Cyclosporine pharmacokinetics in nephrotic and kidney-transplanted children

The use of cyclosporine in dermatology: part II

Cyclosporine is highly effective in the treatment of a multitude of dermatoses. Concern over its side effect profile has limited its use in dermatology. Adverse effects are, for the most part, dose dependent and related to duration of therapy. Using the recommended monitoring protocols results in a significant decrease in the incidence of cyclosporine-related toxicities. This article provides a comprehensive review of the pharmacokinetics of cyclosporine, potential drug interactions, adverse effects, and recommendations for monitoring in patients treated with cyclosporine. The use of cyclosporine in pregnancy and in the pediatric population is also addressed.

LEARNING OBJECTIVES

After completing this learning activity, participants should be familiar with the monitoring guidelines of cyclosporine, its contraindications, its possible drug interactions, its adverse effect profile, and its use in pregnancy and the childhood and adolescent populations.

Population pharmacokinetics and Bayesian estimator of mycophenolic acid in children with idiopathic nephrotic syndrome

AIMS

To develop a population pharmacokinetic model for mycophenolic acid (MPA) in children with idiopathic nephrotic syndrome (INS) treated with mycophenolate mofetil (MMF), identify covariates that explain variability and determine the Bayesian estimator of the area under the concentration-time curve over 12 h (AUC(0-12)).

METHODS

The pharmacokinetic model of MMF was described from 23 patients aged 7.4 +/- 3.9 years (range 2.9-14.9) using nonlinear mixed-effects modelling (NONMEM) software. A two-compartment model with lag-time and first-order absorption and elimination was developed. The final model was validated using visual predictive check. Bayesian estimator was validated using circular permutation method.

RESULTS

The population pharmacokinetic parameters were apparent oral clearance 9.7 l h(-1), apparent central volume of distribution 22.3 l, apparent peripheral volume of distribution 250 l, inter-compartment clearance 18.8 l h(-1), absorption rate constant 5.16 h(-1), lag time 0.215 h. The covariate analysis identified body weight and serum albumin as individual factors influencing the apparent oral clearance. Accurate Bayesian estimation of AUC(0-12) was obtained using the combination of three MPA concentrations measured just before (T(0)), 1 and 4 h (T(1) and T(4)) after drug intake with a small error of 0.298 microg h(-1) ml(-1) between estimated and reference AUC(0-12).

CONCLUSIONS

The population pharmacokinetic model of MPA was developed in children with INS. A three-point (T(0), T(1) and T(4)h) Bayesian estimator of AUC(0-12) was developed and might be used to investigate the relation between MPA pharmacokinetic and pharmacodynamics in children with INS and determine if there is any indication to monitor MPA exposure in order to improve patient outcome based on individual AUC-controlled MMF dosing.

Population pharmacokinetic study of cyclosporine in patients with nephrotic syndrome

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

Calcineurin inhibitors in pediatric renal transplant recipients

The calcineurin inhibitors, cyclosporine (ciclosporin) [microemulsion] and tacrolimus, are the principal immunosuppressants prescribed for adult and pediatric renal transplantation. For pediatric patients, both drugs should be dosed per body surface area, and pharmacokinetic monitoring is mandatory. While monitoring of the trough levels may suffice for tacrolimus, cyclosporine therapy that utilizes the microemulsion formulation requires additional monitoring (e.g. determination of 2-hour post-dose levels). In a well designed randomized study in children, as in studies in adults, there was no difference in short-term patient and graft survival with cyclosporine microemulsion and tacrolimus. However, tacrolimus was significantly more effective than cyclosporine microemulsion in preventing acute rejection after renal transplantation when used in conjunction with azathioprine and corticosteroids. With regard to long-term outcome, the difference in acute rejection episodes resulted in a better glomerular filtration rate at 1 year after transplantation and eventually in better graft survival 4 years after renal transplantation. Whether this difference persists when calcineurin inhibitors are used in combination with mycophenolate mofetil has not been determined. The prevalence of hypomagnesemia was higher in the tacrolimus group whereas hypertrichosis and gingival hyperplasia occurred more frequently in the cyclosporine group. In contrast with adults, the incidence of post-transplantation diabetes mellitus was not significantly different between tacrolimus- and cyclosporine-treated patients. There was also no difference with regard to post-transplantation lymphoproliferative disorder. Medication costs were similar, but in view of the lower rejection episodes and better long-term graft survival as well as the more favorable cosmetic side effect profile, tacrolimus may be preferable. The recommendation drawn from the available data is that both cyclosporine and tacrolimus can be used safely and effectively in children. We recommend that cyclosporine should be chosen when patients experience tacrolimus-related adverse events.

Distribution of cyclosporin in organ transplant recipients

Cyclosporin is an immunosuppressive agent with a narrow therapeutic index. The total concentration of cyclosporin in blood is usually monitored to guide dosage adjustment and to compensate for substantial interindividual and intraindividual variability in cyclosporin pharmacokinetics. Cyclosporin is a highly lipophilic molecule and widely distributes into blood, plasma and tissue components. It mainly accumulates in fat-rich organs, including adipose tissue and liver. In blood, it binds to erythrocytes in a saturable fashion that is dependent on haematocrit, temperature and the concentration of plasma proteins. In plasma, it binds primarily to lipoproteins, including high-density, low-density and very-low-density lipoprotein, and, to a lesser extent, albumin. The unbound fraction of cyclosporin in plasma (CsA(fu)) expressed as a percentage is approximately 2%. It has been shown that both the pharmacokinetic and pharmacodynamic properties of cyclosporin are related to its binding characteristics in plasma. Furthermore, there is some evidence to indicate that the unbound concentration of cyclosporin (CsA(U)) has a closer association with both kidney and heart allograft rejection than the total (bound + unbound) concentration. However, the measurement of CsA(fu) is inherently complex and cannot easily be performed in a clinical setting. Mathematical models that calculate CsA(fu), and hence CsA(U), from the concentration of plasma lipoproteins may be a more practical option, and should provide a more accurate correlate of effectiveness and toxicity of this drug in transplant recipients than do conventional monitoring procedures. In conclusion, the distribution characteristics of cyclosporin in blood, plasma and various tissues are clinically important. Further investigations are needed to verify whether determination of CsA(U) improves the clinical management of transplant recipients.

[Passage from sandimmun to neoral in kidney transplantation in children]

BACKGROUND

The cyclosporine microemulsion formulation Neoral, which allows a better absorption and a more regular pharmacokinetic profile, is proposed for replacing the original formulation, Sandimmun. The present study reports the results of conversion from Sandimmun to Neoral in children with a kidney graft, a population for which information remains limited.

METHODS AND PATIENTS

Twenty children, 2.5 to 10.5 years of age, who had a kidney graft with a stable renal function for between six months to five years (m = 2.6) were the subjects of this study. The patients were switched from Sandimmun to Neoral at the same dose, adjusted afterwards on a cyclosporine trough level.

RESULTS

After six months, the mean dose decreased from 9.1 mg/kg/d to 8.4 mg/kg/d, i.e., 12.5%. After one year, the mean dose was 7 mg mg/kg/d, i.e., 28%. Of the 65% of patients who had a decreased dose, most of them had the highest dose of Sandimmun at the start. Mean serum creatininemia levels slightly increased from 85.6 to 89.5 mumol/L after six months (P = 0.03). None of the patients had a rejection crisis during the first six months under Neoral. Blood pressure did not change significantly, hirsutism improved in two cases but increased or appeared in two cases as well. Gingival hypertrophy increased or appeared in four cases.

DISCUSSION

A decrease in the dose was decided on either to maintain the trough CsA blood level in the desired range or because of the appearance of a symptom suggesting a side effect of cyclosporine, especially the increase of creatinemia. The trough level did not appear to be the best index for adapting the dose.

CONCLUSION

In stable pediatric kidney transplant recipients, the switch from Sandimmun to Neoral provided a reduction in drug dosage in 65% of cases without an increase in adverse events.

Cyclosporin pharmacokinetics in paediatric transplant recipients

Cyclosporin is an essential component of the antirejection drug protocol used in the long term management of paediatric organ transplant recipients. This article looks at the pharmacokinetics of cyclosporin in paediatric kidney, heart, liver and bone marrow transplant recipients and critically evaluates its relationship to pharmacokinetic data in adult transplant recipients. There are limited data on the pharmacokinetics of cyclosporin in paediatric transplant recipients (14 publications provide the database) as compared with the adult transplant population. Study design, analytical methodology and age ranges of the individuals differ between studies, making comparative interpretation of pharmacokinetic data difficult. However, significant trends are noteworthy and these may influence dose administration guidelines and therapeutic monitoring standards for cyclosporin in the paediatric organ transplant recipient. The bioavailability of the oral formulations of cyclosporin is highly variable as with the adult population, but there appears to be a correlation between cyclosporin bioavailability and age with both the traditional oral formulation (Sandimmun) and the new microemulsion formulation (Neoral) in young liver transplant patients. Bowel length, presystemic metabolism in the gut wall, type of transplant and time since transplant are contributing factors in the variation of bioavailability patterns in paediatric transplant patients. The volume of distribution of cyclosporin does not appear to differ between paediatric and adult transplant recipients, but systemic clearance is comparatively higher in the paediatric population. In general, paediatric patients require higher doses of cyclosporin to achieve target blood concentrations of the drug which are equivalent to the values used in the adult population. Younger patients (less than 8 years of age) may be managed more effectively with a 3 times daily administration schedule rather than the twice daily schedule which is universally used for cyclosporin in the transplant population. The comparatively higher doses and more frequent administration schedule used in paediatric transplant recipients are the consequence of age-related differences in bioavailability and the possibility of increased metabolic clearance of the drug in younger patients.