Adjusting cyclosporine (CsA) dose based on blood concentration at 2 hours after dose (C2) has been shown in prospective clinical trials to reduce the risk of rejection compared with conventional trough monitoring. In addition, it provides equivalent efficacy to tacrolimus in liver transplant patients, with a favorable safety profile. Target C2 should be defined on an individual basis depending on adjunctive therapy and the level of exposure required. It appears less critical to achieve target C2 in the first few days after liver transplantation than was previously believed. Achieving target C2 exposure in the initial period after transplant requires that changes in the proportion of cyclosporine absorbed from the gut be taken into account to avoid risk of overexposure. In addition, if a starting dose of 10–15 mg/day is used, it is advisable to delay increasing the dose until a trend in C2 level indicates this to be necessary. Immediate dose reduction is required if C2 exceeds target range. In patients with low C2 values, cyclosporine concentration at a later time point should be measured to establish whether the patient is a poor absorber or a delayed absorber of C2, and dose adjustments should be undertaken accordingly. In conclusion, this more flexible approach to C2 monitoring allows the dose of cyclosporine to be individualized effectively for each patient, which results in significant efficacy benefits while minimizing the risk of toxicity. (Liver Transpl 2004;10:577–583.)
Cyclosporine (CsA) dose adjustments based on blood concentration at 2 hours after dose (C2) have been shown to allow more sensitive individualization of drug exposure in transplant recipients than conventional trough (C0) monitoring,1–3 and many centers worldwide now routinely monitor CsA using C2 levels. Recommendations for the implementation of C2 monitoring were developed on the basis of early experience4 and have provided guidance to transplant clinicians in terms of CsA dose adjustments and C2 target ranges.
Since that time, C2 monitoring of CsA has been investigated further in large prospective trials,5, 6 and familiarity with C2 monitoring in the clinical setting has grown. The knowledge gained from this additional experience offers the opportunity to reassess initial recommendations for the implementation of C2 monitoring and to identify potential refinements in the liver transplant population.
This review addresses the use of C2 monitoring in the liver transplant patient during the early period after transplantation, based on an evaluation of the available data, and proposes an updated algorithm for CsA dose adjustments based on C2 monitoring.
AUC0–6, area under the curve for the first six hours post-dose; AUC0–12, area under the curve for the first twelve hours post-dose; C0, trough blood concentration; C2, blood concentration at 2 hours after dose; C4, blood concentration at 4 hours after dose; C6, blood concentration at 6 hours after dose; CsA, cyclosporine; ME, microemulsion; MMF, mycophenolate mofetil.
Why Use C2 Monitoring in Liver Transplantation?
A landmark study by Grant et al. in 19991 demonstrated that CsA exposure over the first 6 hours after dose correlated closely with freedom from rejection in de novo liver transplant patients. Similarly, peak concentration correlated well with risk of rejection, although C0 was not an accurate predictor of rejection risk. Time to peak concentration was found to occur at close to 2 hours after dose, such that C2 could be regarded as a surrogate marker for peak concentration. When the relationship between C2 and CsA exposure (area under the curve for the first six hours post-dose [AUC0–6]) was analyzed, C2 correlated closely with AUC0–6 (r = 0.93). Similarly, C2 correlated more closely with CsA exposure than trough level in maintenance liver transplant recipients.3
These results consistently indicated that C2 monitoring is a more effective strategy for measuring CsA exposure than C0 in liver transplantation and prompted two multicenter, prospective, randomized trials in which de novo liver transplant recipients receiving Neoral (CsA microemulsion, Novartis Pharma AG, Basel, Switzerland) were managed by C2 monitoring (i.e., dose adjustments were made on the basis of C2 levels). The first trial compared conventional C0 monitoring with C2 monitoring in 307 patients.5 At 3 months, the incidence of biopsy-proven acute rejection was lower with C2 monitoring (24% vs 32% with C0 monitoring), and the proportion of biopsy-proven episodes graded moderate or severe was significantly lower in the C2-monitored group (47% vs 73%, P = .01). The incidence and severity of adverse events was similar in both arms.
More recently, the LIS2T trial compared C2 monitoring of CsA vs tacrolimus with C0 monitoring in 499 de novo liver transplant recipients over the first 6 postoperative months.6 An interim analysis of 300 patients showed that the incidence of biopsy-proven acute rejection by 3 months was 28% among the CsA patients and 27% in those receiving tacrolimus (P = ns). The overall safety profile was equivalent in both treatment arms. However, patients receiving CsA had a significantly lower incidence of new-onset diabetes mellitus and diarrhea.
Using C2 monitoring of CsA in a steroid-free regimen also has been shown to result in a low rate of rejection (14% at 3 months) among de novo liver transplant patients receiving the anti-CD25 antibody basiliximab.7
Overall, the efficacy of C2 monitoring is excellent, with rejection rates ranging from 14% to 28% (Table 1),5–7 and is superior to results previously reported in studies using CsA C0 monitoring.8, 9 Moreover, in maintenance patients previously managed by C0 monitoring, adoption of C2 monitoring can identify patients overexposed to CsA. The resulting dose reductions can lead to significant improvements in renal function, blood pressure, and serum cholesterol.3, 10
Table 1. Early C2 Target Ranges and Incidence of BPAR for Trials of the Neoral Formulation of CsA Conducted in de Novo Liver Transplant Recipients
C2 Target Range 0–3 Months After Transplant (ng/mL)
Initially, it was thought that the same C2 range could be applied to all liver transplant patients, irrespective of particular patient characteristics or concomitant medication. There is a growing realization, however, that to provide the required level of exposure to CsA, the target C2 range should be adjusted according to the patient's risk of graft loss or predilection to adverse events and the intensity of adjunctive immunosuppressive therapy.
Guidance as to appropriate target levels is available from completed trials of C2 monitoring in liver transplantation (Table 1). Within a triple regimen comprising CsA–ME and steroids with or without azathioprine, a target range of 850–1400 ng/mL for the first 3 months after transplant achieved a 22% rate of acute rejection5; a slightly lower target range (800–1200 ng/mL) in a separate study resulted in a 3-month rejection rate of 28%.6 Target levels should be reduced progressively over the first year after transplant, and it has been proposed that a target level of 800 ng/mL (range 600–1000 ng/mL) after 6 months and 600ng/mL (range 500–700 ng/mL) after 1 year may be appropriate in patients receiving CsA and steroids.4 Among 104 liver transplant patients who initially received steroids with or without azathioprine and who were managed using C2 monitoring, mean C2 level was 763 ng/mL at 1 year after transplant, the incidence of acute rejection was 27%, mean serum creatinine was 118 μmol/L, and only 10% of patients still required azathioprine.11 Others have used a target range of 300–600 ng/mL in patients more than 1 year after transplant maintained on CsA.3
In patients receiving mycophenolate mofetil (MMF) because of an identified need for increased immunosuppression, it may be appropriate to use the same C2 target for MMF-treated patients as for those receiving azathioprine or dual therapy unless the MMF dose is high. When MMF is initiated to reduce CsA exposure in cases of CsA-related toxicity, reduced CsA dosing and C2 targets can be attempted. However, no trials of C2 monitoring have been carried out in MMF-treated liver transplant recipients to date or, indeed, those given sirolimus or everolimus.
Relative Importance of Attaining C2 Target Early
The effect of attaining target C2 level early in liver transplant recipients has been assessed in a comparative study of C2 vs C0 monitoring.5 In this study, a small number of patients (n = 16) reached the C2 target range of 850–1400 ng/mL by day 3, and incidence of rejection in this group was only 13%. The incidence was 26% among those attaining target C2 by day 7 and 34% for those patients who reached target by day 10. In the LIS2T study, in contrast, there was little difference in risk of rejection, regardless of when C2 range was achieved. It is important to note that the overall incidence of biopsy-proven acute rejection using CsA C2 monitoring in these studies (22–28%) was low compared with the literature (36–59%).8, 9, 12 This is despite the fact that one quarter of patients in the C2 vs C0 study and one third of those in the LIS2T trial did not reach C2 target until after day 7.
It thus appears less critical to achieve target C2 by day 3 or 5 after liver transplantation than had initially been believed.
Variation in Cyclosporine Absorption in the Early Posttransplant Period
Absorption of the Neoral formulation of CsA is relatively independent of bile flow and food consumption,13 and once a patient is stabilized on a dose, it generally does not need to be amended unless the target exposure changes. However, during the initial posttransplant period—and particularly during the first few days—the amount of CsA absorbed from a given dose can alter markedly. A number of factors can contribute to this situation, for example, recovery from paralytic ileus with consequent improvement of CsA absorption from the gut, improvement in graft function and cholestasis, or clamping of external biliary drainage.
Data from 250 patients managed by C2 monitoring of CsA within the LIS2T study demonstrate how C2 levels evolve during the first few weeks after transplant. The mean ratio of C2 achieved per 1 mg/kg/day over the first 3 months after transplant is shown in Fig. 1.14 There was a pronounced increase in the proportion of CsA measured in blood at 2 hours after dose, rising more than 4-fold by the end of the first month after transplantation. By the end of the second month, however, levels stabilized. Interestingly, it appears to take longer for absorption of CsA to stabilize in liver transplant recipients compared with renal transplant patients, in whom there is little change in the proportion of drug absorbed after the first month. In liver transplant patients, the time to peak concentration remains relatively stable in the early posttransplant period using the Neoral formulation of CsA, shortening only marginally from 2.2 hours at 10 days after transplant to 2.0 hours at 16 weeks.1 This suggests that the increasing C2:dose ratio over this period is at least partially caused by a genuine improvement in absorption from the gut, rather than solely a change in the shape of the absorption curve.
Clearly, this change in the C2 level achieved for a given dose must be taken into account when making dose adjustments early after transplant. Otherwise, improvements in absorption would risk the patient's overshooting target C2 level unexpectedly if a dose increase is made at a time when absorption is improving quickly.
Adjusting Dose of Cyclosporine
Previously, it was recommended4 that the dose of CsA be adjusted in direct proportion to the required change in C2 level. However, this strategy assumes that a constant proportion of the CsA dose is absorbed at all time points, whereas, in fact, absorption improves markedly during the initial posttransplant period, as previously mentioned. Thus, calculating a dose increase in proportion to the required C2 level could result in overshooting the C2 target range if the change in dose coincides with a pronounced improvement in CsA absorption not accounted for when calculating the new dose. Alternatively, patients may remain below target despite a proportional increase in dose if they are poor or delayed absorbers of CsA (see The Patient With Low C2 Values section later in this article) or if the initial dose of CsA they received was too low.
To minimize the risk of overexposure or underexposure to CsA, the following approach appears reasonable:
1Use an initial dose of CsA appropriate for the desired exposure level . For dual therapy or triple therapy with azathioprine, a starting dose of 10–15 mg/kg/day is suitable when patients can tolerate a full dose. Otherwise, a lower starting dose should be used and titrated upward on a daily basis as rapidly as possible, based on target levels and tolerability.
2Measure C2 level daily for the first week after transplant or until C2 values stabilize.
3Monitor C2 levels to detect a trend before increasing the dose; usually this will require measurements from 3 consecutive days. Once a trend is established, adjust the dose accordingly if required, taking into account improving CsA absorption (Fig. 2) when determining the new dose. If the C2 level exceeds target, reduce the dose immediately to avoid toxicity (Fig. 3).
4Continue to monitor C2 levels regularly once C2 values have stabilized. In the in-patient setting, C2 measurement 2 or 3 times a week is likely to be adequate. For outpatients, C2 levels should be measured at each routine clinic visit, for example twice a week for the first 2–3 weeks after discharge then weekly for the first 2 months. Reduce the CsA dose if C2 levels are above target. However, if a patient is below target, it may be useful to repeat the C2 measurement a few days later for confirmation before increasing the dose if there are no signs of rejection. Once CsA absorption has stabilized, it becomes appropriate to increase the dose in direct proportion to the desired change in C2 level.
The license for CsA microemulsion states a maximum dose of 10–15 mg/kg. Although in some patients, the physician may exceed this dose for specific reasons (e.g., in a patient shown to be a poor CsA absorber), keep in mind that liver transplant recipients given a dose of CsA above 20 mg/kg/day are at increased risk of CsA-related toxicity, particularly nephrotoxicity. It is unlikely that a dose greater than 20 mg/kg/day is necessary; patients who do not achieve C2 target with these doses may be delayed absorbers of CsA (see the next section) and would be overexposed to CsA with any further increase in dose.
The Patient With Low C2 Values
A proportion of patients do not show a trend toward achieving C2 target ranges, despite appropriate dosing during the first week after transplant. There are 2 possible reasons for this. First, the patient may be a poor absorber of CsA; this may be an inherent characteristic that will persist over the long term. More commonly, it may be the result of short-term limited absorption caused by slow recovery of normal gastrointestinal and hepatobiliary function after surgery. Second, the patient may be a “delayed” absorber of CsA, that is, with a long time to peak concentration such that C2 values remain low despite adequate total exposure to CsA (Fig. 4). Distinguishing between poor and delayed absorbers of CsA is critical because the management response differs.
If a patient continues to show a low C2 value by day 4 or 5 after transplant despite adequate CsA dose of between 10 and 15 mg/kg/day, blood CsA concentration should be measured at a later time point—usually C4 or C6. If the C4 or C6 value is lower than the C2 value, or if it is similar, the patient is a poor absorber of CsA, and a higher dose of CsA may be appropriate without compromising safety—up to a maximum of 20 mg/kg/day. The addition of another agent also may be helpful until the absorption of CsA reaches an appropriate level. In these poor absorbers of CsA, it is particularly important to monitor exposure closely, because a sudden improvement in absorption of CsA might result in overshooting the target and might require immediate dose reduction.
If, however, the C4 or C6 value is higher than C2, there is a late peak concentration, that is, the patient is a delayed absorber of CsA. In patients with this type of profile, the dose should be increased only with caution, and it is advisable to continue monitoring of both C2, and to check CsA exposure at a later time point (e.g., C4, C6, or even C0). Preliminary evidence suggests that delayed absorption may be a temporary phenomenon, at least in some patients. Therefore, repeated measurement at a later time point during follow-up will detect if a patient reverts to a more standard CsA absorption profile.
Minor Dose Adjustments
Over the duration of the 6-month LIS2T study, the mean number of dose adjustments per patient was 19 in the patients managed by CsA C2 monitoring (range 1–62), compared with 16 with tacrolimus (range 1–58).14 In some cases, the dose of CsA was repeatedly increased to a minor degree (e.g., 0.3 mg/kg/day or 5% of the total dose) then decreased to the same extent on successive days, which was unlikely to have affected C2 values significantly. Given that patients' absorption of CsA not only varies with time after transplant but also can be affected to a minor extent by food consumption15 on a day-to-day basis, frequent, minor dose modifications are not likely to be helpful. As familiarity with C2 monitoring increases, it is likely that the number of dose changes will decline with no penalty in terms of efficacy or safety.
Implementation of C2 Monitoring
Early involvement of ward, clinic, and laboratory staff is important when adopting C2 monitoring of CsA to ensure that samples are taken punctually and that results are reported promptly to allow for timely dose changes. There is a 15-minute window on either side of the 2-hour time point16 during which samples provide adequate accuracy. For in-patients, it can be convenient to administer the dose of CsA-ME 2 hours earlier than when C0 monitoring was used, such that the phlebotomist's schedule remains unchanged. Nursing staff should keep a record of the time that the CsA-ME dose is given to each patient, with the required time for C2 sampling, and the phlebotomist should then record the exact actual time that the sample is taken. The laboratory should be informed of the expected C2 range, such that laboratory staff can adopt and validate an appropriate dilution protocol. The assay system used does not need to be changed, and in contrast to C0 monitoring, C2 values are generally sufficiently consistent regardless of assay type because the level of CsA metabolites is lower with C2 monitoring. Within our own units, staffing requirements did not increase as a result of adopting C2 monitoring. Detailed recommendations have been developed for implementing C2 monitoring17 on the basis of the experience of several transplant centers.
C2 monitoring allows the dose of CsA to be individualized according to the absorption characteristics of each patient, which results in significant efficacy benefits while minimizing the risk of toxicity. The evidence now available indicates that C2 monitoring should be adopted routinely in de novo liver transplant recipients immunosuppressed with CsA and that it can achieve low levels of rejection with a favorable safety profile.6
Experience in recent clinical trials has led to refinements in early recommendations for dose management based on C2 values. First, inflexible adoption of dose increases in direct proportion to the required increase in C2 is likely to lead to overshooting of the C2 target because of the concurrent improvement in CsA absorption that occurs after liver transplantation. Instead, dose increases should be delayed until day 5 if a full starting dose of 10–15 mg/kg/day is used and should be undertaken when a trend in C2 level is apparent. Any dose increase should take into account increasing absorption. Fig. 5 illustrates a proposed strategy for dose adjustments during the first 2 weeks after liver transplantation.
Subsequently, C2 levels (and probably C4 or C6 in delayed absorbers) should be monitored regularly, and the dose should be adjusted according to the trend observed to remain within the target range.
Experience indicates that achieving C2 target within the first 3 or 5 days after transplant may be less necessary than formerly believed, which supports a more cautious approach to dose increases during the early posttransplant period. In particular, it is not advisable to increase the dose beyond 20 mg/kg/day without good reason.
In summary, as our understanding of C2 monitoring of the Neoral formulation of CsA has grown, it has become clear that a more flexible approach to its implementation, incorporating individual differences in CsA absorption, will enable us to retain the excellent clinical outcomes reported to date while reducing risk of toxicity still further.