Pharmacokinetics of sirolimus in stable renal transplant patients after multiple oral dose administration

Correlation between pretransplantation test dose cyclosporine pharmacokinetic profiles and posttransplantation sirolimus blood levels in renal transplant recipients

We sought to determine whether pretransplantation test dose pharmacokinetic measurements of cyclosporine (CsA) concentrations would forecast the posttransplantation blood concentrations of sirolimus in renal transplant patients treated de novo with CsA, sirolimus, and prednisone. All 44 renal transplant recipients enrolled in Phase I/II studies of de novo posttransplantation therapy with sirolimus, CsA, and prednisone underwent pretransplantation pharmacokinetic profiling after having received paired intravenous (i.v.) and oral test doses of CsA. After transplantation, all patients were treated with CsA on a once- or twice-daily schedule (according to a concentration-controlled regimen), with tapering doses of prednisone, and with fixed doses of sirolimus on a once-daily schedule. Patients were divided into four cohorts based on the deviation of their pretransplantation CsA clearance or bioavailability values from the mean. Patients with high pretransplantation CsA clearance rates displayed a significantly lower mean posttransplantation value of sirolimus trough concentrations than patients with low pretransplantation CsA clearance rates. In contrast, values for pretransplantation absolute oral CsA bioavailability failed to correlate with the mean posttransplantation concentration of sirolimus but did predict posttransplantation CsA bioavailability. Therefore, pretransplantation CsA clearance rate estimates may forecast posttransplantation sirolimus concentrations, possibly guiding use of sirolimus therapy to achieve an optimal ratio of concentration-dependent immunosuppressive versus toxic effects.

Simultaneous on-line extraction and analysis of sirolimus (rapamycin) and ciclosporin in blood by liquid chromatography-electrospray mass spectrometry

We developed a sensitive and specific semi-automated liquid chromatography-electrospray mass spectrometric (HPLC-ESI-MS) assay for the simultaneous quantification of sirolimus and ciclosporin in blood. Following a simple protein precipitation step, the supernatants were injected into the HPLC system and extracted on-line. After column switching, the analytes were backflushed from the extraction column onto the analytical narrow-bore column and eluted into the ESI-MS system. The assay was linear from 0.4 to 100 microg/l sirolimus and from 2 to 1500 microg/l ciclosporin. The mean recoveries of sirolimus and ciclosporin were 98 and 96%, respectively. The mean interday precision/accuracy was 8.6%/-4.8% for sirolimus and 9.3%/-2.9% for ciclosporin.

Quantitative analysis of sirolimus (Rapamycin) in blood by high-performance liquid chromatography-electrospray tandem mass spectrometry

We report here a quantitative method for the analysis of sirolimus in blood using solid-phase sample preparation and HPLC-electrospray-tandem mass spectrometry detection. Blood samples (500 microl) were prepared by pre-treatment with acetonitrile: 15 mM zinc sulphate (70:30, v/v), containing 32-demethoxysirolimus (internal standard) and C18 solid-phase extraction. The electrospray conditions were chosen to enhance the [M+NH4]+ species at the expense of other species. Detection was by multiple reactant monitoring with the mass transitions m/z 931.8-->864.6 and m/z 901.8-->834.4 employed for sirolimus and the internal standard, respectively. The method was linear over the range 0.2 to 100.0 microg l(-1). The accuracy and inter-day precision, over this concentration range, was 94.4% to 104.4% and 1.4% to 5.0%, respectively. The accuracy and total precision at the limit of quantitation (0.2 microg l(-1)) was 103.0% and 10.8%, respectively. The mean absolute recovery of sirolimus and the internal standard were 80.5% and 81.3%, respectively. The sensitivity and analytical concentration range of the method make it suitable for therapeutic drug monitoring and pharmacokinetic studies. Further, the ability of the method to measure parent drug specifically will facilitate the evaluation of immunoassays for sirolimus.

Immunosuppressive effects and safety of a sirolimus/cyclosporine combination regimen for renal transplantation

BACKGROUND

Sirolimus, a novel immunosuppressant that inhibits cytokine-driven cell proliferation and maturation, prolongs allograft survival in animal models. After a phase I trial in stable renal transplant recipients documented that cyclosporine and sirolimus have few overlapping toxicities, we conducted an open-label, single-center, phase I/II dose-escalation trial to examine the safety and efficacy of this drug combination.

METHODS

Forty mismatched living-donor renal transplant recipients were sequentially assigned to receive escalating initial doses of sirolimus (0.5-7.0 mg/m2/day), in addition to courses of prednisone and a concentration-controlled regimen of cyclosporine. We conducted surveillance for drug-induced side effects among sirolimus-treated patients and compared their incidence of acute rejection episodes as well as mean laboratory values with those of a historical cohort of 65 consecutive, immediately precedent, demographically similar recipients treated with the same concentration-controlled regimen of cyclosporine and tapering doses of prednisone.

RESULTS

The addition of sirolimus reduced the overall incidence of acute allograft rejection episodes to 7.5% from 32% in the immediately precedent cyclosporine/prednisone-treated patients. At 18- to 47-month follow-up periods, both treatment groups displayed similar rates of patient and graft survival, as well as morbid complications. Although sirolimus-treated patients displayed comparatively lower platelet and white blood cell counts and higher levels of serum cholesterol and triglycerides, sirolimus did not augment the nephrotoxic or hypertensive proclivities of cyclosporine. The degree of change in the laboratory values was more directly associated with whole blood trough drug concentrations than with doses of sirolimus.

CONCLUSIONS

Sirolimus potentiates the immunosuppressive effects of a cyclosporine-based regimen by reducing the rate of acute rejection episodes.

Metabolism and drug interactions of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in transplant patients: are the statins mechanistically similar?

3-Hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.88) inhibitors are the most effective drugs to lower cholesterol in transplant patients. However, immunosuppressants and several other drugs used after organ transplantation are cytochrome P4503A (CYP3A, EC 1.14.14.1) substrates. Pharmacokinetic interaction with some of the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, specifically lovastatin and simvastatin, leads to an increased incidence of muscle skeletal toxicity in transplant patients. It is our objective to review the role of drug metabolism and drug interactions of lovastatin, simvastatin, pravastatin, fluvastatin, atorvastatin, and cerivastatin. In the treatment of transplant patients, from a drug interaction perspective, pravastatin, which is not significantly metabolized by CYP enzymes, and fluvastatin, presumably a CYP2C9 substrate, compare favorably with the other statins for which the major metabolic pathways are catalyzed by CYP3A.

Rapamycin: personal algorithms for use based on 250 treated renal allograft recipients

RAPA represents a likely candidate for addition to the maintenance immunosuppressive regimen, for it seems to potentiate markedly the efficacy fo CyA-based therapy. RAPA reduces the incidence of acute rejection episodes; indeed, it may even be useful to disrupt ongoing steroid- and antibody-resistant cellular and humoral acute rejection reactions. Some data in model systems, both in vitro and in vivo, suggest that RAPA may afford prophylaxis against chronic rejection. The enhanced immunosuppression is likely to permit reduction in CyA doses/concentration, thereby mitigating its nephrotoxic effects, and to permit withdrawal of corticosteroids, providing relief from their osteopenic, myopathic, and metabolic effects. As with other potent immunosuppressives, RAPA causes a range of adverse side effects, most importantly myelosuppression and hyperlipidemia. Hypothesis-testing investigations are already underway to elucidate the mechanisms of the adverse effects so as to design strategies to minimize their impact on posttransplant morbidity.

Rapamycin: distribution, pharmacokinetics and therapeutic range investigations: an update

Based on the findings above, a number of conclusions can be made regarding the distribution, pharmacokinetics, and therapeutic range investigations with RAPA: (a) the majority of the drug is sequestered in erythrocytes, resulting in whole blood concentrations being considerably higher than plasma concentrations; (b) the drug is metabolized by the same cytochrome P450 3A enzyme involved in the metabolism of CsA and FK506. Metabolites are primarily simple demethylations and hydroxylations with 41-O-demethyl RAPA being the major metabolite both in vivo and in vitro; (c) the drug has a relatively long half-life in both humans and animals with 24-h trough concentrations being within the analytical range of HPLC when immunosuppressive doses are administered; (d) the drug exhibits a degree of proportionality between trough concentrations and dose; (e) a strong correlation exists between area under the concentration-time curve and trough blood concentration at steady state; (f) trough concentrations of the drug appear to be related to immunosuppressive efficacy and drug-related side effects; (g) the nephro- and neurotoxic properties of CsA are not augmented by concurrent treatment with RAPA; and (h) phase IIB trial results have shown a decrease of acute rejection episodes from 40% to < 10% among patients treated with full-dose CsA plus RAPA. The studies described here should provide a basis for the establishment of therapeutic monitoring protocols for RAPA. In addition, new derivatives of RAPA, such as SDZ RAD, designed to overcome formulation problems associated with RAPA, while maintaining similar pharmacokinetics and in vivo activity, show promise as alternatives to RAPA.

The effects of relative timing of sirolimus and cyclosporine microemulsion formulation coadministration on the pharmacokinetics of each agent

INTRODUCTION

Sirolimus and cyclosporine (INN, ciclosporin) share the same cytochrome P4503A metabolic pathways, and both drugs are substrates for p-glycoprotein countertransport. These factors most likely affect the bioavailability of both drugs. This study served to examine whether the timing of the administration of cyclosporine and sirolimus might significantly affect the relative bioavailability of one or both of these drugs.

METHODS

In this randomized crossover trial, 24 stable kidney transplant recipients who were treated after transplant with a combination of sirolimus, cyclosporine, and prednisone for at least 3 months before study initiation, received individualized doses of sirolimus once daily and cyclosporine in the microemulsion formulation twice a day. A total of 20 patients completed the full crossover design. Patients were randomized to one of two dosing schedules: 10 of the patients who completed the study received the morning doses of sirolimus and cyclosporine concomitantly for the first 7 days (schedule I), and from days 8 to 14 the sirolimus dose was administered 4 hours after the morning cyclosporine dose. Ten of the patients received the sirolimus dose 4 hours after the morning cyclosporine dose for the first 7 days (schedule II), and from days 8 to 14 they received concomitant morning doses of cyclosporine and sirolimus. Pharmacokinetic profiles of sirolimus and cyclosporine performed on all patients on days 7, 14, and 15 yielded the area under the concentration-time curve (AUC), peak concentration (Cmax), time to Cmax (tmax), trough cyclosporine concentration (Co), and trough sirolimus concentration (Co) values.

RESULTS

Sirolimus AUC and sirolimus trough levels were consistently and significantly higher when both cyclosporine and sirolimus were administered concomitantly than when they were administered 4 hours apart. No effect attributable to timing of drug administration could be found on cyclosporine pharmacokinetic parameters.

CONCLUSION

This study shows that the relative timing of administration of cyclosporine and sirolimus significantly affects the blood concentrations of sirolimus.