Therapeutic drug monitoring of sirolimus: correlations with efficacy and toxicity

An open prospective pilot study on the use of rapamycin after penetrating high-risk keratoplasty

BACKGROUND

The purpose of this study was to prove efficacy and safety of systemic immunosuppression with rapamycin following penetrating high-risk keratoplasty. Rapamycin has shown its immunosuppressive potential in the rat keratoplasty model and is a component of several immunosuppressive protocols after solid organ transplantation. In this pilot study, we compared the efficacy and safety of rapamycin and mycophenolate mofetil (MMF).

METHODS

Ten patients (group 1) undergoing high-risk keratoplasty were included in this study, receiving rapamycin as postoperative immunoprophylaxis. Rapamycin was administered orally once daily (blood trough level 4-10 ng/ml) for 6 months. Thereafter, it was tapered over 2 weeks. The control group (group 2) consisted of 24 patients who received 1000 mg MMF twice daily for 6 months. All of the patients received postoperative medication with fluocortolone 1 mg/kg/day (tapered over 3 weeks) and prednisolone acetate eyedrops 5 times per day (tapered over 5 months).

RESULTS

Mean follow-up of all patients (n=34) was 739 days. No immune reaction was observed in groups 1 and 2 during the first 6 months under immunosuppression. Two immune reactions occurred in group 1, and five in group 2 within a 2-year follow-up. All of the immune reactions were reversible. The side effects observed in both groups were mostly reversible.

CONCLUSIONS

Rapamycin and mycophenolate mofetil seem to be similarly efficacious in preventing immune reactions after high-risk keratoplasty, as long as they are administered. However, we observed a broad spectrum of side effects from rapamycin.

Comparison of the Reintroduced MEIA® Assay With HPLC-MS/MS for the Determination of Whole-Blood Sirolimus From Transplant Recipients

Therapeutic monitoring with dosage individualization of sirolimus drug therapy is standard clinical practice for organ transplant recipients. For several years sirolimus monitoring has been restricted as a result of lack of an immunoassay. The recent reintroduction of the microparticle enzyme immunoassay (MEIA) for sirolimus on the IMx analyser has the potential to address this situation. This study, using patient samples, has compared the MEIA sirolimus method with an established HPLC-tandem mass spectrometry method (HPLC-MS/MS). An established HPLC-UV assay was used for independent cross-validation. For quality control materials (5, 11, 22 microg/L), the MEIA showed acceptable validation criteria based on intra- and inter-run precision (CV) and accuracy (bias) of <8% and <13%, respectively. The lower limit of quantitation was found to be approximately 3 microg/L. The performance of the immunoassay was compared with HPLC-MS/MS using EDTA whole-blood samples obtained from various types of organ transplant recipients (n = 116). The resultant Deming regression line was: MEIA =1.3 x HPLC-MS/MS + 1.3 (r = 0.967, S(y/x) = 1) with a mean bias of 49.2% +/- 23.1% (range, -2.4% to 128%; P<0.001). The reason for the large and variable bias was not explored in this study, but the sirolimus-metabolite cross-reactivity with the MEIA antibody could be a substantive contributing factor. Whereas the MEIA sirolimus method may be an adjunct to sirolimus dosage individualization in transplant recipients, users must consider the implications of the substantial and variable bias when interpreting results. In selected patients where difficult clinical issues arise, reference to a specific chromatographic method may be required.

Sirolimus: the evidence for clinical pharmacokinetic monitoring

This review seeks to apply a decision-making algorithm to establish whether clinical pharmacokinetic monitoring (CPM) of sirolimus (rapamycin) in solid organ transplantation is indicated in specific patient populations. The need for CPM of sirolimus, although a regulatory requirement in Europe, has not yet been firmly established in North America and other parts of the world. Sirolimus has demonstrated immunosuppressive efficacy in renal, pancreatic islet cell, liver and heart transplant recipients. The pharmacological response of immunosuppressive therapy with sirolimus cannot be readily evaluated; however, a relationship between trough blood sirolimus concentrations, area under the plasma concentration-time curve (AUC) and the incidence of rejection has been proposed. Furthermore, sirolimus can be measured in whole blood by several assays--high-performance liquid chromatography with detection by tandem mass spectrometry, or with ultraviolet detection, radioreceptor assay or microparticle enzyme immunoassay. Both experimental animal and clinical data suggest that adverse events and their associated severity are correlated with blood concentrations. To prevent rejection and minimise toxicity, a therapeutic range of 4-12 microg/L (measured via chromatographic assays) is recommended when sirolimus is used in conjunction with ciclosporin. If ciclosporin therapy is discontinued, a target trough range of 12-20 microg/L is recommended. Sirolimus pharmacokinetics display large inter- and intrapatient variability, which may change in specific patient populations due to disease states or concurrent immunosuppressants or other interacting drugs. Due to the long half-life of sirolimus, dosage adjustments would ideally be based on trough levels obtained more than 5-7 days after initiation of therapy or dosage change. Once the initial dose titration is complete, monitoring sirolimus trough concentrations weekly for the first month and every 2 weeks for the second month appears to be appropriate. After the first 2 months of dose titration, routine CPM of sirolimus is not necessary in all patients, but may be warranted to achieve target concentrations in certain populations of patients, but the frequency of further monitoring remains to be determined and should be individualised.

Pharmacogenetics in Transplant Patients

Pharmacogenetics holds the potential to allow individualized dosing of immunosuppressive agents to optimize their therapeutic effect while minimizing adverse effects. As more pharmacogenetic information accumulates, the prospect of reducing or discontinuing the intensive therapeutic drug monitoring of immunosuppressants looks attractive. However, the long process of developing useful clinical information from basic information on the genes of interest is at a very early stage, and our present information does not supercede pharmacokinetic or blood concentration monitoring of immunosuppressants. The most extensive blood concentration/dose information available is on tacrolimus and its dosing related to CYP3A5 and ABCB1 gene polymorphisms. Although CYP3A5 genotype is definitely associated with tacrolimus dosing, the only recommendation presently published is for an arbitrary doubling of the starting tacrolimus dose in CYP3A5 expressors. For cyclosporine, sirolimus, and corticosteroids, the presently available pharmacogenetic information does not permit pharmacokinetic predictions. The pharmacodynamics of immunosuppressants, as evidenced by effects on acute rejection or adverse drug effects, have considerably more potential for prediction by pharmacogenetic models. Drug-resistant rejection, nephrotoxicity, steroid resistance and osteonecrosis, and even patient survival may ultimately be predicted by models incorporating multiple gene polymorphisms and other critical patient information. At this point, treatment algorithms can be developed that will allow us to individualize a transplant patient's immunosuppressive therapy.

Sirolimus and tacrolimus trough concentrations and dose requirements after kidney transplantation in relation to CYP3A5 and MDR1 polymorphisms and steroids

BACKGROUND

CYP3A5 and MDR1 polymorphisms have been shown to influence tacrolimus blood concentrations and dose requirements. The aim is to determine whether these polymorphisms also affect sirolimus trough concentrations and dose requirements after kidney transplantation.

METHODS

Eighty-five renal transplant recipients receiving sirolimus were included. Twenty-four were treated with a combined sirolimus-tacrolimus regimen. Eighty-one patients received steroids. Sirolimus and tacrolimus were adjusted to a target therapeutic window. CYP3A5 (intron 3) and MDR1 (exons 12, 21, 26) genotypes were correlated to the adjusted trough concentrations and dose requirements for both sirolimus and tacrolimus.

RESULTS

There were no significant correlation between adjusted sirolimus trough concentrations or dose requirements and genetic polymorphisms. In a multiple regression model, adjusted-prednisone dose was involved with a positive or negative effect when considering sirolimus dose requirements or adjusted concentrations, respectively. In the subgroup of patients treated by tacrolimus and sirolimus, adjusted tacrolimus doses were higher in patients carrying at least one CYP3A5 *1 allele (median 0.083 vs. 0.035 mg/kg for CYP3A5*3/*3 patients, P<0.05). Adjusted-prednisolone dose and CYP3A5 polymorphism explained up to 61% of the variability in tacrolimus dose requirements.

CONCLUSIONS

Unlike tacrolimus, sirolimus adjusted trough concentrations and dose requirements seem not affected by CYP3A5 and MDR1 polymorphisms. Adjusted-prednisone dose has a significant impact on tacrolimus and sirolimus dose requirements.

Relationship of cyclosporin and sirolimus blood concentrations regarding the incidence and severity of hyperlipidemia after kidney transplantation

The influence of drug concentrations on the development of persistent posttransplant hyperlipidemia was investigated in 82 patients who received cyclosporin A (CsA) and prednisone plus sirolimus (SRL) (52) or azathioprine (AZA) (30) during the first year after transplantation. Blood levels of CsA and SRL, daily doses of AZA and prednisone, and cholesterol, triglyceride, and glucose concentrations were determined during each visit (pretransplant and 30, 60, 90, 120, 180, and 360 days posttransplant). Persistent hyperlipidemia was defined as one-year average steady-state cholesterol (CavCHOL) or triglyceride (CavTG) concentrations above 240 and 200 mg/dL, respectively. Mean cholesterol and triglyceride concentrations increased after transplantation (P < 0.01) and were higher in patients receiving SRL compared to AZA (P < 0.001). Patients receiving SRL showed a significantly higher number of cholesterol (> 229 or > 274 mg/dL) and triglyceride (> 198 or > 282 mg/dL) determinations in the upper interquartile ranges. CsA and SRL interquartile ranges correlated with cholesterol concentrations (P = 0.001) whereas only SRL interquartile ranges correlated with triglyceride concentrations (P < 0.0001). Only pretransplant cholesterol concentration > 205 mg/dL was independently associated with development of persistent hypercholesterolemia (CavCHOL > 240 mg/dL, relative risk (RR) = 20, CI 3.8-104.6, P = 0.0004) whereas pretransplant triglyceride concentration > 150 mg/dL (RR = 7.2, CI 1.6-32.4, P = 0.01) or > 211 mg/dL (RR = 19.8, CI 3.6-107.9, P = 0.0006) and use of SRL (RR = 3, CI 1.0-8.8, P = 0.0049) were independently associated with development of persistent hypertriglyceridemia (CavTG > 200 mg/dL). Persistent hypercholesterolemia was more frequent among patients with higher pretransplant cholesterol concentrations and was dependent on both CsA and SRL concentrations. Persistent hypertriglyceridemia was more frequent among patients with higher pretransplant triglyceride concentrations and was dependent on SRL concentrations.

Sirolimus: Its role in nephrology (Review Article)

Sirolimus (Rapamycin, Wyeth Pharmaceuticals Australia Pty Ltd, Baulkham Hills, NSW, Australia) (SRL) has received increasing attention as an immunosuppressant in renal and other solid organ transplantation. Sirolimus is the first marketed agent in a new class of drugs with a novel mechanism of action. Sirolimus binds, like tacrolimus, to a member of the FK binding protein (FKBP) family. The SRL/FKBP complex binds to the protein kinase mTOR. Binding to mTOR blocks activation of signal transduction pathways causing arrest of the cell cycle in the G1 phase. It is now known that mTOR is a central regulator of cell growth and proliferation. The immunosuppressive properties of SRL are due primarily to blockade of interleukin-2 (IL-2)-induced proliferation of T cells. There is still much to be learnt about how best to use the drug. The key advantage over the current choice of immunosuppressive agents is the ability to preserve renal function and pathology while producing excellent rejection-free, graft survival rates. Thus, SRL may find its pivotal role as a calcineurin inhibitors replacement in patients whose grafts are affected by chronic allograft nephropathy. A second major driver for use may prove to be the impact of SRL on cancer incidence and prognosis. Studies still need to be performed to evaluate the best timing for commencement of SRL and the optimal dosage to minimize side-effects.

Effects of calcineurin inhibitors on sirolimus pharmacokinetics during staggered administration in renal transplant recipients

STUDY OBJECTIVE

To compare the effects of different calcineurin inhibitors on sirolimus pharmacokinetics during long-term, staggered administration in kidney transplant recipients. Design. Randomized, open-label, parallel-group trial.

SETTING

A medical center and one of its teaching hospitals in Taiwan.

PATIENTS

Twenty-two de novo kidney transplant recipients.

INTERVENTION

Patients received cyclosporine microemulsion or tacrolimus capsules twice/day in combination with once-daily sirolimus solution and corticosteroids. Sirolimus was administered 6 hours after the morning dose of cyclosporine or tacrolimus. After receiving a 6-mg loading dose of sirolimus, participants received sirolimus 2 mg/day for at least 7 days. Neither the cyclosporine nor the tacrolimus dosage was adjusted for at least 3 days before and during blood sampling for pharmacokinetic profiling.

MEASUREMENTS AND MAIN RESULTS

One patient dropped out because of trimethoprim-sulfamethoxazole-related hepatotoxicity. We observed no differences between the two patient groups in terms of their demographic data, renal and liver function, or dosage of sirolimus during the study. During multiple-dose administration, the area under the whole-blood concentration-time curve and the peak and trough concentrations of sirolimus in the cyclosporine group were, respectively, 1.46 (95% confidence interval [CI] 1.21-1.71), 1.42 (95% CI 1.08-1.76), and 1.42 (95% CI 1.09-1.76) times higher than those of the tacrolimus group, even though sirolimus was administered 6 hours after the other agents.

CONCLUSION

Sirolimus pharmacokinetics may change significantly when calcineurin inhibitors are switched, even with staggered administration, which may not completely prevent a drug interaction between cyclosporine and sirolimus solution.

Clinical application of sirolimus in renal transplantation: an update

In addition to an analysis of the final results of phase I/II and phase III clinical trials of sirolimus (SRL), this review focuses on the recent results of several studies in renal transplantation, which include diverse combinations of SRL with other immunosuppressive agents. While SRL was initially introduced as an adjunctive agent to calcineurin inhibitors, it is now serving as the base for therapies that spare or avoid these nephrotoxic drugs. However, to optimize the use of SRL as base therapy, further work is necessary to determine target concentrations, requirement for concomitant steroids and/or nucleoside synthesis blockers, and countermeasure therapy to overcome the drug's adverse effects.

CEDIA® Sirolimus Assay Compared With HPLC-MS/MS and HPLC-UV in Transplant Recipient Specimens

The role of the therapeutic drug monitoring laboratory in support of immunosuppressant drug therapy is well established, and the introduction of sirolimus (SRL) is a new direction in this field. The lack of an immunoassay for several years has restricted the availability of SRL assay services. The recent availability of a CEDIA SRL assay has the potential to improve this situation. The present communication has compared the CEDIA SRL method with 2 established chromatographic methods, HPLC-UV and HPLC-MS/MS. The CEDIA method, run on a Hitachi 917 analyzer, showed acceptable validation criteria with within-assay precision of 9.1% and 3.3%, and bias of 17.1% and 5.8%, at SRL concentrations of 5.0 microg/L and 20 microg/L, respectively. The corresponding between-run precision values were 11.5% and 3.3% and bias of 7.1% and 2.9% at 5.0 microg/L and 20 microg/L, respectively. The lower limit of quantification was found to be 3.0 microg/L. A series of 96 EDTA whole-blood samples predominantly from renal transplant recipients were assayed by the 3 methods for comparison. It was found that the CEDIA method showed a Deming regression line of CEDIA=1.20xHPLC-MS/MS-0.07 (r=0.934, SEE=.47), with a mean bias of 20.4%. Serial blood samples from 8 patients included in this evaluation showed that the CEDIA method reflected the clinical fluctuations in the chromatographic methods, albeit with the variable bias noted. The CEDIA method on the H917 analyzer is therefore a useful adjunct to SRL dosage individualization in renal transplant recipients.

BOOP is common in cardiac transplant recipients switched from a calcineurin inhibitor to sirolimus

While bronchiolitis obliterans organizing pneumonia (BOOP) has been associated with the use of sirolimus (SIR), the incidence in a consecutive group of patients given SIR to replace a calcineurin-inhibitor (CI) is unknown. Twenty-nine consecutive cardiac transplant recipients were switched from a CI to SIR to ameliorate CI-associated nephropathy or coronary graft atherosclerosis. Seven patients (24%) developed BOOP. The clinical characteristics and biopsy results of these patients are presented. The clinical course and response to withdrawal of SIR in all and steroids in four of seven patients suggested the diagnosis of BOOP. Chest X-rays and CT scans showed typical findings of BOOP in all seven patients. Infection was excluded in all patients. Biopsy results were characteristic of BOOP in six of seven patients. Six patients recovered and one died. BOOP is a common and potentially serious adverse event in cardiac transplant patients switched from a CI to SIR, especially when SIR is started late post-transplantation.

Sirolimus: a new option in transplantation

This review of immunosuppression in renal transplantation has allowed us to highlight the deleterious effect of calcineurin inhibitor nephrotoxicity and to emphasise the importance of sirolimus. Now, a whole new set of possibilities has opened up in immunosuppression: sirolimus-based immunosuppression without calcineurin inhibitors; sirolimus in combination with calcineurin inhibitors in reduced doses; early calcineurin inhibitor withdrawal from a regimen that combines sirolimus, calcineurin inhibitors and steroids; and calcineurin inhibitor conversion to sirolimus when the first signs of graft nephrotoxicity appear. These new strategies in immunosuppression in renal transplantation are associated with good results in graft and patient survival in year 1, and with better renal function. Therefore, we can hope for better long-term results in transplantation, with a significant increase in the graft half-life and in the patient survival.

Consequences of genetic polymorphisms for sirolimus requirements after renal transplant in patients on primary sirolimus therapy

Sirolimus (SRL) is a substrate for cytochromes P-450 3A and P-glycoprotein, the product of the MDR1 gene. We postulated that single nucleotide polymorphisms (SNPs) of these genes could be associated with inter-individual variations in SRL requirements. We then evaluated in 149 renal transplant recipients the effect of polymorphisms CYP3A4*1/*1B, CYP3A5*1/*3 and MDR1 SNPs in exon 12, 21 and 26 on SRL concentration/dose (C/D) ratio 3 months after sirolimus introduction. SRL C/D ratio was significantly higher in patients treated with calcineurin inhibitors. The CYP3A4*1B and CYP3A5*1 alleles were present in 17% and 21% of patients, respectively. When treated with a SRL-based therapy and low-dose steroids, patients carrying the CYP3A4*1B or the CYP3A5*1 alleles required significantly more SRL to achieve adequate blood trough concentrations (p < 0.01 and p < 0.02, respectively). None of the MDR1 SNPs was associated with the SRL concentration/dose ratio. These findings suggest that the variations in SRL requirements are secondary to both genetic and non-genetic factors including pharmacokinetic interactions. In patients with SRL-based therapy, genotyping of the CYP3As genes may help to optimize the SRL management in transplant recipients.

High-performance liquid chromatography with ultraviolet detection for therapeutic drug monitoring of everolimus

We developed and validated a high-performance liquid chromatography-ultraviolet (HPLC-UV) method for determining everolimus concentrations in human whole blood. Sample preparation involved a solid-phase extraction after protein precipitation. The separation of everolimus from internal standard (IS) and endogenous components was achieved using an isocratic elution on an octyl column. The method showed a linear relationship between peak height ratios and blood concentrations in the range of 1-200 ng/mL (r(2)=0.9997). The observed intra- and inter-day assay imprecision had a coefficient of variation (CV)=12.8%, and inaccuracy was 11.4%. The method was found to be precise, accurate, and sensible making it useful for routine therapeutic monitoring of everolimus.

Immunosuppressive drug monitoring - what to use in clinical practice today to improve renal graft outcome

Therapeutic drug monitoring (TDM) of immunosuppressive therapy is becoming an increasingly complex matter as the number of compounds and their respective combinations are continuously expanding. Unfortunately, in clinical practice, monitoring predose trough blood concentrations is often not sufficient for guiding optimal long-term dosing of these drugs. The excellent short-term results obtained nowadays in renal transplantation confer a misleading feeling of safety despite the fact that long-term results have not substantially improved, definitely not to a point where longer graft survival could counteract the increasing need for transplant organs and less toxicity and side-effects could ameliorate patient survival. It is therefore a challenging task to try to tailor immunosuppressive drug therapy to the individual patient profile and this in a time-dependent manner. For the majority of currently used immunosuppressive drugs, measurement of total drug exposure by determination of the dose-interval area under the concentration curve (AUC) seems to provide more useful information for clinicians in terms of concentration-exposure and exposure-response as well as reproducibility. To simplify this laborious way of measuring drug exposure, several validated abbreviated AUC profiles, accurately predicting the dose-interval AUC, have been put forward. Together with an increasing knowledge of the time-related pharmacokinetic behaviour of immunosuppressive drug and their metabolites, studies are focusing on how to apply abbreviated AUC sampling methods in clinical transplantation, taking into account the numerous factors affecting drug pharmacokinetics. Eventually, TDM using abbreviated AUC profiles has to be prospectively tested against classic methods of drug monitoring in terms of cost-effectiveness, feasibility and clinical relevance with the ultimate goal of improving patient and graft survival.

A multicenter pilot study of early (4-day) steroid cessation in renal transplant recipients under simulect, tacrolimus and sirolimus

This study presents the first prospective multicenter study assessing sirolimus-based immunosuppression with early (4-day) corticosteroid withdrawal (CSWD) in renal transplantation. Immunosuppression included: anti-IL-2 receptor antibody and tacrolimus/sirolimus. Inclusion criteria included adult primary recipients. Exclusion criteria included: (i) African Americans, (ii) current PRA >50%, (iii) multiple organ transplants, (iv) WBC < 3000 cells/microL and (v) fasting hypercholesterolemia/hypertriglyceridemia. The primary endpoints were acute rejection and the proportion of patients off corticosteroids. Seventy-seven patients were enrolled: mean age of 49.7 +/- 12 years. Transplants included: cadaveric (26%) and living donor (74%). Patient and graft survival were 100%. Biopsy proven acute rejection occurred in 13%; presumptive rejection in 10.5%. Banff grades included: IA (seven patients), IB (one patient), IIA (one patient) and IIB (one patient). Renal function at 1 year: serum creatinine (1.18 +/- 0.06 mg/dL). Mean weight gain was minimal at 1 year: 3 +/- 2 kg/patient. Mild increases in total, LDL and HDL cholesterol were observed and new antilipid agent use occurred in 26 patients. In conclusion, early CSWD under tacrolimus/sirolimus-based immunosuppression in selected, low-risk renal transplant recipients provides: (i) excellent patient and graft survival, (ii) good renal function, (iii) reduced hyperlipidemia and antilipid agent use and (iv) low acute rejection rates.

Benefit-Risk Assessment of Sirolimus in Renal Transplantation

Sirolimus (rapamycin) is a macrocyclic lactone isolated from a strain of Streptomyces hygroscopicus that inhibits the mammalian target of rapamycin (mTOR)-mediated signal-transduction pathways, resulting in the arrest of cell cycle of various cell types, including T- and B-lymphocytes. Sirolimus has been demonstrated to prolong graft survival in various animal models of transplantation, ranging from rodents to primates for both heterotopic, as well as orthotopic organ grafting, bone marrow transplantation and islet cell grafting. In human clinical renal transplantation, sirolimus in combination with ciclosporin (cyclosporine) efficiently reduces the incidence of acute allograft rejection. Because of the synergistic effect of sirolimus on ciclosporin-induced nephrotoxicity, a prolonged combination of the two drugs inevitably leads to progressive irreversible renal allograft damage. Early elimination of calcineurin inhibitor therapy or complete avoidance of the latter by using sirolimus therapy is the optimal strategy for this drug. Prospective randomised phase II and III clinical studies have confirmed this approach, at least for recipients with a low to moderate immunological risk. For patients with a high immunological risk or recipients exposed to delayed graft function, sirolimus might not constitute the best therapeutic choice--despite its ability to enable calcineurin inhibitor sparing in the latter situation--because of its anti-proliferative effects on recovering renal tubular cells. Whether lower doses of sirolimus or a combination with a reduced dose of tacrolimus would be advantageous in these high risk situations remains to be determined. Clinically relevant adverse effects of sirolimus that require a specific therapeutic response or can potentially influence short- and long-term patient morbidity and mortality as well as graft survival include hypercholesterolaemia, hypertriglyceridaemia, infectious and non-infectious pneumonia, anaemia, lymphocele formation and impaired wound healing. These drug-related adverse effects are important determinants in the choice of a tailor-made immunosuppressive drug regimen that complies with the individual patient risk profile. Equally important in the latter decision is the lack of severe intrinsic nephrotoxicity associated with sirolimus and its advantageous effects on arterial hypertension, post-transplantation diabetes mellitus and esthetic changes induced by calcineurin inhibitors. Mild and transient thrombocytopenia, leukopenia, gastrointestinal adverse effects and mucosal ulcerations are all minor complications of sirolimus therapy that have less impact on the decision for choosing this drug as the basis for tailor-made immunosuppressive therapy. It is clear that sirolimus has gained a proper place in the present-day immunosuppressive armament used in renal transplantation and will contribute to the development of a tailor-made immunosuppressive therapy aimed at fulfilling the requirements outlined by the individual patient profile.

Determination of rapamycin: quantification of the sodiated species by an ion trap mass spectrometer as an alternative to the ammoniated complex analysis by triple quadrupole

Rapamycin is a potent immunosuppressive drug capable of significantly reducing acute graft rejection in kidney, liver and heart transplant patients. Its immunosuppressive activity and adverse effects have been related to rapamycin concentration, and therapeutic drug monitoring of the drug is deemed appropriate. This work was aimed at developing a new quantification method based on the isolation of the [M+Na]+ ion as precursor and its further fragmentation through an ion trap mass spectrometer equipped with an electrospray ionization source. A limit of detection (LOD) of 0.7 ng/mL was obtained, while the lower limit of quantification (LLOQ) was 2.4 ng/mL. The accuracy and reproducibility of the responses were evaluated and compared with results obtained when the [M+NH4]+ ion was chosen as the precursor in a triple quadrupole mass spectrometer. In this case the LOD was 0.5 ng/mL and the LLOQ 1.7 ng/mL. Data showed that it would be possible to use the quantification of the sodiated species for the routine determination of rapamycin, as an alternative to the commonly adopted method based on the ammoniated complex.

Immunosuppressive drug monitoring of sirolimus and cyclosporine in pediatric patients

Sirolimus is primarily used as a rescue agent in pediatric transplant recipients, particularly in cases of cyclosporine or tacrolimus toxicity. Preliminary data indicate a higher apparent oral clearance in younger children (4-10 years of age). Various drug interactions have been described between sirolimus and drugs that are substrates/inhibitors or inducers of CYP3A and the P-glycoprotein transporter. Close monitoring of trough sirolimus blood levels is therefore recommended for pediatric transplant recipients. In de novo adult kidney transplant recipients on triple therapy with cyclosporine, corticosteroids and sirolimus, a therapeutic window of 4-12 microg/l is recommended for sirolimus trough concentrations determined by HPLC or LC/MS-MS. In maintenance adult patients after conversion to a calcineurin inhibitor-free regimen, sirolimus trough concentrations of 5-10 microg/l are proposed in combination with mycophenolate mofetil. These therapeutic ranges may also serve as a guide for pediatric renal transplant recipients. The concept of C2 monitoring still needs to be critically evaluated in pediatric patients. The crucial importance of achieving an adequate cyclosporine exposure early after transplantation has been demonstrated for adult transplant recipients. A cyclosporine concentration taken 2 h after dosing is a good surrogate marker of the AUC0-4h in adults. Various clinical studies have shown that in pediatric patients, the C2 concentration shows a substantially better correlation with cyclosporine exposure compared to the trough level (C0). In an outcome study with pediatric renal transplant recipients, it could be demonstrated that the AUC(0-4h) was a predictor of acute rejection in the first 3 weeks after transplantation, whereas C2 levels showed no significant association. Abbreviated AUC strategies may be preferable for optimization of CsA exposure in pediatric patients.

Effect of immunosuppressive agents on long-term survival of renal transplant recipients: focus on the cardiovascular risk

In the control of acute rejection, attention is being focused more and more on the long-term adverse effects of the immunosuppressive agents used. Since cardiovascular disease is the main cause of death in renal transplant recipients, optimal control of cardiovascular risk factors is essential in the long-term management of these patients. Unfortunately, several commonly used immunosuppressive drugs interfere with the cardiovascular system. In this review, the cardiovascular adverse effects of the immunosuppressive agents currently used for maintenance immunosuppression are thoroughly discussed. Optimising immunosuppression means finding a balance between efficacy and safety. Corticosteroids induce endothelial dysfunction, hypertension, hyperlipidaemia and diabetes mellitus, and impair fibrinolysis. The use of corticosteroids in transplant recipients is undesirable, not only because of their cardiovascular effects, but also because they induce such adverse effects as osteoporosis, obesity, and atrophy of the skin and vessel wall. Calcineurin inhibitors are the most powerful agents for maintenance immunosuppression. The calcineurin inhibitor ciclosporin (cyclosporine) not only induces these same adverse effects as corticosteroids but is also nephrotoxic. Tacrolimus has a more favourable cardiovascular risk profile than ciclosporin and is also less nephrotoxic. It has little or no effect on blood pressure and serum lipids; however, its diabetogenic effect is more prominent in the period immediately following transplantation, although at maintenance dosages, the diabetogenic effect appears to be comparable to that of ciclosporin. The diabetogenic effect of tacrolimus can be managed by reducing the dose of tacrolimus and early corticosteroid withdrawal. The effect of tacrolimus on endothelial function has not been completely elucidated. The proliferation inhibitors azathioprine and mycophenolate mofetil (MMF) have little effect on the cardiovascular system. Yet, indirectly, by inducing anaemia, they may lead to left ventricular hypertrophy. MMF is an attractive alternative to azathioprine because of its higher potency and possibly lower risk of malignancies. Sirolimus also induces anaemia, but may be promising because of its antiproliferative features. Whether the hyperlipidaemia induced by sirolimus counteracts its beneficial effects is, as yet, unknown. It may be combined with MMF, however, initial attempts resulted in severe mouth ulcers.

Current and future immunosuppressive strategies in renal transplantation

The past decade has witnessed the introduction of several new immunosuppressive agents. The availability of these new pharmacologic offerings has not diminished the challenge of achieving a balance of adequate graft protection while minimizing the consequences of excessive immunosuppression. For renal transplant recipients, maintenance immunosuppression generally consists of a calcineurin inhibitor in combination with an antiproliferative agent and a corticosteroid; more recently, mammalian target of rapamycin inhibitors have been used. Excellent results have been achieved at many transplant centers with combinations of these agents in a variety of protocols. Regimens designed to limit or eliminate calcineurin inhibitor and/or corticosteroid therapy are actively being pursued in the transplant community. Allograft tolerance and xenotransplantation are being studied, and the knowledge gained from the effort may help in the development of innovative strategies and new immunosuppressive agents.

Pharmacogenetics and pharmacogenomics of immunosuppressive agents: perspective for individualized therapy

Immunosuppressive therapy has markedly improved over the past years with the advent of highly potent and rationally targeted immunosuppressive agents. Since these drugs are characterized by a narrow therapeutic index, major efforts have been carried out to define therapeutic windows based on the blood levels of each immunosuppressant, and relating those concentrations to clinical events. Although pharmacokinetic-based approaches are currently used as useful tools to guide drug dosing, they present several limitations. Pharmacogenomics – a science that studies the inherited basis of differences between individual responses to drugs in order to identify the best dose and therapy for each patient – might represent a complementary support. Preliminary studies that have focused on polymorphisms of genes encoding enzymes involved in drug metabolism, drug distribution, and pharmacological target, have shown promising results. Indeed, pharmacogenomics holds promise for improvement in the ability to individualize pharmacological therapy based on the patient’s genetic profile.

Prospects for personalized immunosuppression: pharmacologic tools--a review

In the last few years, novel immunosuppressive agents and new formulations, including sirolimus, mycophenolic acid (the active metabolite of mycophenolate mofetil), tacrolimus, and microemulsion cyclosporine, have significantly improved the clinical outcome of transplant recipients. However, the majority of immunosuppressive agents need a constant monitoring of drug levels to reduce the risk of graft rejection as well as drug-induced toxicities. Many factors may affect the pharmacokinetic characteristics of immunosuppressive agents, potentially reducing treatment effectiveness. Absorption and metabolism of immunosuppressive drugs are influenced by patient genotype and comedications, while comorbidities (ie, diabetes and cystic fibrosis) are responsible for altered pharmacokinetics. Dose individualization in transplant recipients is performed according to their health status, graft function, and drug therapeutic range. With respect to the last issue, therapeutic drug monitoring (TDM) plays a crucial role in achieving optimal immunosuppression, improving the efficacy of drugs, and lowering toxic effects. Pharmacokinetic analysis allowed the identification of specific parameters, such as plasma or blood levels, immediately before dosing (C(min) or trough levels) or 2 hours after administration (C(2)), which are significantly related to tissue exposure to the drug. More recently, studies have investigated treatment individualization by evaluating drug pharmacogenetics based on the expression level or mutations of their molecular targets, including calcineurin for cyclosporine and tacrolimus, and inosine monophosphate dehydrogenase for mycophenolic acid. Although no conclusive data may be drawn from these preliminary trials, further studies are underway to address the role of pharmacogenetics in clinical decision making.

Preservation of graft function in low-risk living kidney transplant recipients treated with a combination of sirolimus and cyclosporine

The use of sirolimus (SRL) in combination with full doses of cyclosporin A (CsA) results in reduced one-year kidney allograft function, which is associated with shorter long-term allograft survival. We determined the effect of reduced CsA exposure on graft function in patients receiving SRL and prednisone. Ninety recipients of living kidney transplants receiving SRL (2 mg/day, po) were compared to 35 recipients receiving azathioprine (AZA, 2 mg kg-1 day-1, po). All patients also received CsA (8-10 mg kg-1 day-1, po) and prednisone (0.5 mg kg-1 day-1). Efficacy end-point was a composite of biopsy-confirmed acute rejection, graft loss, or death at one year. Graft function was measured by creatinine, creatinine clearance, and graft function deterioration between 3 and 12 months (delta1/Cr). CsA concentrations in patients receiving SRL were 26% lower. No differences in one-year composite efficacy end-point were observed comparing SRL and AZA groups (18 vs 20%) or in the incidence of biopsy-proven acute rejection (14.4 and 14.3%). There were no differences in mean +/- SD creatinine (1.65 +/- 0.46 vs 1.60 +/- 0.43 mg/dl, P = 0.48) or calculated creatinine clearances (61 +/- 15 vs 62 +/- 13 ml/min, P = 0.58) at one year. Mean +/- SD delta1/Cr (-11 +/- 17 vs -14 +/- 15%, P = 0.7) or the percentage of patients with >20% (26 vs 31%, P = 0.6) or >30% delta1/Cr (19 vs 17%, P = 1) did not differ between the two groups. The use of 2-mg fixed oral doses of SRL and reduced CsA exposure was effective in preventing acute rejection and preserving allograft function.

Tolerability and steady-state pharmacokinetics of everolimus in maintenance renal transplant patients

BACKGROUND

Current immunosuppressant regimens need to be improved to prevent acute and chronic graft rejection. The novel macrocyclic immunosuppressant everolimus (Certican, RAD) is currently in clinical development to address this issue.

METHODS

The primary objective of this multicentre, randomized, double-blind, placebo-controlled, dose-escalating phase 1 study was to evaluate the safety and tolerability of everolimus at four dose levels (0.75, 2.5, 5 and 10 mg/day) in maintenance renal transplant patients receiving cyclosporin and steroids. The secondary objective was to assess the pharmacokinetic profile of two different formulations (capsule and tablet) of everolimus.

RESULTS

Fifty-four subjects were randomized for 4 weeks treatment with everolimus (n = 44) or placebo (n = 10). Dose levels of everolimus between 0.75 and 5 mg daily were well tolerated, permitting dose escalation to the highest everolimus dose of 10 mg daily. At this dose, everolimus was associated with a higher incidence and severity of adverse events, most notably thrombocytopenia. Pharmacodynamic assessment showed a relationship between drug exposure and thrombocytopenia. Notable reversible elevations of cholesterol were also observed at the 10 mg/day dose. Other changes in laboratory evaluations, including triglycerides, were minor, reversible and did not appear to be dose dependent. The bioavailability of the tablet formulation was 2.6-fold higher compared with the capsule, with evidence for dose proportionality over the dose range tested. Within-subject pharmacokinetic variability was low (coefficient of variation: 10-19%); however, between-subject variability ranged from 34 to 60% for AUC and C(max).

CONCLUSIONS

These results indicate that up to 5 mg/day everolimus results in a dose-proportional exposure, and is adequately well tolerated in renal transplant recipients receiving cyclosporin and steroids.

Therapeutic drug monitoring of sirolimus: effect of concomitant immunosuppressive therapy and optimization of drug dosing

Sirolimus (SRL) is a new immunosuppressant which shares a common metabolic pathway with several other immunosuppressive agents. This leads to potential pharmacokinetic interactions that might affect SRL blood levels with relevant clinical consequences. As a validated laboratory, 2658 SRL trough samples (corresponding to 495 kidney transplant recipients treated with different immunosuppressive regimens) from more than 40 Italian Transplant Units were analyzed. We found that dose-normalized SRL trough levels were significantly higher in patients treated with cyclosporine (CsA) and SRL (4.15 +/- 2.23 ng/mL/mg SRL), compared with patients treated with mycophenolate mofetil (MMF) and SRL (3.26 +/- 1.86 ng/mL/mg SRL; p < 0.01) or with MMF, steroids and SRL (2.52 +/- 1.73 ng/mL/mg SRL; p < 0.01). Mean intra- and interpatient variabilities were 19% and 47%, respectively. Both parameters are significantly affected by the time postsurgery, with the first week post transplantation being associated with the greatest variability. As additional analysis, a simple dose-adjustment formula has been proposed as a useful tool to guide SRL dose changes. The proposed equation has been able to predict SRL concentration after a dose change in 73% of the tested samples. These findings suggest that different immunosuppressants significantly interfere with SRL bioavailability. Strategies aimed at reducing variability in SRL exposure may have a positive clinical impact.

Rapid simultaneous quantification of immunosuppressants in transplant patients by turbulent flow chromatography combined with tandem mass spectrometry

BACKGROUND

Immunosuppressant therapeutic drug monitoring (TDM) is an important requirement in the management of post-transplant patients. Our aim was to develop and evaluate a robust high-throughput method using turbulent flow chromatography (TFC) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous quantification of cyclosporin A (CsA), tacrolimus (FK 506) and sirolimus.

METHODS

A total of 1483 EDTA-blood pre-dosage samples from 147 kidney, 67 liver, 15 kidney/pancreas, and 48 bone marrow recipients were collected. After hemolysis and protein precipitation of 50 microl blood, fast and efficient on-line matrix elimination was achieved using turbulent flow chromatography. Tandem mass spectrometric detection and quantification was performed using multiple reaction monitoring (MRM).

RESULTS

The total analysis time of the column switching method was 3 min. The method was linear from 4.5 to 1500 ng/ml for cyclosporin A, from 0.2 to 100 ng/ml for tacrolimus, and from 0.4 to 100 ng/ml for sirolimus. The accuracy was >95%. Within and between-run assay variation coefficients ranged from 2.4% to 9.3%. Excellent correlation with other standard methods (immunoassay, HPLC) was observed.

CONCLUSIONS

The presented turbulent flow chromatography-tandem mass spectrometric platform offers a very fast, simple and economical method with an excellent validation profile and is well suited for daily pre- and post-dosage immunosuppressant monitoring.

Wound-healing complications after kidney transplantation: a prospective, randomized comparison of sirolimus and tacrolimus

BACKGROUND

Sirolimus has been associated with an increased risk of wound-healing complications in several retrospective analyses. The authors compared the rates of wound-healing complications in renal allograft recipients in a prospective, randomized trial of sirolimus-mycophenolate mofetil-prednisone versus tacrolimus-mycophenolate mofetil-prednisone.

METHODS

All patients received antithymocyte globulin induction. In the first phase of the study, patients (n = 77) were included regardless of body mass index (BMI). In the second phase (n = 46 patients), the authors excluded patients with a BMI greater than 32 kg/m2, and the target trough sirolimus level was lowered to 10 to 15 ng/mL (previously 15-20 ng/mL). Multivariate logistic regression analyses were performed to identify predictors of wound complications.

RESULTS

Fifty-nine patients received tacrolimus and 64 received sirolimus and were included in subsequent analyses. The incidence of complications was 8% (5 of 59) in the tacrolimus group and 47% (30 of 64) in the sirolimus group (P < 0.0001). Rates of perigraft fluid collections, superficial wound infections, and incisional herniae were significantly higher in the sirolimus group. Multivariate logistic regression showed only sirolimus (P = 0.0001) and BMI (P = 0.0021) to independently correlate with complications. In the first phase of the study, the wound complication rate in the sirolimus group was 55% (21 of 38 patients). After excluding obese recipients and decreasing the target sirolimus level, the wound complication rate in the sirolimus group was 35% (9 of 26 patients; P = 0.1040).

CONCLUSIONS

The use of sirolimus-based immunosuppressive regimens leads to a higher incidence of wound-healing complications and will require new approaches to patient selection and management to decrease their incidence.

Synergistic effects of sirolimus with cyclosporine and tacrolimus: analysis of immunosuppression on lymphocyte proliferation and activation in rat whole blood

BACKGROUND

Whole-blood analysis of lymphocyte function was used to investigate the pharmacodynamic (PD) interaction of sirolimus (SRL) with cyclosporine (CsA) or tacrolimus (TRL) in vitro and to determine the relation between PD and pharmacokinetics (PK) of SRL in an in vivo rat model.

METHODS

In vitro, experiments involved incubation of increasing concentrations (0.25-25 [corrected] nM) of SRL with either CsA or TRL in rat whole blood. For the in vivo study, rats were orally treated with different doses of SRL alone (1, 3, 5, or 8 mg/kg) or with a combination of 3 mg/kg SRL plus 2.5 or 5 mg/kg CsA. Blood was obtained before and at different times after dosing. Inhibition of lymphocyte proliferation (proliferating cell nuclear antigen [PCNA]) and activation (CD25, CD71, CD11a, CD134) in mitogen-stimulated blood was determined using fluorescence-activated cell sorter analysis. SRL and CsA blood concentrations were determined at the same time points by light chromatography tandem mass spectrometry (LC-MS).

RESULTS

In vitro, concentrations of SRL between 0.25-25 [corrected] nM acted synergistically in combination with CsA or TRL at concentrations between 0.25-1.0 [corrected] nM. Higher SRL concentrations did not further increase inhibition of lymphocyte function in these combinations. In vivo, good correlations (r=0.68-0.94) were observed between PD parameters of lymphocyte function and SRL-PK and dose. Increasing SRL doses produced higher blood concentrations, but SRL doses of 8 mg/kg did not further increase inhibition of lymphocyte function. PD effects on lymphocyte function were prolonged, but maximal inhibition was not increased when SRL was applied in combination with CsA as compared to SRL mono therapy.

CONCLUSIONS

The results suggest that analysis of lymphocyte function in whole blood may be useful to optimize dosing of SRL in combination with CsA or TRL and that PD monitoring of immunosuppressive drugs will enhance the value of PK monitoring.

Platelet-Independent defect in hemostasis associated with sirolimus use

Sirolimus is currently used to prevent rejection of solid organ transplant, and sirolimus-eluting stents have shown promise for the prevention of coronary artery restenosis. Thrombocytopenia is a well-known adverse effect of sirolimus limiting its use. Herein we report on a patient in whom sirolimus caused a platelet-independent hemostasis defect. The patient was a 52-year-old woman who underwent renal transplant with consequent normal kidney function. The immunosuppressive regimen included basiliximab, steroids, and cyclosporine induction later shifted to sirolimus and mycophenolate due to biopsy findings of tubular necrosis on day 6 posttransplantation. At discharge the serum creatinine was 0.7 mg/dL. Four months after transplantation the patient was admitted to our hospital because of fever (37.5 degrees C to 38 degrees C), anorexia, and asthenia. Blood analysis showed: creatinine 1.7 mg/dL, Hb 9.6 g/dL, WBC 6 x 10(3)/microL, PLT 123 x 10(3)/microL, liver function tests normal, LDH 720 mU/mL, fibrinogen 628 mg/dL, d-dimer 0.42 ng/mL, FDP > 40 ng/mL, INR 1.10, PT 87%, aPTT 40 seconds. Cultures and tests for infection were negative. Serum sirolimus level was 25.9 ng/mL. The following day the serum creatinine rose to 2.3 mg/dL and diuresis fell to 20 mL/h. Multiple bleeding times (Ivy test) performed before the renal biopsy were repeatedly over 30 minutes (normal 3 to 5 minutes), despite normal platelet count and platelet function studies. There was no spontaneous aggregation and in vitro aggregation was normal (collagen, ADP, adrenalin, and ristocetin induced). Coagulation studies showed a defect in fibrin formation and a reduction of fibrinolysis. Suspension of sirolimus treatment was followed by remission of fever, improvement of renal function (serum creatinine 1.2 mg/dL), and normalization of bleeding time.

From pharmacokinetics to pharmacogenomics: a new approach to tailor immunosuppressive therapy

One of the main tasks in the management of organ transplantation is the optimization of immunosuppressive therapy, in order to provide therapeutic efficacy limiting drug-related toxicity. In the past years major efforts have been carried out to define therapeutic windows based on blood/plasma levels of each immunosuppressant relating those concentrations to drug dosing and clinical events. Although this traditional approach is able to identify environmental and nongenetic factors that can influence drug exposure during the course of treatment, it presents limitations. Therefore, complementary strategies are advocated. The advent of the genomic era gives birth to pharmacogenomics, a science that studies how the genome as a whole, including single genes as well as gene-to-gene interactions, may affect the action of a drug. This science is of particular importance for drugs characterized by a narrow therapeutic index, such as the immunosuppressants. Preliminary studies focused on polymorphisms of genes encoding for enzymes actively involved in drug metabolism, drug transport and pharmacological target. Pharmacogenomics holds promise for improvement in the ability to individualize immunosuppressive therapy based on the patient's genetic profile, and can be viewed as a support to traditional therapeutic drug monitoring. However, the clinical applicability of this approach is still to be proven.

An open-label randomized trial of the safety and efficacy of sirolimus vs. azathioprine in living related renal allograft recipients receiving cyclosporine and prednisone combination

BACKGROUND

The ability of sirolimus (SRL), in combination with reduced exposure of cyclosporine, was investigated to prevent acute rejection and associated side effects.

METHODS

Between June 1999 and February 2000, 70 recipients of primary one-haplotype living-related donor renal allografts were randomized to receive SRL (2 mg/d) or azathioprine (AZA) (2 mg/kg/d) combined with cyclosporine and prednisone. The primary end-point was a composite of first occurrence of biopsy-confirmed acute rejection, graft loss, or death during the first 3 months after transplantation.

RESULTS

From week 4 to month 12, SRL patients received lower cyclosporine (week 4: 364 mg/d vs. 455 mg/d, p = 0.004; month 12: 195 mg/d vs. 255 mg/d, p = 0.038) doses and showed lower cyclosporine concentrations (week 4: 247 ng/mL vs. 309 ng/mL, p = 0.04; month 12: 143 ng/mL vs. 188 ng/mL, p = 0.045). Compared with AZA, SRL patients showed reduced 3-month primary end point (0% vs. 17.1%, p = 0.025), and reduced incidence of biopsy-confirmed acute rejection at 3 months (0% vs. 14.3%, p = 0.01) but not at 12 months (11.4% vs. 14.3%, NS). Mean creatinine at 12 months were not different (1.8 +/- 0.6 vs. 1.6 +/- 0.6, p = 0.23). Hyperlipidemia was the only adverse event more frequent among SRL patients (49% vs. 17%, p = 0.01). There were no differences in infections and no malignancies in both groups.

CONCLUSIONS

The combination of 2 mg fixed doses of SRL, reduced cyclosporine exposure and prednisone was associated with a low incidence of acute rejection and did not result in significantly impaired graft function compared with patients receiving AZA, standard doses of cyclosporine and prednisone.

Therapeutic monitoring of immunosuppressant drugs. Where are we?

The emergence of specific immunosuppressive drugs (cyclosporine, tacrolimus, mycophenolate mofetil and sirolimus) during the last two decades has contributed dramatically to the success of organ transplantation. However, optimum balance between therapeutic efficacy and the occurrence of side effects has been a real challenge for physicians, mainly due to inter- and intra-patient variability arising from pharmacokinetic, pharmacogenetic and pharmacodynamic individual properties. Therapeutic drug monitoring, defined as the measurement and interpretation of concentrations of these drugs in biological fluids, with as a final objective the prediction of organ responses, became an integral part of transplant protocols. New analytical techniques became available with different performances in terms of specificity and sensitivity. In addition, there has been progress in understanding the mechanisms of action of these drugs that have implications for the development of better monitoring strategies and for their coprescription. The purpose of this review is to examine the current strategies in use for the therapeutic drug monitoring of immunosuppressant drugs and to discuss some of the factors that impinge on the monitoring of these drugs.

Sirolimus: a ten-year perspective

Sirolimus, a macrocyclic lactone that displays a novel mechanism of immunosuppressive action, is a critical-dose drug requiring therapeutic drug monitoring for optimal outcomes. This immunosuppressive agent was studied in two multicenter, blinded clinical trials to reduce the incidence of acute rejection episodes when used in combination with cyclosporine and steroids versus azathioprine or placebo comparators. Cyclosporine withdrawal studies documented a long-term benefit of chronic sirolimus therapy on renal function, albeit with a modestly enhanced incidence of acute rejection episodes. I believe that minimal initial cyclosporine exposures de novo mitigate the need for eventual withdrawal for chronic nephropathy while preserving the immunosuppressive synergy during the maintenance phase. Recipients treated de novo with a sirolimus-cyclosporine combination tolerate steroid withdrawal at 1 month after living-donor or at 3 to 6 months after cadaveric kidney transplantation with only a 5% risk of acute rejection episodes and 6% incidence of chronic reactions within 3 years. However, sirolimus exacerbates the hypertriglyceridemic and hypercholesterolemic proclivities of transplant recipients and exerts myelosuppressive effects. Due to its apparent lack of nephrotoxicity, sirolimus has been employed for induction therapy in a calcineurin antagonist-free regimen in combination with either basiliximab or rabbit antilymphocyte sera for weak or strong immune responders, respectively, followed by introduction of a calcineurin antagonist upon resolution of the ischemia-reperfusion injury.

Testosterone concentrations and sirolimus in male renal transplant patients

Sirolimus damages the testes in animals; however, human data are sparse. We conducted a case-control study to obtain further insight into this issue and compared testosterone, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin concentrations in matched renal transplant patients who did or did not receive sirolimus. We found that testosterone values were lower (11.2 +/- 6.3 nmol/L vs. 15.5 +/- 7.7 nmol/L, p < 0.05), in 28 sirolimus-treated patients, compared to 28 non-sirolimus-treated controls. Furthermore, these patients more commonly had testosterone concentrations that were below our reference value for normal men. In contrast, FSH and LH concentrations were higher while prolactin levels were not different. These data are consistent with sirolimus-related testosterone suppression and suggest a need for further studies.

Determination of Sirolimus Blood Concentration Using High-Performance Liquid Chromatography with Ultraviolet Detection

BACKGROUND

Different HPLC methods have been developed and used to determined sirolimus blood concentrations. These methods show different performance characteristics, mostly related to peak interference, recovery, assay sensitivity, and turnaround times.

OBJECTIVE

We adapted, improved, and validated an HPLC method with UV detection for measurement of sirolimus in whole blood clinical samples.

METHODS

The standards, quality controls, or patient samples (0.25 or 0.5 mL) and internal standard (desmethoxysirolimus) were extracted with 1-chlorobutane. After evaporation, the extract was reconstituted in a 70% acetonitrile/water mixture and analyzed onto a reverse-phase C18 column at 50 degrees C under a flow rate of 1.0 mL/min in the HPLC system. Ultraviolet detection was performed at 278 nm, with sensitivity setting of 0.010 AUFS. Identification of peaks of interest was by retention time; quantification of sirolimus was based on a peak area ratio.

RESULTS

Analytic recovery ranging from 96 to 120% (CV = 3.7 to 16.8%; bias = -4.2 to 16.7%) was observed throughout the assay's linear range (2.5-150.0 ng/mL). The lower limit of quantification for both sample volumes (0.25 or 0.5 mL) was 2.5 ng/mL (CV = 12 and 15%, bias = -1.2 and 4%, respectively). The intra- and interassay imprecision ranged from 6.2 to 14.4% and from 9.1 to 18.6%, with bias ranging from 1.3 to 12.9% and -1.8% to 7.1, for quality control levels of 3, 10, and 20 ng/mL. Whole blood and extracted samples are stable at room temperature and at 4 and -20 degrees C for 1 week and 3 days, respectively. Chromatograms showed good separation free of interfering peaks. A set of 45 samples can be extracted in 2 h, allowing results within 24 h.

CONCLUSION

This HPLC-UV method shows good and reproducible performance, satisfying all requirements of an assay designated to be applied in therapeutic drug monitoring strategies after organ transplantation.

Dyslipidemia in renal transplant recipients treated with a sirolimus and cyclosporine-based immunosuppressive regimen: incidence, risk factors, progression, and prognosis

BACKGROUND

This retrospective study compared the incidence, severity, and predisposing factors for dyslipidemia among renal transplant patients treated for up to 6 years with a cyclosporine +/- prednisone-based concentration-controlled regimen without (n=118) or with (n=280) ascending exposures to sirolimus.

METHODS

The diagnosis of dyslipidemia was established when the serum cholesterol value (CHO) was more than 240 mg/dL or serum triglycerides (TG) were more than 200 mg/dL. Generalized estimating equations and mixed-modeling procedures were used for statistical analyses.

RESULTS

Hypercholesterolemia was observed in 46% to 80% and hypertriglyceridemia in 43% to 78% of sirolimus-treated patients during the first 6 posttransplantation months. The mean peak serum lipid levels among patients in the sirolimus group (CHO=285.5 mg/dL; TG=322.4 mg/dL) were significantly higher than those in the nonsirolimus group (CHO=250.2 mg/dL and TG=267.6 mg/dL; both P<0.01). The lipid values, which were persistently elevated during the first posttransplantation year, decreased slowly thereafter but remained significantly higher than the pretransplantation levels beyond 4 years after transplantation. The two forms of hyperlipidemia tended to occur in parallel (Pearson's coefficient of correlation, r=0.5, P<0.001), showing a positive predictive value of 0.67 and a negative predictive value of 0.65. However, there was no significant difference in the incidence of cardiovascular events within 4 years after transplantation among patients treated with versus without sirolimus.

CONCLUSION

The dyslipidemia associated with sirolimus therapy, albeit persistent, does not seem to represent a major risk factor for the early emergence of cardiovascular complications.

Safety and efficacy of sirolimus in kidney transplant patients and in patients with coronary artery disease undergoing angioplasty

We show the key results of our 4-year experience with sirolimus in kidney transplant patients and in nontransplanted patients undergoing coronary angioplasty.

METHODS

Recipients of one-haplotype living-related kidney allografts were randomized to receive sirolimus (2 mg/d, n = 35) or azathioprine (2 mg/kg per day, n = 35). Recipients of fully mismatched living kidney allografts (n = 55) received sirolimus (2 mg/day). High-risk recipients of black ethnicity (n = 68) were randomized to target whole-blood trough sirolimus concentrations between 8 and 12 ng/mL or 15 to 20 ng/mL. All kidney transplant patients received cyclosporine and prednisone. Sirolimus/cyclosporine pharmacokinetic studies were performed in 40 patients receiving 2 mg (n = 20) or 5 mg (n = 20) of sirolimus 7 days after transplantation. In the coronary intervention study, 12 patients at high risk for in-stent restenosis received sirolimus for 28 days after angioplasty.

RESULTS

The incidence of biopsy-confirmed acute rejection was 11.4% in recipients of one-haplotype living-related kidney allografts, 16.4% in recipients of fully mismatched living kidney allografts, and 15% (8 to 12 ng/mL) and 4% (15 to 20 ng/mL) in high-risk recipients of black ethnicity. Cyclosporine exposure was higher after morning administration compared to evening administration. There were poor correlations between sirolimus and cyclosporine exposures. The 4-month follow-up angiography revealed no restenosis (stenosis diameter > 50%), a late loss of 0.56 +/- 0.40 mm, and a loss index of 0.33 +/- 0.30. The follow-up 3D-intravascular ultrasound restudy showed an in-stent relative volumetric obstruction of 9.9 +/- 5.5%. Sirolimus in highly effective in preventing kidney allograft acute rejection and in-stent coronary restenosis.

Two-year results of multicenter phase III trials on the effect of the addition of sirolimus to cyclosporine-based immunosuppressive regimens in renal transplantation

Randomized clinical trials conducted over 24 months and including nearly 1300 renal transplant patients compared the efficacy and safety of two dose levels of sirolimus versus azathioprine (United States) or placebo (Global) comparators administered with a cyclosporine (CsA) and prednisone (Pred) baseline regimen. Analysis of 24-month data revealed that patients in the 5 mg/d sirolimus groups experienced a significant delay in the onset and reduction in the incidence of acute rejection episodes compared with azathioprine (Aza) or placebo groups (P =.02/P =.001). Graft and patient survival rates and also the occurrence of transplant-related infections, lymphoproliferative disorders, or malignancies were similar among all treatment arms. Between 12 and 24 months, patients treated with 2 mg/d sirolimus displayed relatively stable mean serum creatinine values, namely 1.9-1.8 mg/dL for the US and 1.8-1.8 mg/dL for the Global (P = NS) studies, which remained higher than those of the comparators. Both 5 mg/d groups showed an increase in mean serum creatinine during this interval, which was significantly higher than the value in both comparators at 24 months. Both sirolimus groups showed persistently elevated triglyceride levels compared with Aza-treated patients at month 24. The Global trial showed a less-pronounced difference in mean fasting triglyceride values compared with placebo. Data from both trials demonstrate that the addition of sirolimus to a CsA-Pred treatment regimen yielded a durable immunosuppressive effect associated with a progressive resolution of adverse side effects over time except for hyperlipidemia, which required continued countermeasure therapy.

Therapeutic monitoring of sirolimus: its contribution to optimal prescription

It is now common practice to measure immunosuppressive drugs in blood as a guide to therapy. The immunosuppressive drug sirolimus, recently approved for use following kidney transplantation, was developed in the context of this clinical approach. Throughout the early clinical studies, validated analytical techniques based on chromatographic techniques were used to measure the drug. After a brief period in which an immunoassay was available, routine measurements are again being performed by chromatographic assays. In this article the use of blood concentration measurements in the assessment of the early and pivotal clinical trials of the drug is documented. Then, the rationale for the routine monitoring of the drug in clinical practice, a regulatory requirement in some countries, is set out. It is concluded that the development of this compound has benefited from experience gained during the pharmacokinetic assessment of other immunosuppressive drugs. The pharmacokinetic data accumulated on sirolimus have been a key element in formulating guidelines on dosing with this drug, both when used in combination with cyclosporine and when used after cyclosporine withdrawal.

Ten years of sirolimus therapy in orthotopic liver transplant recipients

BACKGROUND

Sirolimus therapy has been used in orthotopic liver transplant (OLT) recipients diagnosed with a variety of diseases; chronic graft rejection (CR), calcineurin associated renal toxicity, preemptive immune suppression, calcineurin related neurotoxicity, preemptive therapy in transplant recipients with history of hepatocellular carcinoma, and steroid resistant allograft rejection.

METHODS

A search for the medical literature and experiences involving sirolimus was done.

RESULTS

Several animal and human reports evaluating the use sirolimus in liver transplant recipients are found and discussed.

CONCLUSION

Sirolimus has been used for multitude of indications, primarily based on anecdotal experiences. However, reports of sirolimus related side effects have decreased the transplant communities' enthusiasm towards promoting this agent as a safe immune suppression agent.

Sirolimus changes lipid concentrations and lipoprotein metabolism in kidney transplant recipients

BACKGROUND

Sirolimus (Rapammune, rapamycin, RAPA) is a strong immunosuppressive agent that reduces kidney transplant rejection. Hyperlipidemia is a significant side effect of sirolimus treatment and often leads to vascular disease. We have studied the repeatability, reversibility, and dose dependence of the plasma lipid and apoprotein changing effects of sirolimus and attempted to determine the mechanism by which sirolimus induces hypertriglyceridemia in some kidney transplant recipients.

METHODS

Six patients with renal allografts maintained on cyclosporine A and prednisone were selected on the basis of their previous hyperlipidemic response to short-term (14 days) sirolimus administration. For longer-term treatment, each patient was started on 10 mg/d sirolimus and continued as tolerated for 42 days to reinduce hyperlipidemia. Timed blood samples were analyzed for lipid, apoprotein, and sirolimus levels.

RESULTS

During sirolimus administration, mean total plasma cholesterol increased from 214 to 322 mg/dL (+50%); low density lipoprotein-cholesterol levels changed in a similar pattern. Mean triglyceride level rose from 227 to 432 mg/dL (+95%). ApoB-100 concentration rose from 124 to 160 mg/dL (+28%). ApoC-III level increased from 28.9 to 55.5 mg/dL (+92%). These lipid and apoprotein changes were found to be repeatable, reversible, and dose dependent. [(13)C(4)]-palmitate metabolic studies in four patients with hypertriglyceridemia indicated that the free fatty acid pool was expanded by sirolimus treatment (mean = 42.3%). Incorporation of [(13)C(4)]-palmitate into triglycerides of very low density lipoprotien, intermediate density lipoprotein, low density lipoproteins was decreased 38.3%, 42.1%, and 38.4%, respectively, by sirolimus treatment of these patients.

CONCLUSIONS

These results suggest that sirolimus alters the insulin signaling pathway so as to increase adipose tissue lipase activity, decrease lipoprotein lipase activity, or both, resulting in increased hepatic synthesis of triglyceride, increased secretion of VLDL, and increased hypertriglyceridemia.

Effects of sirolimus on plasma lipids, lipoprotein levels, and fatty acid metabolism in renal transplant patients

Sirolimus (Rapammune, rapamycin, RAPA) is a potent immunosuppressive drug that reduces renal transplant rejection. Hyperlipidemia is a significant side effect of sirolimus treatment, and frequently leads to cardiovascular disease. This study was undertaken to determine the repeatability, reversibility, and dose dependence of the plasma lipid and apolipoprotein altering effects of sirolimus, and to elucidate the mechanism by which sirolimus induces hypertriglyceridemia in some renal transplant patients. Six patients with renal allografts maintained on cyclosporine A and prednisone were selected on the basis of their previous hyperlipidemic response to short term (14 days) sirolimus administration. For longer-term treatment, each patient was started on 10 mg/day sirolimus and continued as tolerated for 42 days to reinduce hyperlipidemia. Timed blood samples were analyzed for lipid, apolipoprotein, and sirolimus levels. During sirolimus administration, mean total plasma cholesterol increased from 214 mg/dl to 322 mg/dl (+50%; range 25-92%); LDL-cholesterol levels followed a similar pattern. Mean triglyceride level rose from 227 to 432 mg/dl (+95%; range 9-254%). ApoB-100 concentration rose from 124 to 160 mg/dl (+28%; P < 0.05). ApoC-III level increased from 28.9 to 55.5 mg/dl, +92%; (P < 0.013). These lipid and apolipoprotein changes were found to be repeatable, reversible, and dose dependent. [(13)C(4)]palmitate metabolic studies in four patients with hypertriglyceridemia indicated that the free fatty acid pool was expanded by sirolimus treatment (mean = 42.3%). Incorporation of [(13)C(4)]palmitate into triglycerides of VLDL, IDL, and LDL was decreased 38.3%, 42,1%, and 38.4%, respectively, by sirolimus treatment of these patients. These results suggest that sirolimus alters the insulin signaling pathway so as to increase adipose tissue lipase activity and/or decrease lipoprotein lipase activity, resulting in increased hepatic synthesis of triglyceride, increased secretion of VLDL, and increased hypertriglyceridemia.

Assessment of sirolimus concentrations in whole blood by high-performance liquid chromatography with ultraviolet detection

A novel, reversed-phase high-performance liquid chromatographic (HPLC) method is described for the analysis of sirolimus (SRL) in whole blood. The samples were purified by precipitating blood matrix with zinc sulfate, SRL was then extracted with acetone followed by solid-phase extraction. The method was linear over a range of 1-100 ng/ml and the lower limit of quantification was 2.5 ng/ml. The coefficient of variation (within day) was below 8.0% for the lowest SRL concentration. The day-to-day coefficient of variation was below 6.6%. The assay did not show interference peaks with immunosuppressive drugs commonly given to transplant patients. With the simplified extraction procedure described, 60 samples (including controls and calibration curve) can be quantified in a day. The sensitivity and rapidity of this analytical procedure makes it useful for routine therapeutic monitoring of SRL.