Pharmacokinetics of oral cyclosporine (Neoral) in heart transplant recipients during the immediate period after surgery

Optimal sampling time-point for cyclosporin A concentration monitoring in heart transplant recipients

The present study was performed to determine an optimal time-point for monitoring the concentration of the immunosuppressive drug cyclosporin A (CsA) in heart transplant patients and its efficacy in the prevention of transplant rejection. A total of 32 transplant recipients were randomly assigned for three treatment approaches. Recipients in groups A (n=11), B (n=13) and C (n=8) received oral administration of CsA at doses of 3.2, 3.5 and 4.4 mg/kg, respectively. The plasma CsA concentrations were examined at 2 h intervals over 12 h. Furthermore, their correlation with the 4 h pharmacokinetic profiles as the area under the plasma CsA concentration vs. time curve (AUC_{0-4 h}) were calculated The efficacy of CsA in inhibiting cardiac allograft rejection was assessed at 2 h after oral CsA intake (C2) and adverse events of the drug were examined in the C2-monitored recipients. The plasma CsA concentration rapidly increased in most recipients with a peak level detected at ~2 h after dosing. Regression analysis revealed that among all time-points assessed, the CsA had the highest correlation with the AUC_{0-4 h} at C2. At C2, increasing CsA doses exhibited a positive association with the measure of AUC_{0-4 h}. The efficacy of increasing CsA target levels at C2 in preventing heart transplant rejection was comparable, as the survival rate was 100% in all of the treatment groups. However, the proportion of recipients with side effects in group A was obviously lower than that in the other two groups. In conclusion, C2 is an ideal time-point for monitoring plasma CsA levels with a utility for individualising the next scheduled dose for each patient to ensure that target levels are maintained and achieve a high efficacy and safety of CsA therapy in heart transplant recipients (clinical trial no. 12002610).

Early Result of Heart Transplantation in Japan: Osaka University Experience

Since the new organ transplantation law was established in 1997, 17 heart transplantations have been performed in Japan, 7 of which were carried out at Osaka University Hospital. Recipient diagnosis was dilated cardiomyopathy in 2, dilated phase of hypertrophic cardiomyopathy in 4, and post-myocarditis cardiomyopathy in 1. Ages ranged from 8 to 49 years with a mean of 35.3 years. Five patients were bridged with a left ventricular assist device. The waiting period was 182–977 days (mean, 643 days). There was no early or late death during follow-up of 1–4.8 years. Under a standard triple-drug regimen using mycophenolate, there were 3 rejection episodes greater than grade 3 in 2 patients, and humoral rejection requiring plasmapheresis in one. A young boy whose donor was a hemodynamically compromised adult developed neurological sequelae after resuscitation following ventricular tachycardia. All patients were discharged and went back to work or their regular daily life. Although the donor shortage is still severe in Japan, the resumption of heart transplantation has been satisfactory, and left ventricular assist devices have played a crucial role.

Drug Interaction Between Oral Cyclosporine Modified and Iron

Objective: To describe a recent case of suspected interaction between oral cyclosporine modified and iron. Case Summary: A 33-year-old man underwent urgent cardiac transplantation for refractory cardiogenic shock caused by acute myocarditis. The patient had persistently low levels of cyclosporine despite a dose increase of the drug after the change of administration route from intravenous to oral. Spacing the administration of cyclosporine modified from oral iron resolved the problem. This drug interaction was reported as “probable” as determined by a Drug Interaction Probability Scale score of 7. Using this scoring system, the patient experienced a probable drug interaction between cyclosporine and iron both administered orally, and we surmise that the mechanism is that iron physicochemically destabilizes the cyclosporine microemulsion when both are administered concurrently. Discussion: This may be because of the interaction between cyclosporine microemulsion and iron because this cation can destabilize the immunosuppressant dosage form. Conclusions: Taking into account that joint administration of oral iron and cyclosporine modified can generate a physicochemical interaction that involves a decrease in the absorption of cyclosporine modified, we believe that it is necessary to recommend spacing administrations of both drugs as well as monitoring levels of cyclosporine in order to ensure optimal levels of immunosuppression.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

Serum amiodarone and desethylamiodarone concentrations following nasogastric versus oral administration

OBJECTIVE

Hospitalized patients unable to ingest anything by mouth require nutritional support by enteral feeding and administration of drugs through a nasogastric tube inserted into the digestive tract. Nasogastric administration of amiodarone may not always be equivalent to oral administration of amiodarone.

METHODS

We collected 162 observations of serum amiodarone and desethylamiodarone metabolite concentrations from 93 patients within 60 days of starting treatment with amiodarone. Eight patients were given the drug nasogastrically and 85 patients, orally. The two groups, were compared in terms of their serum concentration/(dose/weight) (C/D) value. A ratio of serum amiodarone concentration to serum desethylamiodarone concentration (AMD/DEA) was calculated for each sample. In addition, the percentage drug recovery after nasogastric administration of amiodarone was analysed.

RESULTS

Significant differences were observed in C/D values of amiodarone and desethylamiodarone and in AMD/DEA values of patients given amiodarone orally when compared with those given the drug nasogastrically. The C/D values of patients who received their medication nasogastrically were approximately 30% of the C/D values of patients who received their medication orally. Approximately 70% of the drug was recovered after it had passed through the nasogastric tube.

CONCLUSIONS

To achieve similar concentrations, an approximately 3-fold increase in dosage of amiodarone was required when patients were given the drug nasogastrically rather than orally. This suggests that the absorption of amiodarone following nasogastric administration is poor when compared with oral administration. Therapeutic drug monitoring is necessary to optimize dose particularly during the early stages of amiodarone therapy.

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.

Therapeutic drug monitoring of cyclosporine

The introduction of cyclosporine into clinical practice improved transplant outcome. However, the use of cyclosporine is not without problems. A narrow therapeutic index (the drug causes irreversible kidney damage when given in too high a dose) coupled with variable absorption and unpredictable pharmacokinetics has resulted in the need to measure cyclosporine blood concentrations to enable the dose of the drug to be individualised to the patient. When this is done correctly therapeutic efficacy can be maximised while toxicity is kept to a minimum. The evolution of cyclosporine dose optimisation started with the adjustment of empirical fixed doses by clinical "judgement;" progressed to therapeutic drug monitoring of trough, predose, C0 concentration with non specific assays that measured parent drug and metabolite; then on to "specific" cyclosporine C0 measurements; through area under curve monitoring using full profile measurements and limited sampling scheme procedures; and finally ending up with absorption profiling that targets AUC in the first 4 hours or the 2 hour blood cyclosporine concentration, C2. At the same time the formulation of cyclosporine has changed from Sandimmune to Neoral and now generic forms of the latter are available. The evidence base supporting C2 monitoring continues to grow and the technique will need to be customised as new combination therapies emerge. Therapeutic drug monitoring of cyclosporine may also need to be tailored to avoid the potential negative impact of switching patients to generic forms of the drug.

Calcineurin inhibitors in heart transplantation

The use of calcineurin inhibitors (CNIs; cyclosporine and tacrolimus) has dramatically increased medium-term life expectancy after heart transplantation but has had only limited impact on long-term outcomes for heart transplant recipients. The original oil-based formulation of cyclosporine has been superceded by a microemulsion formulation (Neoral), which has more predictable pharmacokinetics and allows more precise dose-tailoring. Cyclosporine microemulsion and tacrolimus (Prograf) have a similar efficacy in the prevention of acute rejection of heart transplants, but their use is accompanied by nephrotoxicity and by cardiovascular side effects. The efficacy of immunosuppression can be improved by adjunctive therapy, such as azathioprine, mycophenolate mofetil (MMF; Cellcept), corticosteroids, and induction therapy. One of the most important predictors of patient mortality at >5 years after heart transplantation is cardiac allograft vasculopathy (CAV)/late graft failure, which accounts for 31% of deaths. Neither cyclosporine nor tacrolimus have been shown to prevent the development of CAV. In terms of efficacy, MMF provides a modest advantage over azathioprine in preventing CAV, and the combination of cyclosporine plus MMF results in significantly lower mortality than cyclosporine plus azathioprine. Overall, CNIs have multiple cardiovascular side effects, such as hypertension, hyperlipidemia and new-onset diabetes after transplantation, although cyclosporine and tacrolimus have somewhat different cardiovascular side-effect profiles. The challenge in choosing the best immunosuppressive regimen is to balance efficacy and safety to optimize graft and patient survival over the course of many decades. Because cyclosporine and tacrolimus have similar efficacy against acute rejection the choice of CNI for heart transplant recipients should be based on the relative risk of cardiovascular and renal side effects.

Optimizing the immunosuppressive regimen in heart transplantation

The use of immunosuppression regimens containing a calcineurin inhibitor (CNI), an adjunct immunosuppressant (e.g., azathioprine, everolimus or mycophenolate mofetil) and corticosteroids has effectively reduced the risk of early graft loss due to acute rejection in heart transplant recipients. At present, late graft loss due to cardiac allograft vasculopathy (CAV) remains a major challenge for transplant teams. CAV is characterized by intimal hyperplasia as a result of endothelial cell injury. Factors relating to the transplant procedure itself (e.g., ischemic time and reperfusion injury), cardiovascular risks (e.g., donor age, hypertension, hyperlipidemia, pre-existing diabetes and new-onset diabetes after transplantation), immunologic risks (e.g., acute rejection episodes, anti-HLA antibodies) and the side effects of immunosuppression with CNIs or corticosteroids (e.g., cytomegalovirus infection, nephrotoxicity) have all been implicated in the development of CAV. The 2 main approaches to the prevention of CAV are modification of underlying risk factors (e.g., treatment with anti-hypertensive agents and lipid-lowering drugs, and optimizing the immunosuppressive regimen) and improvement in immunosuppression. CNIs remain the cornerstone of immunosuppressive regimens in heart transplantation, but new parameters for monitoring CNI exposure and new immunosuppressive regimens hold the promise of reduced overall CNI exposure with consequent reductions in vascular toxicity and improved clinical outcomes. Traditionally, trough levels of cyclosporine (C(0)) have been used to monitor exposure to cyclosporine and to assess the need for dose adjustment. However, optimal cyclosporine exposure can now be achieved through monitoring of cyclosporine levels 2 hours after dosing (C(2) monitoring). Furthermore, in a pivotal trial in heart transplantation, the new proliferation signal inhibitor, everolimus, plus full-dose cyclosporine and corticosteroids, has been shown to have improved impact on prevention of biopsy-proven acute rejection (and other efficacy end-points) and longer term on the prevention of CAV. In addition, there is evidence from studies in renal transplant recipients that everolimus plus reduced exposure cyclosporine is effective and well tolerated-with the regimen having a reduced potential for CNI-related nephrotoxicity and for other CNI-related cardiovascular side effects.

Experience with conversion from sandimmun to neoral cyclosporine and the correlation of c2 levels with renal function

Pharmacologic monitoring of the cyclosporine microemulsion Neoral is an important tool to improve the efficacy and to avoid toxicity of the drug. Recent trials have shown that the absorption profiling tools represented by the area under the time-concentration curve from 0 to 4 hours postdose and concentration 2 hours postdose (C2) levels are the best predictors of acute rejection in the early posttransplant period. Since similar data regarding maintenance immunosuppression are scarce, we report our experience on Neoral C2 monitoring in renal transplant recipients during the late posttransplant period. However, available data on optimal Neoral C2 levels in the late posttransplantation period are scant and have not been correlated with well-defined endpoints such as chronic allograft nephropathy.

Inhibitors of Calcineurin

Before the early 1980s, patient and allograft survival for solid organ transplant recipients was dismal. By 1983, the first calcineurin blocker, cyclosporine (Sandimmun), had been introduced, and outcomes were dramatically improved. However, cyclosporine macroemulsion had suboptimal pharmacokinetics, significant drug interactions, and several adverse effects, including nephrotoxicity, neurotoxicity, hyperlipidemia, and hypertension. Recent advances with cyclosporine include the introduction of modified dosage formulations: Neoral, a microemulsion, and several generic microemulsion products. The potent second-generation calcineurin blocker tacrolimus (Prograf) was introduced in 1994 and has become the drug of choice for several types of transplant recipients. Although tacrolimus has improved pharmacokinetics and therapeutic drugmonitoring parameters, it has adverse effects such as nephrotoxicity, neurotoxicity, and diabetes. Thus, current immunosuppressive regimens implementing calcineurin blockers often involve additional immunosuppressive agents to “spare” the use of these agents, minimizing their adverse effects. This article reviews the mechanisms of action, pharmacokinetics, clinical use, therapeutic drug monitoring, drug interactions, adverse effects, and dosing of cyclosporine and tacrolimus in solid organ transplant recipients.