in glomerular filtration rate were found in rats given single i.v. doses of AmpB 1 mg/kg compared with AmpB and CsA. Furthermore, rats given i.p. AmpB 1 mg/kg and CsA 10 mg/kg daily for 10 days showed no significant differences in GFR compared with animals given CsA alone. Morphology and CsA whole-blood pharmacokinetics were not different between groups administered single-dose CsA, AmpB, or the combination; similarities also existed with multiple-dose studies. In an attempt to mimic the clinical setting, 2 groups of rats were administered i.p. CsA 10 mg/kg/day for 10 days followed by inoculation of Candida albicans. After 48 hr, a single i.v. dose of AmpB 1.0 mg/kg was associated with a 33% decline in GFR compared with those given sterile water (P less than 0.05). Systemic clearance of CsA was markedly reduced in candidiasis rats administered AmpB compared with controls given sterile water. A significant reduction in renal Candida colony-forming units was found in rats given CsA and AmpB compared with those administered CsA alone. These data suggest that the presence of systemic Candida highlights the interaction of CsA and AmpB in the rat model.

Pharmacokinetics of two Alternative Dosage Forms for Cyclosporine: Liposomes and Intralipid

Cyclosporine (CsA), commercially available as iv or oral Sandimmune, is a potent immunosuppressant which can induce dose-related nephrotoxocity. In addition, the iv product contains a solubilizing agent, Cremophore EL, which in itself is reported to be nephrotoxic and can induce, in sensitized patients, anaphylactic reactions. Solubilization of CsA with liposomes or lipid emulsions could provide a suitable alternative dosage form for iv administration. With this in mind, male New Zealand white rabbits were given iv CsA (10 mg/kg) in three different dosage forms: (1) CsA:liposomes; (2) CsA:Intralipid (soybean oil and phospholipids); and (3) the commercially available Sandimmune (cyclosporine). The CsA concentration in whole blood samples was analyzed by HPLC. The terminal disposition half-life of CsA (t1/2β) ranged from 400 to 475 min and was not statistically different among the three groups. However, the distribution characteristics of CsA changed dramatically depending on the dosage form. The volume of distribution of CsA at steady state (Vdss) in Sandimmune was 2.7 ± 0.2 L/kg and was significantly lower than that of either Intralipid (10.6 ± 2.7 L/kg) or liposomes (7.4 ± 2.3 L/kg). A significantly lower total body clearance (TBC) of CsA also was seen for Sandimmune (12.7 ± 0.3 mL/min/kg) as compared with that of either Intralipid (24.4 ± 8.2 mL/min/kg) or liposomes (18.9 ± 3.9 mL/min/kg). Since CsA is extensively bound to lipoproteins, it is surprising that both test vehicles showed a different distribution pattern. It is speculated that in addition to the benefit of removing Cremophore EL from the product, the different distribution of CsA:liposomes or CsA:Intralipid may prove useful in altering the nephrotoxocity and immunosuppression of CsA during iv therapy.

THE EFFECT OF RENAL ISCHEMIA ON CYCLOSPORINE CLEARANCE IN RABBITS

The renal handling of cyclosporine was studied in ischemically damaged kidneys in New Zealand White rabbits and nonischemic control animals. CsA, 25 mg/kg/day, was administered intravenously for 10 days starting with the day of operation. Blood CsA (B CsA) was higher in the ischemic group compared with the controls (median: 285 micrograms/L, range 95-785 micrograms/L vs. 170 micrograms/L, range 110-185 micrograms/L, P = 0.05) on day 1 after operation. B CsA dropped rapidly to a level equivalent to the controls by day 4 (median: 105 micrograms/L, range 60-280 micrograms/L vs. 195 micrograms/L, range 70-215 micrograms/L, P = NS). Median CsA clearance (C CsA) as a percentage of creatinine clearance (C Cr) was some ten-fold greater in the ischemic animals (6.32%, range 2.93-18.41% vs. 0.55%, range 0.13-0.78%, P less than 0.001) on day 1. The ratio gradually declined, approaching the value in controls by day 10 (0.86%, range 0.24-7.21% vs. 0.23%, range 0.16-0.73%, P = 0.05). The data suggest that renal impairment has an important effect on CsA blood levels. In the clinical situation this may be of particular importance during both oliguria and the recovery from acute tubular necrosis.

Bayesian Estimation of Cyclosporine Clearance in Bone Marrow Graft

The dosage regimen of cyclosporine (CsA) can be individualized in patients by means of a test dose (TD) method in the few days before bone marrow graft. To simplify the test dosing protocol, we used a Bayesian estimation (BE) of CsA clearance requiring population data and partial kinetic information for a given patient. In the first part, 42 patients, aged 11-47 years, were given a 2-h infusion of CsA (4 mg.kg-1). CsA concentrations were determined in several blood samples. The obtained concentration-time curves were fitted according to a three-compartment model. Maximum likelihood estimation (MLE) allowed CsA determination of pharmacokinetic parameters. Early population parameters of CsA were determined using 22 TD by a two-stage method. In the remaining 20 patients, individual pharmacokinetic parameters were also computed by BE procedure, taking into account the above determined population parameters and CsA concentration determinations from three blood samples drawn at 5 and 30 min and 3 h after the end of TD infusion. In the second part, 16 patients were used to evaluate performance of BE in directly predicting target concentration values. Finally, early population characteristics were updated on the basis of 42 patients. Statistical comparisons between MLE and BE estimates of CsA clearance and between concentrations predicted after BE and those experimentally obtained showed that three blood CsA determinations allowed accurate clearance estimation and target concentration predictions. The method presented here can be used to calculate an individual CsA dosage regimen in real time, thus improving patient comfort.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum Cyclosporine Kinetic Profile. Failure to Correlate with Nephrotoxicity or Rejection Episodes Following Sequential Immunotherapy for Renal Transplantation

Cyclosporine (CsA) level monitoring in renal transplant recipients has been thought to aid in separating clinical episodes of nephrotoxicity from rejection. Twenty-four-hour CsA pharmacodynamic profiles were obtained from 85 consecutive primary renal transplant recipients in the immediate peritransplant period in order to determine the value of this test in predicting subsequent episodes of nephrotoxicity or rejection. All patients were treated with sequential antilymphoblast globulin/CsA following transplantation. Serum samples from each recipient were analyzed for CsA levels estimated by radioimmunoassay (RIA) four days after initiation of a daily single oral CsA dose (10 mg/kg/day). A total of 52 episodes of rejection and 303 episodes of nephrotoxicity occurring within the first six months posttransplant were correlated with selected parameters from the immediate posttransplant CsA kinetic profile. For each profile these parameters were maximum CsA level, time to maximum CsA level, minimum CsA level, 95% clearance time of CsA, and total CsA accumulation and clearance during the 24 hr following ingestion of CsA. No significant correlation was found between any of these parameters and either the incidence or frequency of rejection or nephrotoxic episodes, as determined by least-squares linear regression analysis. Furthermore, following a single oral dose of CsA (10 mg/kg/day), no correlation could be found between the dose and the absorption, accumulation, metabolism, and clearance of the drug. In conclusion, maximum CsA level, time to maximum CsA level, minimum CsA level, 95% clearance time of CsA, and total CsA accumulation and clearance measured from CsA kinetic profiles cannot be correlated with or predict the incidence of rejection or nephrotoxic episodes that subsequently occur during the first six months following renal transplantation.

SERUM CYCLOSPORINE KINETIC PROFILE

Cyclosporine (CsA) level monitoring in renal transplant recipients has been thought to aid in separating clinical episodes of nephrotoxicity from rejection. Twenty-four-hour CsA pharmacodynamic profiles were obtained from 85 consecutive primary renal transplant recipients in the immediate peritransplant period in order to determine the value of this test in predicting subsequent episodes of nephrotoxicity or rejection. All patients were treated with sequential antilymphoblast globulin/CsA following transplantation. Serum samples from each recipient were analyzed for CsA levels estimated by radioimmunoassay (RIA) four days after initiation of a daily single oral CsA dose (10 mg/kg/day). A total of 52 episodes of rejection and 303 episodes of nephrotoxicity occurring within the first six months posttransplant were correlated with selected parameters from the immediate posttransplant CsA kinetic profile. For each profile these parameters were maximum CsA level, time to maximum CsA level, minimum CsA level, 95% clearance time of CsA, and total CsA accumulation and clearance during the 24 hr following ingestion of CsA. No significant correlation was found between any of these parameters and either the incidence or frequency of rejection or nephrotoxic episodes, as determined by least-squares linear regression analysis. Furthermore, following a single oral dose of CsA (10 mg/kg/day), no correlation could be found between the dose and the absorption, accumulation, metabolism, and clearance of the drug. In conclusion, maximum CsA level, time to maximum CsA level, minimum CsA level, 95% clearance time of CsA, and total CsA accumulation and clearance measured from CsA kinetic profiles cannot be correlated with or predict the incidence of rejection or nephrotoxic episodes that subsequently occur during the first six months following renal transplantation.