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IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL IN EARLY POST-RENAL TRANSPLANTATION PERIOD?
0022-5347/00/1631-0037/0 THE JOURNAL OF UROLOGY® Copyright © 2000 by AMERICAN UROLOGICAL ASSOCIATION, INC.®
Vol. 163, 37– 41, January 2000 Printed in U.S.A.
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL IN EARLY POST-RENAL TRANSPLANTATION PERIOD? KAMRAN MAHALATI, JOSEPH LAWEN, BRYCE KIBERD
AND
PHILIP BELITSKY
From the Kidney Transplant Program, and Departments of Urology and Medicine, Dalhousie University, Queen Elizabeth II Health Sciences Centre, Halifax, Nova Scotia, Canada
ABSTRACT
Purpose: Cyclosporine dose is traditionally based on trough blood levels. Cyclosporine trough blood level correlates poorly with acute rejection and cyclosporine nephrotoxicity after renal transplantation. We determined whether cyclosporine blood level at any other time point is superior to cyclosporine trough blood level as a predictor of acute rejection and cyclosporine nephrotoxicity. Materials and Methods: Cyclosporine blood level was measured before (trough), and 1, 2, 3 and 4 hours after the dose in 156 initial renal transplant cases 2 to 4 days after the initiation of cyclosporine micro-emulsion formula administration. The cylosporine micro-emulsion dose was based on cyclosporine trough blood level targeting 250 to 400 mg./l. Results: Regression analysis revealed that only delayed graft function (p 5 0.007) and cyclosporine blood level after 3 hours (p 5 0.008) predicted acute rejection. Mean cyclosporine trough blood level plus or minus standard error was not significantly different in patients with and without acute rejection (293 6 21 versus 294 6 11 mg./l.). Mean cyclosporine blood level after 3 hours was significantly lower in patients with acute rejection (1,156 6 90 versus 1,421 6 50, p 5 0.008). Cases were divided into tertiles at levels after 3 hours (1,100 and 1,500 mg./l.). The group in which the level after 3 hours was less than 1,100 mg./l. had the highest acute rejection rate (22 of 50 patients, 44%) and a cyclosporine nephrotoxicity rate of 13% (7 of 52 patients). The group in which the level after 3 hours was 1,100 to 1,500 mg./l. had the lowest acute rejection rate (5 of 46 patients, 11%) without increased cyclosporine nephrotoxicity (7 of 52 patients, 13%). A level after 3 hours of greater than 1,500 mg./l. was associated with a rejection rate of 15% (7 of 47 patients) but significantly higher cyclosporine nephrotoxicity (16 of 52 patients, 30%). Conclusions: Cyclosporine blood level after 3 hours in the early post-transplantation period is associated with acute rejection and cyclosporine nephrotoxicity. A cyclosporine blood level range after 3 hours of 1,100 to 1,500 mg./l. is associated with an optimal outcome. Our data suggest that cyclosporine blood level after 3 hours may represent a better method of monitoring cyclosporine micro-emulsion dose than cyclosporine trough blood level. This hypothesis must be further studied in randomized trials. KEY WORDS: kidney, cyclosporine, drug monitoring, kidney transplantation, rejection
Cyclosporine is the foundation of current immunosuppression protocols at many kidney transplant centers. Therapeutic monitoring of the drug is essential because cyclosporine has a narrow therapeutic window with serious potential side effects. Cyclosporine trough blood level, that is immediately before the next dose, has been widely used for monitoring the cyclosporine dose. Although the correlation of cyclosporine trough blood level with post-transplantation adverse clinical events, such as acute rejection and acute cyclosporine nephrotoxicity, is poor, cyclosporine trough blood level is still widely used to monitor cyclosporine treatment. Significant groups of patients have acute rejection or cyclosporine nephrotoxicity despite the maintenance of cyclosporine levels within the therapeutic range, which tends to be variable and center specific.1, 2 The area under the curve of blood cyclosporine concentration versus time is a better measurement of systemic drug exposure than cyclosporine trough blood level. The area value within week 1 after transplantation has been shown to correlate with 1-year acute rejection and graft survival after kidney transplantation.3, 4 However, therapeutic monitoring of cyclosporine based on pharmacokinetic studies and the area value has not gained popularity, largely because of the
inconvenience of multiple blood sampling during 12 hours, and the costs associated with sampling and analysis. A new galenic formulation of cyclosporine, cyclosporine micro-emulsion, is designed to overcome the absorption problems of the cyclosporine standard formulation. Cyclosporine micro-emulsion has more extensive, predictable and consistent oral absorption, less intra-subject variability, increased dose linearity with the value of the area under the curve of blood cyclosporine concentration versus time, and better but not perfect correlation of cyclosporine trough blood level and area value than the standard formulation. The hope was that cyclosporine micro-emulsion would provide more predictable drug exposure that would be reliably reflected by cyclosporine trough blood level, and result in better immunosuppression with fewer side effects.5–7 Subsequent randomized clinical trials in new kidney transplant patients showed a comparable toleration and side effect profile of the 2 cyclosporine formulations, and a lower but still significant rate of acute rejection (35% to 45%)8 –10 with cyclosporine microemulsion. The more predictable pharmacokinetic characteristics of cyclosporine micro-emulsion, and the need for a simpler and more effective way to monitor cyclosporine have led a few groups to use single post-dose cyclosporine levels for this
Accepted for publication August 13, 1999. 37
38
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
purpose. The 2 and 6-hour post-dose cyclosporine blood levels have been shown to be a useful method of monitoring cyclosporine in new and stable liver and heart transplant recipients.11–14 We examined the correlation of cyclosporine blood concentrations in the initial 4 hours after the dose measured at week 1 after transplantation with acute rejection and cyclosporine nephrotoxicity during the initial 3 months after renal transplantation. MATERIALS AND METHODS
The study population comprised 156 consecutive initial kidney transplant recipients who underwent transplantation between August 1995 and January 1998 at our institution. All patients received cyclosporine micro-emulsion based immunosuppression and none received antibody induction. Followup for the purpose of this analysis was 3 months after transplantation. Of the 156 patients 100 (64%) received cadaver, 43 (28%) nonidentical live and 13 (8%) HLA identical live donor kidneys. The latter 13 cases are included only in the analysis of cyclosporine nephrotoxicity and not acute rejection. Inpatient and outpatient records were reviewed retrospectively for episodes of acute rejection and cyclosporine nephrotoxicity within the initial 3 months after transplantation. Cyclosporine micro-emulsion dose, cyclosporine trough blood level and serum creatinine on days 1 to 14, weeks 3 to 7, and months 2 and 3 after transplantation were noted, as were patient demographics, cadaveric versus living related transplant source, panel-reactive antibody, immunosuppression regimen, HLA mismatch and delayed graft function. The diagnosis of acute rejection was confirmed by percutaneous core needle biopsy with severity classified according to the Banff criteria. Cyclosporine nephrotoxicity was defined as a greater than 30% increase in serum creatinine that was not attributable to any other identifiable cause and improved with a decrease in the cyclosporine micro-emulsion dose. Biopsies performed for renal dysfunction were free of acute rejection changes and exhibited abnormalities attributable to cyclosporine toxicity. Delayed graft function was defined as the lack of a greater than 10% spontaneous decrease in serum creatinine by day 3 postoperatively regardless of the need for dialysis. All cyclosporine blood values refer to whole blood concentrations and were determined using the monoclonal, parent compound specific, whole blood Cyclo-Trac RIA* test kit. The 13 recipients of HLA identical living related transplants were treated with prednisone and cyclosporine microemulsion only. The other 143 patients were divided into the azathioprine group—19 (13%) who received prednisone, cyclosporine micro-emulsion and azathioprine; the mycophenolate mofetil group— 61 (43%) who received prednisone, cyclosporine micro-emulsion and mycophenolate mofetil, and the rapamycin group— 63 (44%) who received prednisone, cyclosporine micro-emulsion and 5 or 2 mg. rapamycin or placebo in a 2:2:1 ratio as part of a randomized double-blind study. Cyclosporine was administered for the initial 1 to 3 days after transplantation by continuous intravenous infusion at a dose of 3 mg./kg. daily, targeting for a whole blood cyclosporine concentration of 250 to 400 mg./l. When the patient adequately tolerated oral intake 8 to 10 mg./kg. of cyclosporine micro-emulsion were introduced daily in 2 divided doses. In all groups the cyclosporine micro-emulsion dose was adjusted so that cyclosporine trough blood level remained in the target range of 250 to 400 mg./l. in month 1, and between 200 and 300 mg./l. in months 2 and 3, respectively. Intraoperatively 500 mg. methylprednisolone were given intravenously, followed by 1 mg./kg. prednisone daily given orally and tapered by 5 mg. every other day to 20, 15 and 10 mg. daily for months 1 to 3, respectively. Intraoperatively 3 mg./kg. aza* Incstar, Stillwater, Minnesota.
thioprine were given intravenously, followed by 1.5 mg./kg. given orally daily and subsequently adjusted to maintain a white blood count of greater than 4,000/mm.3. As soon as oral medication was tolerated, 1 gm. mycophenolate mofetil was started orally twice daily and adjusted to maintain a white blood count of greater than 4,000/mm.3. All patients not in the rapamycin study group who tolerated diltiazem and had no contraindications to its use were started on 120 mg. diltiazem daily postoperatively. Blood samples for cyclosporine determination were drawn before the dose (cyclosporine trough blood level), and 1, 2, 3 and 4 hours after the morning dose 2 to 4 days after the introduction of cyclosporine microemulsion (median post-transplantation day 4). Student’s t test was used to compare the means of continuous numeric values of cyclosporine trough blood level, blood levels after 1, 2 and 3 hours, and so forth in patients with or without acute rejection and cyclosporine nephrotoxicity. Stepwise logistic regression analysis was done to explore the associations of transplant source, panel-reactive antibody, HLA mismatch, type of immunosuppression, treatment with diltiazem, delayed graft function, cyclosporine trough blood level, cyclosporine blood level after 1 to 4 hours and cyclosporine micro-emulsion dose with the incidence of acute rejection and cyclosporine nephrotoxicity. The chi-square test was performed to compare the incidence of acute rejection and cyclosporine nephrotoxicity among groups. In all statistical analyses p ,0.05 was considered significant. Statistical calculations were done using computer software. RESULTS
Table 1 shows the characteristics of our study population. Outcome variables at 3 months indicate a 24% incidence of acute rejection in the 100 cadaver and 43 nonidentical live donor transplants, and a 19% incidence of cyclosporine nephrotoxicity in the overall population of 156 patients, including the 13 recipients of HLA identical live related donor transplants. Mean cyclosporine trough blood level plus or minus Standard error of mean did not differ in patients with or without acute rejection (293 6 21 versus 294 6 11 mg./l., p 5 0.95) but it was significantly higher in those with cyclosporine nephrotoxicity (343 6 18 versus 287 6 10 mg./l., p 5 0.01). Of the 34 patients with acute rejection 15 (44%) had a cyclosporine trough blood level within the therapeutic range of 250 to 400 mg./l., as did 16 of the 30 (53%) with cyclosporine nephrotoxicity. Table 2 shows mean cyclosporine blood level after 1 to 4 hours in patients with and without acute rejection and/or cyclosporine nephrotoxicity. Although the blood level after 2 hours was also significantly lower in patients with acute rejection and significantly higher in those with nephrotoxicity, when all individual time point cyclosporine concentrations were entered as independent variables in logistic regression analysis, only cyclosporine blood level after 3 hours was a significant predictor of acute rejection (p 5 0.03). Stepwise logistic regression analysis revealed that only the blood level after 3 hours (p 5 0.008) and delayed graft function (p 5 0.007) predicted acute rejection. There was no difference in patients with and without acute rejection in
TABLE 1. Patient characteristics Mean age 6 SD No. men (%) No. living related donor kidney (%): HLA identical NonHLA identical No. cadaveric donor kidney (%) Mos. followup Median HLA mismatches No. diabetes mellitus (%): No. greater than 30% panel-reactive antibody (%)
45 6 12 103 (66) 56 (36) 13 (8) 43 (28) 100 (64) Up to 3 3 25 (16) 9 (6)
39
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL? TABLE 2. Mean cyclosporine blood level values 1 to 4 hours after dose in patients with and without acute rejection and cyclosporine nephrotoxicity Mean Cyclosporine Level 6 SEM (mg./l.) Hrs. After Dose
Rejection (p value)
No Rejection (p value)
Nephrotoxicity (p value)
No Nephrotoxicity (p value)
1 2 3 4
882 6 113 1,293 6 114 (0.03) 1,156 6 90 (0.08) 1,015 6 82
1,080 6 70 1,573 6 61 (0.03) 1,421 6 50 (0.08) 1,152 6 43
993 6 61 1,456 6 56 (0.03) 1,318 6 45 (0.01) 1,095 6 41
1,129 6 149 1,750 6 131 (0.03) 1,581 6 109 (0.01) 1,275 6 79
regard to the trough blood level, cadaver versus nonidentical live donor transplant source, HLA mismatch, panel-reactive antibody, immunosuppression regimen, treatment with diltiazem and weight adjusted cyclosporine micro-emulsion dose. In stepwise logistic regression analysis for factors affecting cyclosporine nephrotoxicity only cyclosporine blood level after 3 hours (p 5 0.03) and weight adjusted cyclosporine micro-emulsion dose (p 5 0.009) entered the model. Trough blood level did not meet the 0.05 significance level for entry into the model whether diltiazem was or was not received, or according to patient gender, age, transplant source or immunosuppression regimen. Although weight adjusted cyclosporine micro-emulsion dose was significant in the stepwise regression model, it was not possible to identify a cutoff value above which there was a significant increase in the rate of nephrotoxicity because of significant mean overlap (10.1 6 0.4 versus 9.1 6 0.2) in cases with versus without nephrotoxicity. There was no statistically significant difference among the mycophenolate mofetil, rapamycin or azathioprine groups in regard to acute rejection and cyclosporine nephrotoxicity. There was also no difference in the incidence of acute rejection (26% versus 21%) or cyclosporine nephrotoxicity (19% versus 19%) in those receiving and not receiving diltiazem. Subsequently we further analyzed the association of cyclosporine blood level after 3 hours, acute rejection and cyclosporine nephrotoxicity. All 156 patients were divided according to cyclosporine blood level into 3 equal groups of 52 after 3 hours of less than 1,100, 1,1000 to less than 1,500 and greater than 1,500 mg./l. Figure 1 shows the acute rejection and cyclosporine nephrotoxicity rates in these groups. For comparison patients were also divided into 3 groups based on cyclosporine trough blood level and the therapeutic range used at our institution of less than 250, 250 to less than 400
and greater than 400 mg./l. Figure 2 shows the acute rejection and cyclosporine nephrotoxicity rates in the trough level groups. Of the 100 cadaveric transplants 15 had delayed graft function, and 8 (53%) had acute rejection compared with 20% acute rejection after cadaveric transplantation without delayed graft function (chi-square test p 5 0.003). Due to the small number of patients the effect of cyclosporine blood level after 3 hours on acute rejection in patients with delayed graft function was not analyzed. DISCUSSION
Given the wide variation in cyclosporine absorption and metabolism, the consequences of inadequate immunossuppression and toxicity associated with high drug exposure, at almost all transplant centers cyclosporine levels are routinely monitored. Monitoring by cyclosporine trough blood level has become the standard. However, studies from different centers have shown a poor correlation of cyclosporine trough blood level, and better correlation of area under the curve of blood cyclosporine concentration versus time with acute rejection and graft survival in kidney transplant recipients.1, 3, 4, 15, 16 Although the interactions between graft and host are complex and not well understood, and many immunological and nonimmunological factors have a role in the development of acute rejection and graft survival, at least 3 independent studies have shown that early cyclosporine exposure in week 1 after transplantation, as measured by area under the curve of blood cyclosporine concentration versus time and/or maximum cyclosporine blood concentration, has an important effect on acute rejection and/or graft survival. Lindholm and Kahan prospectively monitored original formula cyclosporine
FIG. 1. Incidence of acute rejection (AR) and cyclosporine nephrotoxicity (CyANT) in patients with different ranges of cyclosporine blood level values after 3 hours (C3). HLA identical recipients were excluded from acute rejection analysis.
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IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
FIG. 2. Incidence of acute rejection (AR) and cyclosporine nephrotoxicity (CyANT) in patients with different ranges of cyclosporine trough blood level (C0) values indicates no statistically significant difference among groups (p .0.05). HLA identical recipients were excluded from acute rejection analysis.
dosing by serial area under the curve of blood cyclosporine concentration versus time in 160 kidney transplant recipients.3 They noted that an average cyclosporine blood concentration of less than 400 ng./ml. on the initial posttransplantation pharmacokinetic study only (postoperative day 7) was associated with poorer 1-year graft survival and a higher acute rejection rate. In an extension of that study Senel et al reported that an average cyclosporine blood concentration of greater than 550 ng./ml. on posttransplantation day 7 was associated with higher graft survival at 1, 2, 3 and 6 months, and 1 and 6 years as well as with less severe episodes of acute rejection in 290 kidney transplant recipients.4 We recently reported a retrospective study of 156 initial kidney transplant recipients receiving cyclosporine microemulsion based triple immunosuppression.17 An area under the curve of blood cyclosporine concentration versus time (hourly samples, before to 4 hours after dose) range of 4,400 to 5,500 mg./l. per hour on days 2 to 4 was associated with the lowest rate of acute rejection (7%) and nephrotoxicity (6%) 3 months after transplantation. In addition, Grant et al showed that the 6-hour area under the curve value and maximum cyclosporine blood concentration on day 5 were strongly associated with freedom from acute rejection in liver transplant recipients treated with cyclosporine microemulsion.18 However, the inconvenience and cost of multiple blood samples every 12 to 24 hours have inhibited more widespread monitoring of area under the curve values. With cyclosporine micro-emulsion, and its superior and more consistent pharmacokinetic characteristics5, 6 the potential exists for better therapeutic monitoring of cyclosporine. For cyclosporine monitoring to be acceptable and incorporated into routine practice the frequency of area under the curve assays must be low or a single post-dose value for cyclosporine blood concentration must be sufficient. The results of our study suggest that the cyclosporine blood level after 3 hours may be a better monitoring parameter than the trough blood level for cyclosporine micro-emulsion. We also defined a 1,100 to 1,500 mg./l. range for the blood level after 3 hours that was associated with a significant decrease in acute rejection without increased cyclosporine nephrotoxicity. Our study is not the first to evaluate a single post-dose blood level for monitoring cyclosporine. Cantarovich et al showed that de novo heart transplant recipients monitored by cyclosporine blood level after 6 hours required significantly less cyclosporine (original formula) 1, 3, 6 and 9 months after transplantation than those monitored by cyclosporine trough blood level.11 In the 2 groups at 12 months the
cyclosporine dose difference was not significant, while at all time points serum creatinine was not significantly different. However, Cantarovich et al concluded that monitoring after 6 hours may prevent cyclosporine nephrotoxicity based on the need for lower doses. They also recently reported their experience with monitoring after 2 hours of cyclosporine microemulsion in stable heart and liver recipients.12 In stable heart transplant recipients targeting a blood level range after 2 hours of 200 to 400 ng./ml. resulted in a significant decrease in cyclosporine micro-emulsion dose and lower serum creatinine without causing acute rejection compared with cyclosporine trough blood level monitoring. In stable liver transplant patients monitoring cyclosporine microemulsion dose by cyclosporine blood level after 2 hours, targeting a range of 300 to 600 ng./ml., decreased the cyclosporine micro-emulsion dose significantly compared with cyclosporine trough blood level. However, serum creatinine was comparable in the 2 groups.13 In a Canadian liver transplant study in which new liver transplant recipients were randomized to receive cyclosporine (original formula) or cyclosporine micro-emulsion a maximum cyclosporine blood concentration of greater than 850 ng./ml. at day 10 was associated with significantly fewer episodes of acute rejection.14 The blood level after 2 hours showed excellent correlation with maximum cyclosporine blood concentration and it was considered a suitable tool for monitoring cyclosporine dosing. No data regarding cyclosporine nephrotoxicity were reported. However, in this study the cyclosporine dose was monitored by cyclosporine trough blood level. In our study cyclosporine blood level after 3 hours appeared to be the best estimate of efficacy and toxicity compared with all single time point cyclosporine concentrations tested. Although cyclosporine blood level after 2 hours was significantly different in patients with and without acute rejection and/or cyclosporine nephrotoxicity, only cyclosporine blood level after 3 hours was an independent predictor of acute rejection and nephrotoxicity. In our study the comparison of cyclosporine blood levels after 2 and 3 hours favored the 3-hour level, which may be attributed to several factors. Cyclosporine blood level after 3 hours was not evaluated or mentioned in other reports. We determined cyclosporine blood level after 3 hours at an earlier postoperative time. Cyclosporine micro-emulsion absorption may be delayed but drug exposure may be more critical to prevent rejection during this period. The pharmacokinetic-pharmacodynamic characteristics of cyclosporine micro-emulsion may be different in different organ transplants. Nevertheless, our study is consistent with those of others since all address the need for
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
a more reliable and predictable measure of therapeutic monitoring. 8. CONCLUSIONS
Cyclosporine trough blood level correlates poorly with acute rejection and cyclosporine nephrotoxicity. Cyclosporine blood level 3 hours after renal transplantation is closely associated with acute rejection and cyclosporine nephrotoxicity. To our knowledge this is the first study to show a correlation of a single post-dose cyclosporine concentration with acute rejection and nephrotoxicity in kidney transplant recipients. Cyclosporine blood level after 3 hours may be a better, more convenient and acceptable method of monitoring cyclosporine micro-emulsion dosing than cyclosporine trough blood level. The safety and efficacy of dosing cyclosporine micro-emulsion according to the blood level after 3 hours in kidney transplant recipients require a formal prospective randomized study. REFERENCES
1. Nankivell, B. J., Hibbins, M. and Chapman, J. R.: Diagnostic utility of whole blood cyclosporine measurements in renal transplantation using triple therapy. Transplantation, 58: 989, 1994. 2. Oellerich, M., Armstrong, V. W., Kahan, B. et al: Lake Louise consensus conference on cyclosporine monitoring in organ transplantation: report of the consensus panel. Ther Drug Monit, 17: 642, 1995. 3. Lindholm, A. and Kahan, B. D.: Influence of cyclosporine pharmacokinetics, trough concentrations, and AUC monitoring on outcome after kidney transplantation. Clin Pharmacol Ther, 54: 205, 1993. 4. Senel, M. F., Van Buren, C. T., Welsh, M. et al: Impact of early cyclosporin average blood concentration on early kidney transplant failure. Transplant Int, 11: 46, 1998. 5. Kovarik, J. M., Mueller, E. A. and Niese, D.: Clinical development of a cyclosporine microemulsion in transplantation. Ther Drug Monit, 18: 429, 1996. 6. Holt, D. W., Mueller, E A., Kovarik, J. M. et al: The pharmacokinetics of Sandimmun Neoral: a new oral formulation of cyclosporine. Transplant Proc, 26: 2935, 1994. 7. Barone, G., Chang, C. T., Choc, M. G., Jr. et al: The pharmacokinetics of a microemulsion formulation of cyclosporine in
9.
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12. 13.
14. 15. 16.
17.
18.
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primary renal allograft recipients. The Neoral Study Group. Transplantation, 61: 875, 1996. Niese, D.: A double-blind randomized study of Sandimmun Neoral versus Sandimmun in new renal transplant recipients: results after 12 months. The International Sandimmun Neoral Study Group. Transplant Proc, 27: 1849, 1995. Lodge, J. P. and Pollard, S. G.: Neoral vs Sandimmun: interim results of a randomized trial of efficacy and safety in preventing acute rejection in new renal transplant recipients. Transplant Proc, 29: 272, 1997. Barone, G., Bunke, C. M., Choc, M. G. et al: The safety and tolerability of cyclosporine emulsion versus cyclosporine in a randomized, double-blind comparison in primary renal allograft recipients. The Neoral Study Group. Transplantation, 61: 968, 1996. Cantarovich, M., Latter, D. and Fitchett, D.: Comparison of cyclosporine monitoring with trough levels to levels obtained 6 hours after the morning dose in heart transplant patients: a prospective randomized study. Transplant Proc, 29: 602, 1997. Cantarovich, M., Besner, J. G., Barkun, J. S. et al: Two-hour cyclosporine level determination is the appropriate tool to monitor Neoral therapy. Clin Transplant, 12: 243, 1998. Cantarovich, M., Barkun, J. S., Tchervenkov, J. I. et al: Comparison of Neoral dose monitoring with cyclosporine trough levels versus 2-hour postdose levels in stable liver transplant patients. Transplantation, 66: 1621, 1998. Canadian Liver Transplant Study Group. Importance of cyclosporine pharmacokinetics to clinical outcomes after liver transplantation. Transplant Proc, 30: 1826, 1998. Meyer, M. M., Munar, M., Udeaja, J. et al: Efficacy of area under the curve cyclosporine monitoring in renal transplantation. J Am Soc Nephrol, 4: 1306, 1993. Kasiske, B. L., Heim-Duthoy, K., Rao, K. V. et al: The relationship between cyclosporine pharmacokinetic parameters and subsequent acute rejection in renal transplant recipients. Transplantation, 46: 716, 1998. Mahalati, K., Belitsky, P., Sketris, I. et al: Neoral monitoring by simplified sparse sampling area under the concentration-time curve: its relationship to acute rejection and cyclosporine nephrotoxicity early after kidney transplantation. Transplantation, 68: 55, 1999. Grant, D., Kneteman, N., Tchervenkov, J. et al: Peak cyclosporine levels (Cmax) correlate with freedom from liver graft rejection: results of a prospective randomized comparison of Neoral and sandimmune for liver transplantation (NOF-8). Transplantation, 67: 1133, 1999.
Vol. 163, 37– 41, January 2000 Printed in U.S.A.
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL IN EARLY POST-RENAL TRANSPLANTATION PERIOD? KAMRAN MAHALATI, JOSEPH LAWEN, BRYCE KIBERD
AND
PHILIP BELITSKY
From the Kidney Transplant Program, and Departments of Urology and Medicine, Dalhousie University, Queen Elizabeth II Health Sciences Centre, Halifax, Nova Scotia, Canada
ABSTRACT
Purpose: Cyclosporine dose is traditionally based on trough blood levels. Cyclosporine trough blood level correlates poorly with acute rejection and cyclosporine nephrotoxicity after renal transplantation. We determined whether cyclosporine blood level at any other time point is superior to cyclosporine trough blood level as a predictor of acute rejection and cyclosporine nephrotoxicity. Materials and Methods: Cyclosporine blood level was measured before (trough), and 1, 2, 3 and 4 hours after the dose in 156 initial renal transplant cases 2 to 4 days after the initiation of cyclosporine micro-emulsion formula administration. The cylosporine micro-emulsion dose was based on cyclosporine trough blood level targeting 250 to 400 mg./l. Results: Regression analysis revealed that only delayed graft function (p 5 0.007) and cyclosporine blood level after 3 hours (p 5 0.008) predicted acute rejection. Mean cyclosporine trough blood level plus or minus standard error was not significantly different in patients with and without acute rejection (293 6 21 versus 294 6 11 mg./l.). Mean cyclosporine blood level after 3 hours was significantly lower in patients with acute rejection (1,156 6 90 versus 1,421 6 50, p 5 0.008). Cases were divided into tertiles at levels after 3 hours (1,100 and 1,500 mg./l.). The group in which the level after 3 hours was less than 1,100 mg./l. had the highest acute rejection rate (22 of 50 patients, 44%) and a cyclosporine nephrotoxicity rate of 13% (7 of 52 patients). The group in which the level after 3 hours was 1,100 to 1,500 mg./l. had the lowest acute rejection rate (5 of 46 patients, 11%) without increased cyclosporine nephrotoxicity (7 of 52 patients, 13%). A level after 3 hours of greater than 1,500 mg./l. was associated with a rejection rate of 15% (7 of 47 patients) but significantly higher cyclosporine nephrotoxicity (16 of 52 patients, 30%). Conclusions: Cyclosporine blood level after 3 hours in the early post-transplantation period is associated with acute rejection and cyclosporine nephrotoxicity. A cyclosporine blood level range after 3 hours of 1,100 to 1,500 mg./l. is associated with an optimal outcome. Our data suggest that cyclosporine blood level after 3 hours may represent a better method of monitoring cyclosporine micro-emulsion dose than cyclosporine trough blood level. This hypothesis must be further studied in randomized trials. KEY WORDS: kidney, cyclosporine, drug monitoring, kidney transplantation, rejection
Cyclosporine is the foundation of current immunosuppression protocols at many kidney transplant centers. Therapeutic monitoring of the drug is essential because cyclosporine has a narrow therapeutic window with serious potential side effects. Cyclosporine trough blood level, that is immediately before the next dose, has been widely used for monitoring the cyclosporine dose. Although the correlation of cyclosporine trough blood level with post-transplantation adverse clinical events, such as acute rejection and acute cyclosporine nephrotoxicity, is poor, cyclosporine trough blood level is still widely used to monitor cyclosporine treatment. Significant groups of patients have acute rejection or cyclosporine nephrotoxicity despite the maintenance of cyclosporine levels within the therapeutic range, which tends to be variable and center specific.1, 2 The area under the curve of blood cyclosporine concentration versus time is a better measurement of systemic drug exposure than cyclosporine trough blood level. The area value within week 1 after transplantation has been shown to correlate with 1-year acute rejection and graft survival after kidney transplantation.3, 4 However, therapeutic monitoring of cyclosporine based on pharmacokinetic studies and the area value has not gained popularity, largely because of the
inconvenience of multiple blood sampling during 12 hours, and the costs associated with sampling and analysis. A new galenic formulation of cyclosporine, cyclosporine micro-emulsion, is designed to overcome the absorption problems of the cyclosporine standard formulation. Cyclosporine micro-emulsion has more extensive, predictable and consistent oral absorption, less intra-subject variability, increased dose linearity with the value of the area under the curve of blood cyclosporine concentration versus time, and better but not perfect correlation of cyclosporine trough blood level and area value than the standard formulation. The hope was that cyclosporine micro-emulsion would provide more predictable drug exposure that would be reliably reflected by cyclosporine trough blood level, and result in better immunosuppression with fewer side effects.5–7 Subsequent randomized clinical trials in new kidney transplant patients showed a comparable toleration and side effect profile of the 2 cyclosporine formulations, and a lower but still significant rate of acute rejection (35% to 45%)8 –10 with cyclosporine microemulsion. The more predictable pharmacokinetic characteristics of cyclosporine micro-emulsion, and the need for a simpler and more effective way to monitor cyclosporine have led a few groups to use single post-dose cyclosporine levels for this
Accepted for publication August 13, 1999. 37
38
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
purpose. The 2 and 6-hour post-dose cyclosporine blood levels have been shown to be a useful method of monitoring cyclosporine in new and stable liver and heart transplant recipients.11–14 We examined the correlation of cyclosporine blood concentrations in the initial 4 hours after the dose measured at week 1 after transplantation with acute rejection and cyclosporine nephrotoxicity during the initial 3 months after renal transplantation. MATERIALS AND METHODS
The study population comprised 156 consecutive initial kidney transplant recipients who underwent transplantation between August 1995 and January 1998 at our institution. All patients received cyclosporine micro-emulsion based immunosuppression and none received antibody induction. Followup for the purpose of this analysis was 3 months after transplantation. Of the 156 patients 100 (64%) received cadaver, 43 (28%) nonidentical live and 13 (8%) HLA identical live donor kidneys. The latter 13 cases are included only in the analysis of cyclosporine nephrotoxicity and not acute rejection. Inpatient and outpatient records were reviewed retrospectively for episodes of acute rejection and cyclosporine nephrotoxicity within the initial 3 months after transplantation. Cyclosporine micro-emulsion dose, cyclosporine trough blood level and serum creatinine on days 1 to 14, weeks 3 to 7, and months 2 and 3 after transplantation were noted, as were patient demographics, cadaveric versus living related transplant source, panel-reactive antibody, immunosuppression regimen, HLA mismatch and delayed graft function. The diagnosis of acute rejection was confirmed by percutaneous core needle biopsy with severity classified according to the Banff criteria. Cyclosporine nephrotoxicity was defined as a greater than 30% increase in serum creatinine that was not attributable to any other identifiable cause and improved with a decrease in the cyclosporine micro-emulsion dose. Biopsies performed for renal dysfunction were free of acute rejection changes and exhibited abnormalities attributable to cyclosporine toxicity. Delayed graft function was defined as the lack of a greater than 10% spontaneous decrease in serum creatinine by day 3 postoperatively regardless of the need for dialysis. All cyclosporine blood values refer to whole blood concentrations and were determined using the monoclonal, parent compound specific, whole blood Cyclo-Trac RIA* test kit. The 13 recipients of HLA identical living related transplants were treated with prednisone and cyclosporine microemulsion only. The other 143 patients were divided into the azathioprine group—19 (13%) who received prednisone, cyclosporine micro-emulsion and azathioprine; the mycophenolate mofetil group— 61 (43%) who received prednisone, cyclosporine micro-emulsion and mycophenolate mofetil, and the rapamycin group— 63 (44%) who received prednisone, cyclosporine micro-emulsion and 5 or 2 mg. rapamycin or placebo in a 2:2:1 ratio as part of a randomized double-blind study. Cyclosporine was administered for the initial 1 to 3 days after transplantation by continuous intravenous infusion at a dose of 3 mg./kg. daily, targeting for a whole blood cyclosporine concentration of 250 to 400 mg./l. When the patient adequately tolerated oral intake 8 to 10 mg./kg. of cyclosporine micro-emulsion were introduced daily in 2 divided doses. In all groups the cyclosporine micro-emulsion dose was adjusted so that cyclosporine trough blood level remained in the target range of 250 to 400 mg./l. in month 1, and between 200 and 300 mg./l. in months 2 and 3, respectively. Intraoperatively 500 mg. methylprednisolone were given intravenously, followed by 1 mg./kg. prednisone daily given orally and tapered by 5 mg. every other day to 20, 15 and 10 mg. daily for months 1 to 3, respectively. Intraoperatively 3 mg./kg. aza* Incstar, Stillwater, Minnesota.
thioprine were given intravenously, followed by 1.5 mg./kg. given orally daily and subsequently adjusted to maintain a white blood count of greater than 4,000/mm.3. As soon as oral medication was tolerated, 1 gm. mycophenolate mofetil was started orally twice daily and adjusted to maintain a white blood count of greater than 4,000/mm.3. All patients not in the rapamycin study group who tolerated diltiazem and had no contraindications to its use were started on 120 mg. diltiazem daily postoperatively. Blood samples for cyclosporine determination were drawn before the dose (cyclosporine trough blood level), and 1, 2, 3 and 4 hours after the morning dose 2 to 4 days after the introduction of cyclosporine microemulsion (median post-transplantation day 4). Student’s t test was used to compare the means of continuous numeric values of cyclosporine trough blood level, blood levels after 1, 2 and 3 hours, and so forth in patients with or without acute rejection and cyclosporine nephrotoxicity. Stepwise logistic regression analysis was done to explore the associations of transplant source, panel-reactive antibody, HLA mismatch, type of immunosuppression, treatment with diltiazem, delayed graft function, cyclosporine trough blood level, cyclosporine blood level after 1 to 4 hours and cyclosporine micro-emulsion dose with the incidence of acute rejection and cyclosporine nephrotoxicity. The chi-square test was performed to compare the incidence of acute rejection and cyclosporine nephrotoxicity among groups. In all statistical analyses p ,0.05 was considered significant. Statistical calculations were done using computer software. RESULTS
Table 1 shows the characteristics of our study population. Outcome variables at 3 months indicate a 24% incidence of acute rejection in the 100 cadaver and 43 nonidentical live donor transplants, and a 19% incidence of cyclosporine nephrotoxicity in the overall population of 156 patients, including the 13 recipients of HLA identical live related donor transplants. Mean cyclosporine trough blood level plus or minus Standard error of mean did not differ in patients with or without acute rejection (293 6 21 versus 294 6 11 mg./l., p 5 0.95) but it was significantly higher in those with cyclosporine nephrotoxicity (343 6 18 versus 287 6 10 mg./l., p 5 0.01). Of the 34 patients with acute rejection 15 (44%) had a cyclosporine trough blood level within the therapeutic range of 250 to 400 mg./l., as did 16 of the 30 (53%) with cyclosporine nephrotoxicity. Table 2 shows mean cyclosporine blood level after 1 to 4 hours in patients with and without acute rejection and/or cyclosporine nephrotoxicity. Although the blood level after 2 hours was also significantly lower in patients with acute rejection and significantly higher in those with nephrotoxicity, when all individual time point cyclosporine concentrations were entered as independent variables in logistic regression analysis, only cyclosporine blood level after 3 hours was a significant predictor of acute rejection (p 5 0.03). Stepwise logistic regression analysis revealed that only the blood level after 3 hours (p 5 0.008) and delayed graft function (p 5 0.007) predicted acute rejection. There was no difference in patients with and without acute rejection in
TABLE 1. Patient characteristics Mean age 6 SD No. men (%) No. living related donor kidney (%): HLA identical NonHLA identical No. cadaveric donor kidney (%) Mos. followup Median HLA mismatches No. diabetes mellitus (%): No. greater than 30% panel-reactive antibody (%)
45 6 12 103 (66) 56 (36) 13 (8) 43 (28) 100 (64) Up to 3 3 25 (16) 9 (6)
39
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL? TABLE 2. Mean cyclosporine blood level values 1 to 4 hours after dose in patients with and without acute rejection and cyclosporine nephrotoxicity Mean Cyclosporine Level 6 SEM (mg./l.) Hrs. After Dose
Rejection (p value)
No Rejection (p value)
Nephrotoxicity (p value)
No Nephrotoxicity (p value)
1 2 3 4
882 6 113 1,293 6 114 (0.03) 1,156 6 90 (0.08) 1,015 6 82
1,080 6 70 1,573 6 61 (0.03) 1,421 6 50 (0.08) 1,152 6 43
993 6 61 1,456 6 56 (0.03) 1,318 6 45 (0.01) 1,095 6 41
1,129 6 149 1,750 6 131 (0.03) 1,581 6 109 (0.01) 1,275 6 79
regard to the trough blood level, cadaver versus nonidentical live donor transplant source, HLA mismatch, panel-reactive antibody, immunosuppression regimen, treatment with diltiazem and weight adjusted cyclosporine micro-emulsion dose. In stepwise logistic regression analysis for factors affecting cyclosporine nephrotoxicity only cyclosporine blood level after 3 hours (p 5 0.03) and weight adjusted cyclosporine micro-emulsion dose (p 5 0.009) entered the model. Trough blood level did not meet the 0.05 significance level for entry into the model whether diltiazem was or was not received, or according to patient gender, age, transplant source or immunosuppression regimen. Although weight adjusted cyclosporine micro-emulsion dose was significant in the stepwise regression model, it was not possible to identify a cutoff value above which there was a significant increase in the rate of nephrotoxicity because of significant mean overlap (10.1 6 0.4 versus 9.1 6 0.2) in cases with versus without nephrotoxicity. There was no statistically significant difference among the mycophenolate mofetil, rapamycin or azathioprine groups in regard to acute rejection and cyclosporine nephrotoxicity. There was also no difference in the incidence of acute rejection (26% versus 21%) or cyclosporine nephrotoxicity (19% versus 19%) in those receiving and not receiving diltiazem. Subsequently we further analyzed the association of cyclosporine blood level after 3 hours, acute rejection and cyclosporine nephrotoxicity. All 156 patients were divided according to cyclosporine blood level into 3 equal groups of 52 after 3 hours of less than 1,100, 1,1000 to less than 1,500 and greater than 1,500 mg./l. Figure 1 shows the acute rejection and cyclosporine nephrotoxicity rates in these groups. For comparison patients were also divided into 3 groups based on cyclosporine trough blood level and the therapeutic range used at our institution of less than 250, 250 to less than 400
and greater than 400 mg./l. Figure 2 shows the acute rejection and cyclosporine nephrotoxicity rates in the trough level groups. Of the 100 cadaveric transplants 15 had delayed graft function, and 8 (53%) had acute rejection compared with 20% acute rejection after cadaveric transplantation without delayed graft function (chi-square test p 5 0.003). Due to the small number of patients the effect of cyclosporine blood level after 3 hours on acute rejection in patients with delayed graft function was not analyzed. DISCUSSION
Given the wide variation in cyclosporine absorption and metabolism, the consequences of inadequate immunossuppression and toxicity associated with high drug exposure, at almost all transplant centers cyclosporine levels are routinely monitored. Monitoring by cyclosporine trough blood level has become the standard. However, studies from different centers have shown a poor correlation of cyclosporine trough blood level, and better correlation of area under the curve of blood cyclosporine concentration versus time with acute rejection and graft survival in kidney transplant recipients.1, 3, 4, 15, 16 Although the interactions between graft and host are complex and not well understood, and many immunological and nonimmunological factors have a role in the development of acute rejection and graft survival, at least 3 independent studies have shown that early cyclosporine exposure in week 1 after transplantation, as measured by area under the curve of blood cyclosporine concentration versus time and/or maximum cyclosporine blood concentration, has an important effect on acute rejection and/or graft survival. Lindholm and Kahan prospectively monitored original formula cyclosporine
FIG. 1. Incidence of acute rejection (AR) and cyclosporine nephrotoxicity (CyANT) in patients with different ranges of cyclosporine blood level values after 3 hours (C3). HLA identical recipients were excluded from acute rejection analysis.
40
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
FIG. 2. Incidence of acute rejection (AR) and cyclosporine nephrotoxicity (CyANT) in patients with different ranges of cyclosporine trough blood level (C0) values indicates no statistically significant difference among groups (p .0.05). HLA identical recipients were excluded from acute rejection analysis.
dosing by serial area under the curve of blood cyclosporine concentration versus time in 160 kidney transplant recipients.3 They noted that an average cyclosporine blood concentration of less than 400 ng./ml. on the initial posttransplantation pharmacokinetic study only (postoperative day 7) was associated with poorer 1-year graft survival and a higher acute rejection rate. In an extension of that study Senel et al reported that an average cyclosporine blood concentration of greater than 550 ng./ml. on posttransplantation day 7 was associated with higher graft survival at 1, 2, 3 and 6 months, and 1 and 6 years as well as with less severe episodes of acute rejection in 290 kidney transplant recipients.4 We recently reported a retrospective study of 156 initial kidney transplant recipients receiving cyclosporine microemulsion based triple immunosuppression.17 An area under the curve of blood cyclosporine concentration versus time (hourly samples, before to 4 hours after dose) range of 4,400 to 5,500 mg./l. per hour on days 2 to 4 was associated with the lowest rate of acute rejection (7%) and nephrotoxicity (6%) 3 months after transplantation. In addition, Grant et al showed that the 6-hour area under the curve value and maximum cyclosporine blood concentration on day 5 were strongly associated with freedom from acute rejection in liver transplant recipients treated with cyclosporine microemulsion.18 However, the inconvenience and cost of multiple blood samples every 12 to 24 hours have inhibited more widespread monitoring of area under the curve values. With cyclosporine micro-emulsion, and its superior and more consistent pharmacokinetic characteristics5, 6 the potential exists for better therapeutic monitoring of cyclosporine. For cyclosporine monitoring to be acceptable and incorporated into routine practice the frequency of area under the curve assays must be low or a single post-dose value for cyclosporine blood concentration must be sufficient. The results of our study suggest that the cyclosporine blood level after 3 hours may be a better monitoring parameter than the trough blood level for cyclosporine micro-emulsion. We also defined a 1,100 to 1,500 mg./l. range for the blood level after 3 hours that was associated with a significant decrease in acute rejection without increased cyclosporine nephrotoxicity. Our study is not the first to evaluate a single post-dose blood level for monitoring cyclosporine. Cantarovich et al showed that de novo heart transplant recipients monitored by cyclosporine blood level after 6 hours required significantly less cyclosporine (original formula) 1, 3, 6 and 9 months after transplantation than those monitored by cyclosporine trough blood level.11 In the 2 groups at 12 months the
cyclosporine dose difference was not significant, while at all time points serum creatinine was not significantly different. However, Cantarovich et al concluded that monitoring after 6 hours may prevent cyclosporine nephrotoxicity based on the need for lower doses. They also recently reported their experience with monitoring after 2 hours of cyclosporine microemulsion in stable heart and liver recipients.12 In stable heart transplant recipients targeting a blood level range after 2 hours of 200 to 400 ng./ml. resulted in a significant decrease in cyclosporine micro-emulsion dose and lower serum creatinine without causing acute rejection compared with cyclosporine trough blood level monitoring. In stable liver transplant patients monitoring cyclosporine microemulsion dose by cyclosporine blood level after 2 hours, targeting a range of 300 to 600 ng./ml., decreased the cyclosporine micro-emulsion dose significantly compared with cyclosporine trough blood level. However, serum creatinine was comparable in the 2 groups.13 In a Canadian liver transplant study in which new liver transplant recipients were randomized to receive cyclosporine (original formula) or cyclosporine micro-emulsion a maximum cyclosporine blood concentration of greater than 850 ng./ml. at day 10 was associated with significantly fewer episodes of acute rejection.14 The blood level after 2 hours showed excellent correlation with maximum cyclosporine blood concentration and it was considered a suitable tool for monitoring cyclosporine dosing. No data regarding cyclosporine nephrotoxicity were reported. However, in this study the cyclosporine dose was monitored by cyclosporine trough blood level. In our study cyclosporine blood level after 3 hours appeared to be the best estimate of efficacy and toxicity compared with all single time point cyclosporine concentrations tested. Although cyclosporine blood level after 2 hours was significantly different in patients with and without acute rejection and/or cyclosporine nephrotoxicity, only cyclosporine blood level after 3 hours was an independent predictor of acute rejection and nephrotoxicity. In our study the comparison of cyclosporine blood levels after 2 and 3 hours favored the 3-hour level, which may be attributed to several factors. Cyclosporine blood level after 3 hours was not evaluated or mentioned in other reports. We determined cyclosporine blood level after 3 hours at an earlier postoperative time. Cyclosporine micro-emulsion absorption may be delayed but drug exposure may be more critical to prevent rejection during this period. The pharmacokinetic-pharmacodynamic characteristics of cyclosporine micro-emulsion may be different in different organ transplants. Nevertheless, our study is consistent with those of others since all address the need for
IS 3-HOUR CYCLOSPORINE BLOOD LEVEL SUPERIOR TO TROUGH LEVEL?
a more reliable and predictable measure of therapeutic monitoring. 8. CONCLUSIONS
Cyclosporine trough blood level correlates poorly with acute rejection and cyclosporine nephrotoxicity. Cyclosporine blood level 3 hours after renal transplantation is closely associated with acute rejection and cyclosporine nephrotoxicity. To our knowledge this is the first study to show a correlation of a single post-dose cyclosporine concentration with acute rejection and nephrotoxicity in kidney transplant recipients. Cyclosporine blood level after 3 hours may be a better, more convenient and acceptable method of monitoring cyclosporine micro-emulsion dosing than cyclosporine trough blood level. The safety and efficacy of dosing cyclosporine micro-emulsion according to the blood level after 3 hours in kidney transplant recipients require a formal prospective randomized study. REFERENCES
1. Nankivell, B. J., Hibbins, M. and Chapman, J. R.: Diagnostic utility of whole blood cyclosporine measurements in renal transplantation using triple therapy. Transplantation, 58: 989, 1994. 2. Oellerich, M., Armstrong, V. W., Kahan, B. et al: Lake Louise consensus conference on cyclosporine monitoring in organ transplantation: report of the consensus panel. Ther Drug Monit, 17: 642, 1995. 3. Lindholm, A. and Kahan, B. D.: Influence of cyclosporine pharmacokinetics, trough concentrations, and AUC monitoring on outcome after kidney transplantation. Clin Pharmacol Ther, 54: 205, 1993. 4. Senel, M. F., Van Buren, C. T., Welsh, M. et al: Impact of early cyclosporin average blood concentration on early kidney transplant failure. Transplant Int, 11: 46, 1998. 5. Kovarik, J. M., Mueller, E. A. and Niese, D.: Clinical development of a cyclosporine microemulsion in transplantation. Ther Drug Monit, 18: 429, 1996. 6. Holt, D. W., Mueller, E A., Kovarik, J. M. et al: The pharmacokinetics of Sandimmun Neoral: a new oral formulation of cyclosporine. Transplant Proc, 26: 2935, 1994. 7. Barone, G., Chang, C. T., Choc, M. G., Jr. et al: The pharmacokinetics of a microemulsion formulation of cyclosporine in
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primary renal allograft recipients. The Neoral Study Group. Transplantation, 61: 875, 1996. Niese, D.: A double-blind randomized study of Sandimmun Neoral versus Sandimmun in new renal transplant recipients: results after 12 months. The International Sandimmun Neoral Study Group. Transplant Proc, 27: 1849, 1995. Lodge, J. P. and Pollard, S. G.: Neoral vs Sandimmun: interim results of a randomized trial of efficacy and safety in preventing acute rejection in new renal transplant recipients. Transplant Proc, 29: 272, 1997. Barone, G., Bunke, C. M., Choc, M. G. et al: The safety and tolerability of cyclosporine emulsion versus cyclosporine in a randomized, double-blind comparison in primary renal allograft recipients. The Neoral Study Group. Transplantation, 61: 968, 1996. Cantarovich, M., Latter, D. and Fitchett, D.: Comparison of cyclosporine monitoring with trough levels to levels obtained 6 hours after the morning dose in heart transplant patients: a prospective randomized study. Transplant Proc, 29: 602, 1997. Cantarovich, M., Besner, J. G., Barkun, J. S. et al: Two-hour cyclosporine level determination is the appropriate tool to monitor Neoral therapy. Clin Transplant, 12: 243, 1998. Cantarovich, M., Barkun, J. S., Tchervenkov, J. I. et al: Comparison of Neoral dose monitoring with cyclosporine trough levels versus 2-hour postdose levels in stable liver transplant patients. Transplantation, 66: 1621, 1998. Canadian Liver Transplant Study Group. Importance of cyclosporine pharmacokinetics to clinical outcomes after liver transplantation. Transplant Proc, 30: 1826, 1998. Meyer, M. M., Munar, M., Udeaja, J. et al: Efficacy of area under the curve cyclosporine monitoring in renal transplantation. J Am Soc Nephrol, 4: 1306, 1993. Kasiske, B. L., Heim-Duthoy, K., Rao, K. V. et al: The relationship between cyclosporine pharmacokinetic parameters and subsequent acute rejection in renal transplant recipients. Transplantation, 46: 716, 1998. Mahalati, K., Belitsky, P., Sketris, I. et al: Neoral monitoring by simplified sparse sampling area under the concentration-time curve: its relationship to acute rejection and cyclosporine nephrotoxicity early after kidney transplantation. Transplantation, 68: 55, 1999. Grant, D., Kneteman, N., Tchervenkov, J. et al: Peak cyclosporine levels (Cmax) correlate with freedom from liver graft rejection: results of a prospective randomized comparison of Neoral and sandimmune for liver transplantation (NOF-8). Transplantation, 67: 1133, 1999.