[Rapamycin: a new immunosuppressive agent capable of inhibiting chronic rejection?]

Chronic rejection represents the most common cause of transplanted graft loss in the long term. Rapamycin (sirolimus), and it's derivate RAD, are new and potent, immunosuppressive drugs. They inhibit cell proliferation driven by various growth factors. These drugs were successfully tested in some experimental models of the chronic rejection. Results of the first clinical trials have defined rapamycin pharmacokinetics and proved immunosuppressive efficacy. Rapamycin acts synergistically with cyclosporin A. The side effects are a dose-dependent thrombocytopenia and leukopenia but the most frequent is hyperlipidemia. The question, if rapamycin and RAD inhibit development of chronic rejection in man, will be solved by the prospective clinical trials over years.

Pharmacokinetics and tolerability of 40-0-[2-hydroxyethyl]rapamycin in de novo liver transplant recipients

BACKGROUND

40-0-[2-Hydroxyethyl]rapamycin (RAD), a novel macrolide with potent immunosuppressive and antiproliferative activities, prevents rejection in animal allotransplantation models. This phase I trial assessed the effects of bile diversion, administration route, and time after transplant on RAD pharmacokinetics after single-dose administration in de novo liver allograft recipients. The influence of RAD on cyclosporine (CsA) pharmacokinetics and the safety of RAD were also evaluated.

METHODS

Twenty-six de novo liver allograft recipients were assigned to one of four treatment groups based on the presence or absence of a T tube, administration route (nasogastric or nasoduodenal), and timing of RAD administration. Patients received a single 7.5-mg RAD dose on one to three occasions in addition to CsA (Neoral) and corticosteroids. Steady-state cyclosporine profiles with and without RAD coadministration were evaluated. Results. Recipients with bile diversion demonstrated lower peak concentration (Cmax) than those without, but overall drug exposure (AUC) was not altered. Cmax and AUC were not influenced by administration route. A trend towards higher Cmax on postoperative day 3 than on postoperative day 1 was noted, although AUC was not altered. Single-dose RAD coadministration did not affect steady-state CsA pharmacokinetics. RAD was well tolerated and caused few drug-related adverse effects. RAD administration did not increase infection rates or produce clinically significant changes in laboratory parameters. Conclusions. In de novo liver transplant recipients, the overall extent of RAD absorption was not influenced by bile diversion, administration route, or time of administration. CsA pharmacokinetics were not affected by single-dose RAD coadministration. RAD capsules administered in single doses of 7.5 mg were well tolerated and safe.

Longitudinal assessment of everolimus in de novo renal transplant recipients over the first post-transplant year: pharmacokinetics, exposure-response relationships, and influence on cyclosporine

OBJECTIVE

Our objective was to characterize the steady-state pharmacokinetics of everolimus and cyclosporine (INN, ciclosporin) when coadministered in de novo kidney allograft recipients during the first year after transplantation.

METHOD

This study was a multicenter randomized double-blind study of 101 patients who were randomly assigned 1:1:1 to receive everolimus tablets at doses of 0.5 mg, 1 mg, or 2 mg twice daily with cyclosporine and prednisone. Blood sampling for the pharmacokinetics of everolimus and cyclosporine was performed on day 1, on weeks 1, 2, 3, and 4, and on months 2, 3, 6, 9, and 12. Everolimus dose-proportionality and stability over time were assessed in the context of linear regression and ANOVA models. Everolimus exposure-response relationships between area under the blood concentration-time curve (AUC) and changes in platelets, leukocytes, and lipids were explored with the median-effect model. Potential differences in cyclosporine dosing and pharmacokinetics at different levels of everolimus exposure were assessed in the context of ANOVA.

RESULTS

Everolimus steady state was reached on or before day 7, with a median 3-fold accumulation of drug exposure compared with that after the first postoperative dose. Both steady-state maximum concentration and AUC were dose proportional over the full dose range when assessed on day 1, as well as for the full duration of the study at steady state. There was evidence for longitudinal stability in AUC of everolimus during the course of the study. The interindividual pharmacokinetic variability for AUC was 85.4% and intraindividual, interoccasion variability was 40.8%. Age (range, 17-69 years), weight (range, 49-106 kg), and sex (65 men and 36 women) were not significant contributors to variability. There was an increasing incidence of transient thrombocytopenia (< or =100 x 10(9)/L) with increasing everolimus AUC (P = .03). Cyclosporine doses, trough concentrations, and AUC exhibited similar temporal patterns during the course of the study regardless of the co-administered everolimus dose level (P = .13, .82, and .76, respectively).

CONCLUSIONS

Everolimus exhibited dose-proportional, stable exposure during the first post-transplant year. For a 4-fold range of everolimus doses there were no differential effects on cyclosporine dosing or pharmacokinetics.

Pharmacokinetic interaction between single oral doses of diltiazem and sirolimus in healthy volunteers

AIM AND BACKGROUND

The pharmacokinetic interaction between sirolimus, a macrolide immunosuppressant metabolized by CYP3A4, and the calcium channel blocker diltiazem was studied in 18 healthy subjects. Several clinically important interactions have previously been reported for other immunosuppressive drugs that are metabolized by the same enzyme and for calcium antagonists.

METHODS

Healthy subjects who were 20 to 43 years old participated in an open, three-period, randomized, crossover study of the pharmacokinetics of a single 10-mg oral dose of sirolimus, a single oral 120-mg dose of diltiazem, and the two drugs given together. The three study periods were separated by a 21-day washout phase.

RESULTS

The geometric mean (90% confidence interval) whole blood sirolimus area under the plasma concentration time-curve increased 60% (35%-90%), from 736 to 1178 ng x h/mL, and maximum concentration increased 43% (14%-81%), from 67 to 96 ng/mL, with diltiazem coadministration, whereas the mean elimination half-life of sirolimus decreased slightly, from 79 to 67 hours. Apparent oral clearance and volume of distribution of sirolimus decreased with 38% and 45%, respectively, when sirolimus was given with diltiazem. The plasma maximum concentration and area under the plasma concentration-time curve of diltiazem, desacetyldiltiazem, and desmethyldiltiazem were unchanged after coadministration of sirolimus, and no potentiation of the effects of diltiazem on diastolic or systolic blood pressure or on the electrocardiographic parameters was seen.

CONCLUSIONS

Single-dose diltiazem coadministration leads to higher sirolimus exposure, presumably by inhibition of the first-pass metabolism of sirolimus. Because of the pronounced intersubject variability in the extent of the sirolimus-diltiazem interaction, whole blood sirolimus concentrations should be monitored closely in patients treated with the two drugs.

Immunosuppressant use without bone loss--implications for bone loss after transplantation

Cyclosporine A (CsA) is associated with posttransplantation bone disease. Immunosuppressant drugs such as sirolimus (SRL), which are more potent and less deleterious than CsA, are being developed. Previous experiments have shown that SRL although immunosuppressive, is relatively bone sparing. The use of low doses of CsA and SRL in combination has displayed in vivo synergism. This study was initiated to examine the effect of low-dose CsA and SRL on bone metabolism, thereby hopefully providing a bone sparing immunosuppressive regimen for transplant recipients. One hundred and nineteen rats were divided into groups: basal, vehicle, CsA high dose, CsA low dose, SRL low dose, and combination low-dose CsA and SRL. The basal group was killed on day 0 for histomorphometry. The experimental groups were weighed and bled on days 0, 28, 56, and 84 and were killed on day 84 for histomorphometry. Serial assays for blood urea nitrogen (BUN), creatinine, and osteocalcin were performed. Osteocalcin was raised on days 28 and 56 in the high dose CsA group. Histomorphometry showed osteopenia with high-dose CsA. Low-dose CsA was relatively bone sparing, while low-dose SRL and combined low-dose CsA did not cause bone loss. In conclusion, the synergistic combination of low-dose CsA and SRL has the potential of providing both bone sparing and immunosuppressive benefits.

Sirolimus: mammalian target of rapamycin inhibitor to prevent kidney rejection

Current immunosuppressive therapies are effective but can be associated with significant adverse reactions. Sirolimus works differently from the immunosuppressants currently available, and except for increased lipid levels, the adverse reaction profile of sirolimus does not appear to overlap to any great extent with that associated with cyclosporine or tacrolimus. While additional research is needed, the initial clinical data in kidney recipients suggest that sirolimus, in combination with cyclosporine or tacrolimus, might have the potential to reduce the frequency of rejection episodes, permit reductions in cyclosporine or tacrolimus dosage, and permit steroid withdrawal (Kelly, 1999).

Pharmacokinetics and safety of single oral doses of sirolimus (rapamycin) in healthy male volunteers

A phase I study was conducted to determine the pharmacokinetics, safety, and tolerability of sirolimus, a new immunosuppressive drug, in 45 healthy men between 19 and 36 years of age. Nine subjects in each group were randomly assigned to receive single oral doses of either sirolimus (n = 6) or placebo (n = 3) in group I (0.3 mg/m2), group II (1 mg/m2), group III (3 mg/m2), group IV (5 mg/m2) and group V (8 mg/m2). No serious adverse events occurred during the study. Twenty-eight of the 45 volunteers (62%) reported an adverse event; 19 of 30 (63%) were in the sirolimus group and 9 of 15 (60%) were in the placebo group (ns). Asthenia was the most common adverse event, occurring in 7 of 30 (23%) in the sirolimus group compared with 6 of 15 (40%) in the placebo group (ns). Absorption occurred within 1 hour in all volunteers. Whole blood peak concentration and area under the concentration-time curve increased proportionally with dose. Mean (+/- SD) whole blood terminal disposition half-life (t1/2), apparent oral dose clearance (Cl/F), and volume of distribution (Vss/F) were 82 +/- 12 hours, 278 +/- 117 mL/h x kg and 23 +/- 10 L/kg, respectively. Distribution of sirolimus into formed blood elements was extensive, with a mean whole blood-to-plasma ratio of 36. Single oral doses of sirolimus (0.3 to 8 mg/m2) solution were well tolerated in healthy male volunteers.

[Immunosuppressive macrolides and their use in dermatology]

The immunosuppressive macrolides are a novel class of antiinflammatory substances, which could supplant glucocorticosteroids for the topical treatment of some chronic inflammatory skin diseases. Cyclosporine A (CyA), well known from transplantation medicine for years, is licensed in Germany for oral treatment of psoriasis and atopic dermatitis but is not suitable for topical therapy. Tacrolimus (FK506) penetrates the inflamed epidermis and is regarded as the key immunosuppressive macrolide. Clinical trials have demonstrated the efficacy of FK506 ointment for atopic dermatitis, many case reports have been published regarding other inflammatory skin diseases. The ascomycin derivative ASM 981 has many of the properties of FK506 but less data is available at present. Sirolimus (Rapamycin) is structurally related to FK506 but has other biological effects since its molecular actions involve different biochemical pathways. A review of the biochemical and cellular properties, mode of action, therapeutic efficacy and unwanted side effects, as well as data from clinical trials and status of licensing, is given for the respective drugs.

Sirolimus: continuing the evolution of transplant immunosuppression

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and economic issues associated with sirolimus, the most recent immunosuppressive agent approved for kidney transplantation.

DATA SOURCES

A MEDLINE search (1966-June 2000) was completed to identify primary and review articles. In addition, abstracts from recent meetings on transplantation were reviewed for information and research on sirolimus.

STUDY SELECTION AND DATA EXTRACTION

Blinded, randomized, controlled studies were the goal, but, as with most newly approved immunosuppressive agents, a significant amount of information on sirolimus is not available in this optimal form. All articles were assessed and all pertinent information was incorporated in this review.

DATA SYNTHESIS

Sirolimus is structurally related to the immunosuppressive agent tacrolimus, and retains a pharmacokinetic and drug interaction profile similar to that of the calcineurin inhibitors, cyclosporine and tacrolimus. However, the novel mechanism of action of sirolimus differs significantly from these agents, as does its adverse effect profile. The most significant adverse reaction is hyperlipidemia. Clinical experience with sirolimus has allowed transplant centers to expand its use into other areas of transplantation as well as certain autoimmune disorders.

CONCLUSIONS

The definitive role of sirolimus will continue to be determined; however, sirolimus offers an excellent addition to the transplant immunosuppression armamentarium.

Requirements for therapeutic drug monitoring of sirolimus, an immunosuppressive agent used in renal transplantation

BACKGROUND

On September 15, 1999, sirolimus received approval from the US Food and Drug Administration (FDA) for marketing as an immunosuppressive agent. As with any chronically administered medication, the question arises whether therapeutic drug monitoring (TDM) is required for optimal therapy. In the case of sirolimus, there are data to suggest that TDM may be beneficial in some patients.

OBJECTIVE

To assess the need for monitoring sirolimus concentrations, this paper reviews the following factors influencing the usefulness of TDM: wide pharmacokinetic variability; toxicity; suspected noncompliance; suspected drug interactions; and specific demographic characteristics. Data supporting the correlation between sirolimus concentration and immunosuppressive efficacy are also discussed.

RESULTS

The available literature on sirolimus suggests that TDM may be required in some cases. Studies have shown that there is wide interindividual variability in the pharmacokinetic behavior of drugs in transplant patients; that there is a relationship between blood concentrations of sirolimus and adverse events; and that coadministration of cyclosporine alters the pharmacokinetics of sirolimus. Additionally, the correlation between sirolimus concentration and immunosuppressive efficacy in phase III trials suggests a benefit in transplant patients when sirolimus concentrations reach appropriate levels. Finally, noncompliance is a common occurrence in the transplant population, and monitoring is often necessary in suspected noncompliers.

CONCLUSION

Although additional clinical studies are needed, it appears that TDM is an important aspect of treatment with sirolimus.

Toxicity and efficacy of sirolimus: relationship to whole-blood concentrations

BACKGROUND

Sirolimus is a novel macrolide immunosuppressive drug with a mechanism of action distinct from that of both cyclosporine and tacrolimus. Recent clinical studies have demonstrated a decrease in acute rejection episodes in renal transplant patients receiving sirolimus compared with controls. The major toxicities associated with sirolimus treatment are thrombocytopenia and hyperlipidemia. In addition, concern has been raised by the higher serum creatinine levels noted in patients receiving sirolimus and cyclosporine compared with controls receiving cyclosporine and azathioprine.

OBJECTIVE

The objective of the present review is to summarize the efficacy and toxicity data for sirolimus. Special consideration is given to evidence that links these effects to dose or whole-blood concentrations of sirolimus.

RESULTS

The literature indicates that trough concentrations of sirolimus >15 ng/mL appear to be associated with a greater risk of both thrombocytopenia and hyperlipidemia, whereas trough sirolimus concentrations <6 ng/mL have been associated with an increased incidence of acute rejection.

CONCLUSION

The evidence to date supports target trough sirolimus concentrations of 6 to 15 ng/mL in most patients. In higher-risk groups and patients receiving cyclosporine-sparing regimens, higher concentrations may be necessary to achieve similar efficacy.

Pediatric utilization of rapamycin for severe cardiac allograft rejection

BACKGROUND

Rapamycin is a new immunosuppressive agent that has been shown to be effective in the treatment of acute cardiac rejection in the adult population.

METHODS

This case documents a pediatric patient with ongoing cardiac rejection that did not abate despite treatment with antithymocyte serum (RATS), corticosteroid pulses, and methotrexate in addition to daily prednisone, mycophenolate mofetil, and tacrolimus.

RESULTS

Initiation of therapy with rapamycin resulted in a rapid resolution of cardiac rejection and reduction of concomitant immunosuppressive agents and few side effects.

CONCLUSIONS

This case illustrated the utilization of rapamycin in a pediatric patient with ongoing acute rejection despite several modifications in treatment.

Sirolimus-induced thrombocytopenia and leukopenia in renal transplant recipients: risk factors, incidence, progression, and management

BACKGROUND

Our study assessed the factors that predispose renal transplant recipients to the occurrence of thrombocytopenia and leukopenia, as well as the severity and the time- and concentration-dependence of these side-effects, after administration of sirolimus (SRL) in combination with a cyclosporine (CsA) and prednisone (Pred) regimen.

METHODS

The clinical courses of two cohorts of renal transplant recipients were compared over 1 year: 119 patients received SRL in addition to CsA and Pred, and 65 demographically similar, concurrent patients received only CsA and Pred. Using an analysis of variance, pretransplant laboratory values and SRL trough concentrations (C0) were correlated with the occurrence, severity, and persistence of drug-induced thrombocytopenia (platelet count <150x10(3) cell/mm3) and/or leukopenia (white blood cell count <5,000/mm3).

RESULTS

Neither the ethnic background nor the pretransplant cytomegalovirus serological status was associated with the occurrence of hematological complications. Thrombocytopenia was usually observed during the first 4 weeks of treatment (P=0.004). The occurrence, but not the severity or the persistence, of both thrombocytopenia and leukopenia correlated significantly with SRL trough concentrations > or =16 ng/ml (P=0.001 and 0.0001, respectively). A significant correlation is evident between the occurrence of the two adverse effects (P=0.001). In 89% of patients, the first episode of either type of cytopenia resolved spontaneously. Among the remaining 11%, 7% responded to SRL dose reduction, and 4% to temporary suspension. No patient required permanent cessation of SRL therapy. Most patients experienced repeated, but self-limited, episodes of toxicity.

CONCLUSION

Thrombocytopenia and leukopenia are not infrequent occurrences with SRL treatment, and they generally resolve spontaneously.

Sirolimus in association with mycophenolate mofetil induction for the prevention of acute graft rejection in renal allograft recipients

INTRODUCTION

A previous trial in renal transplantation comparing sirolimus (rapamycin) to cyclosporine (CsA) in a triple-drug therapy regimen with azathioprine and corticosteroids found that the incidence of acute rejection was similar (approximately 40%) with a trend for better renal function with sirolimus.

METHODS

In 14 European centers, first cadaveric renal allograft recipients were randomized to receive sirolimus (n = 40) or CsA (n = 38) in an open-label design. All patients received corticosteroids and mycophenolate mofetil 2 g/day. Sirolimus and CsA were concentration controlled; trough levels of mycophenolic acid and prednisolone were also measured.

RESULTS

At 12 months, graft survival (92.5% sirolimus vs. 89.5% CsA), patient survival (97.5% sirolimus vs. 94.7% CsA), and the incidence of biopsy-proven acute rejection (27.5% sirolimus vs. 18.4% CsA) were not statistically different. The use of antibodies to treat suspected rejection episodes was also similar (7.5% sirolimus vs. 5.3% CsA). More sirolimus patients received bolus steroid therapy (20 vs. 11, P = 0.068). From month 2 onward, the calculated glomerular filtration rate was consistently higher in sirolimus-treated patients. The adverse events reported more frequently with sirolimus were thrombocytopenia (45% vs. 8%) and diarrhea (38% vs. 11%). In the CsA group, increased creatinine (18% vs. 39%), hyperuricemia (3% vs. 18%), cytomegalovirus infection (5% vs. 21%), and tremor (5% vs. 21%) were observed significantly more often.

DISCUSSION

Patient and graft survival and the incidence of biopsy-proven acute rejection at 12 months were comparable between sirolimus and CsA, whereas safety profiles were different. These data suggest that sirolimus may be used as primary therapy for the prevention of acute rejection.

Maintenance immunosuppression: new agents and persistent dilemmas

Since the approval of cyclosporine in 1983, only 3 drugs, mycophenolate mofetil, tacrolimus, and sirolimus, have been approved for maintenance immunosuppression in renal transplant recipients. All 3 agents decrease the incidence of early acute allograft rejection. An increase in intermediate and long-term graft survival has not been shown. However, survival data from these clinical trials should be interpreted with caution because the studies were not designed for this purpose. All 3 drugs have significant, albeit different, safety profiles. It remains to be seen whether, the lower incidence of hypertension and hyperlipidemia seen in tacrolimus-treated patients will reduce the incidence and severity of the cardiovascular disease experienced by renal transplant recipients. Sirolimus causes severe hyperlipidemia, and the long-term consequences both on the pathogenesis of cardiovascular disease and on lipid-associated renal injury have yet to be determined. Tacrolimus and mycophenolate mofetil appear to increase graft survival in pancreas-kidney recipients but their efficacy in another high-risk group, African-American recipients, has not yet been clearly shown. However, the trend toward improved graft survival in African-American recipients treated with tacrolimus is encouraging. Steroid-withdrawal remains a goal in the posttransplant period. The available data from steroid-withdrawal and steroid-avoidance clinical trials are mixed. Steroid withdrawal can be achieved in about 50% of patients on a cyclosporine-based immunosuppression regimen. Steroid-withdrawal under coverage of tacrolimus, mycophenolate mofetil or Neoral (Novartis Pharmaceuticals, East Hanover, NJ) may be more successful than that achieved in patients receiving Sandimmune (Novartis Pharmaceuticals). Further studies are needed in this area.

Therapeutic drug monitoring of sirolimus: correlations with efficacy and toxicity

We sought to examine the potential benefits of therapeutic drug monitoring of sirolimus, a potent immunosuppressive agent that displays a pleiotropic array of side effects.

METHODS

A high-performance liquid chromatography (LC) procedure combined with ultraviolet detection (UV) was used to measure serial concentrations of parent compound sirolimus in 150 renal transplant recipients over a period of 4 yr. Drug concentrations in whole blood at trough time, as well as within pharmacokinetic profiles, were correlated with clinical events using contingency tables, logistic regression analysis, and receiver operating characteristic (ROC) curves.

RESULTS

The LC/UV method showed an excellent correlation with detection of LC-resolved components by tandem mass spectrometry, demonstrating that the LC/UV method selectively detected parent compound. Sirolimus displayed the characteristics of a critical-dose drug: Its concentration could not be predicted by a standard body or demographic measure, or by dose, and it showed high degrees of intra- and inter-individual variability. However, there was a good correlation between trough and area-under-the-curve measurements. There was a significant association between trough values expressed as either observed ( < 5 ng/mL) or dose-corrected parameter ( < 1.7 ng/mL per mg administered drug) and the occurrence and severity of acute rejection episodes - despite the low overall incidence of 23 episodes among the cohort of 150 patients. Similarly, ROC functions showed a correlation of the occurrence of hypertriglyceridemia, thrombocytopenia, and leukopenia, but not hypercholesterolemia, with trough concentrations above 15 ng/mL.

CONCLUSION

Due to its behavior as a critical-dose drug, therapeutic monitoring to measure sirolimus concentrations by a LC/UV method may provide clinicians with a tool to optimize outcomes.

Sirolimus: a new agent for prevention of renal allograft rejection

The pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosage and administration of sirolimus are reviewed. Sirolimus can be used as an adjunct to cyclosporine and corticosteroids for preventing organ rejection in renal allograft recipients. It appears to block cell-cycle progression in the mid-to-late G1 phase; it also inhibits interleukin-2-dependent and independent proliferation of B-lymphocytes and production of immunoglobulins A, M, and G. Sirolimus is extensively metabolized by the liver and undergoes O-demethylation and hydroxylation. The mean oral clearance is 208 +/- 95 mL/hr/kg with an elimination half-life of 57 to 63 hours in kidney transplant recipients. Sirolimus is poorly absorbed from the gastrointestinal tract; its apparent oral bioavailability is about 15%. Two pivotal Phase III, multicenter, randomized, double-blind trials evaluating the efficacy of sirolimus in the prophylaxis of acute renal allograft rejection after transplantation have been conducted. A significant reduction in the occurrence of acute rejection was noted in both trials compared with azathioprine- or placebo-treated patients. Also, both sirolimus groups required significantly less antibody therapy for treatment of rejection. The primary adverse effects associated with sirolimus therapy include hypercholesterolemia and hypertriglyceridemia. Hypertension, diarrhea, increased creatinine, hypokalemia, arthralgia, rash, acne, leukopenia, and thrombocytopenia have also been observed. The labeled recommendations are a 6-mg loading dose as soon as possible after transplantation and a maintenance dose of 2 mg per day. Sirolimus is a potent novel immunosuppressive agent with proven efficacy in the prevention of acute rejection after renal transplantation. Use of sirolimus may lead to effective therapeutic strategies for sparing the use of cyclosporine and corticosteroids.

Sirolimus, a new potent immunosuppressant agent for refractory cardiac transplantation rejection: two case reports

Rejection remains a major cause of both early and late morbidity and mortality following heart transplantation despite major advances in immunosuppressive therapy. A major hurdle in the successful management of patients who have undergone heart transplantation is preventing and treating graft rejection. Cyclosporine, mycophenolate mofetil, azathioprine, tacrolimus (FK506) and OKT3 are well documented, effective immunosuppressive medications that prevent and treat acute or chronic rejection following heart transplantation. One of the macrolide antibiotics, sirolimus, is known to have immunosuppressant activity. In two patients with chronic rejection of cardiac grafts refractory to usual antirejection medications, sirolimus was successfully used to suppress graft rejection. Both patients continued to be rejection free after 10 months of sirolimus treatment despite significant decreases in doses of other immunosuppressants.

Sirolimus reduces the incidence of acute rejection episodes despite lower cyclosporine doses in caucasian recipients of mismatched primary renal allografts: a phase II trial. Rapamune Study Group

BACKGROUND

The novel agent sirolimus (SRL; Rapamune; rapamycin) inhibits the immune response by a mechanism distinct from those of calcineurin antagonists or antimetabolites. This randomized, controlled, multicenter, single blind, phase II trial examined the combination of SRL, steroids, and full versus reduced doses of cyclosporine (CsA) for prophylaxis of acute renal allograft rejection.

METHODS

A total of 149 recipients of mismatched cadaveric- or living-donor primary renal allografts were randomized into six groups. Three groups received placebo or 1 or 3 mg/m2/day SRL, as well as steroids and full-dose CsA (Sandimmune). Three groups received steroids, reduced-dose CsA (target trough level 50% of full-dose range), and 1, 3, or 5 mg/m2/day SRL.

RESULTS

The incidence of biopsy-proven acute rejection episodes within the first 6 months after transplant was reduced from 32.0% in the control group to 8.5% in patients receiving SRL (1 or 3 mg/m2/day) and full-dose Sandimmune CsA (P=0.018). Similar low rates of acute rejection episodes were observed among non-African-Americans, but not African-Americans, treated with SRL and reduced-dose Sandimmune CsA. Despite the augmented immunosuppression, 1-year patient and graft survival rates did not differ significantly across groups. Adverse effects attributable to CsA, including hypertension and new-onset diabetes mellitus, were not exacerbated by SRL. Except for an increased incidence of pneumonia among patients receiving full-dose CsA and 3 mg/m2/day SRL, the incidences of opportunistic infections were similar in all treatment groups. Although SRL produced more frequent, but reversible, hematological and lipid abnormalities, it had no apparent nephrotoxic effects to exacerbate CsA-induced renal dysfunction.

CONCLUSIONS

SRL in combination with CsA and steroids not only lowers the incidence of biopsy-proven acute renal allograft rejection episodes, but also may permit CsA sparing, at least among Caucasian patients, without an increased risk of rejection.

Entry-into-human study with the novel immunosuppressant SDZ RAD in stable renal transplant recipients

AIMS

To evaluate the tolerability of single oral SDZ RAD doses in stable renal transplant recipients and the pharmacokinetics of ascending SDZ RAD doses when coadministered with steady-state cyclosporin A microemulsion (Neoral).

METHODS

This randomized, double-blind, placebo-controlled, sequential study involved 54 patients in six treatment groups; a different SDZ RAD dose (0.25, 0. 75, 2.5, 7.5, 15, 25 mg) was assessed in each group. Patients received a single oral dose of SDZ RAD (n=6) or placebo (n=3) with their usual Neoral dose. SDZ RAD and cyclosporin A pharmacokinetic parameters were determined.

RESULTS

All SDZ RAD doses were well tolerated, with no discontinuations due to adverse events, serious adverse events, or deaths. Similar proportions of patients receiving SDZ RAD and placebo had at least one adverse event (44% and 50%, respectively). Mean changes in laboratory variables (baseline to endpoint) showed no clinically meaningful differences between SDZ RAD and placebo groups. SDZ RAD was absorbed rapidly and showed dose-proportional pharmacokinetics (dose: 2.5-25 mg), based on systemic exposure. Multiple postabsorptive phases in the pharmacokinetic profile indicate tissue distribution. The elimination half-life ranged from 24 to 35 h across the five highest dose groups. Pharmacokinetics were similar in men and women. Co-administration of escalating single oral SDZ RAD doses did not affect steady-state cyclosporin A pharmacokinetics.

CONCLUSIONS

SDZ RAD was well tolerated; safety profiles of SDZ RAD and placebo were similar. SDZ RAD pharmacokinetics were dose-proportional across the range 2.5-25 mg in conjunction with cyclosporin A-based therapy, according to systemic exposure. Cyclosporin A pharmacokinetics were not affected by coadministration of single oral doses of 0.25-25 mg SDZ RAD.

A phase I study of a 4-week course of SDZ-RAD (RAD) quiescent cyclosporine-prednisone-treated renal transplant recipients

BACKGROUND AND METHODS

This phase I, randomized, blinded, placebo-controlled study assessed the safety profile and pharmacokinetics of a 4-week course of once-daily, sequential ascending doses (0.75, 2.5, or 7.5 mg/day) of SDZ-RAD (RAD) capsules in renal transplant recipients on a stable regimen of cyclosporine (CsA; Neoral) and prednisone.

RESULTS

RAD displayed a similar spectrum of side effects as observed with rapamycin, namely, an increased incidence of infection associated with the augmented immunosuppression and a dose-related occurrence of thrombocytopenia, hypercholesterolemia, and hypertriglyceridemia, particularly at the 7.5-mg dose. The pharmacokinetic parameters of RAD showed dose proportionality, a good correlation between trough and area under the curve (AUC) concentrations, and a moderate accumulation of 2.5-fold. The drug was absorbed within 2 hr and displayed a 16-19-hr half-life, which is shorter than that of rapamycin. RAD reached steady state at 4 days. Preliminary kinetic-dynamic correlations indicate a correlation between thrombocytopenia (but not hyperlipidemia) and AUC, as well as maximum drug concentrations, and weight-adjusted dose. At the end of a 4-week course of simultaneous dosing, there was no evidence of a pharmacokinetic interaction between CsA and RAD.

CONCLUSION

This study suggests that the shorter half-life of RAD compared to rapamycin may confer the benefits of rapid attainment of steady state and dissipation of effects upon drug cessation. Controlled, multicenter trials are being planned to assess the impact of these features on clinical outcomes.

The potential role of rapamycin in pediatric transplantation as observed from adult studies

Although pediatric patient and renal graft survival rates have shown marked improvements during the past decade, the persistent toxicities of immunosuppressive drugs and chronic allograft attrition remain major obstacles in transplant therapy. Results in adult patients suggest that complete steroid withdrawal is possible in the majority of recipients under treatment with a cyclosporin A-rapamycin (CsA RAPA) regimen. Furthermore, preliminary studies suggest that a marked reduction in the dose of CsA may be possible under the umbrella of RAPA coverage. The gain in immunosuppressive efficacy afforded by RAPA has not only been obtained without an increased morbidity owing to infectious or neoplastic causes, but also with the potential for reducing the incidence and/or progression of chronic rejection.

Systemic toxicity following administration of sirolimus (formerly rapamycin) for psoriasis: association of capillary leak syndrome with apoptosis of lesional lymphocytes

BACKGROUND

Sirolimus (formerly rapamycin) is an immunosuppressive agent that interferes with T-cell activation. After 2 individuals with psoriasis developed a capillary leak syndrome following treatment with oral sirolimus lesional skin cells and activated peripheral blood cells were analyzed for induction of apoptosis.

OBSERVATIONS

A keratome skin specimen from 1 patient with sirolimus-induced capillary leak syndrome had a 2.3-fold increase in percentage of apoptotic cells (to 48%) compared with an unaffected sirolimus-treated patient with psoriasis (21%). Activated peripheral blood T cells from patients with psoriasis tended to exhibit greater spontaneous or dexamethasone-induced apoptosis than did normal T cells, particularly in the presence of sirolimus.

CONCLUSIONS

Severe adverse effects of sirolimus include fever, anemia, and capillary leak syndrome. These symptoms may be the result of drug-induced apoptosis of lesional leukocytes, especially activated T lymphocytes, and possibly release of inflammatory mediators. Because patients with severe psoriasis may develop capillary leak from various systemic therapies, clinical monitoring is advisable for patients with inflammatory diseases who are treated with immune modulators.

Sirolimus (rapamycin)-based therapy in human renal transplantation: similar efficacy and different toxicity compared with cyclosporine. Sirolimus European Renal Transplant Study Group

BACKGROUND

Sirolimus (rapamycin) is a potent immunosuppressant with a mechanism of action different from cyclosporine (CsA) or tacrolimus.

METHODS

In 11 European centers, first cadaveric renal allograft recipients were randomized to CsA (n=42) or sirolimus (n=41). Dosing of these agents was concentration-controlled and open-labeled. All patients received corticosteroids and azathioprine.

RESULTS

At 12 months, graft survival (98% sirolimus vs. 90% CsA), patient survival (100% vs. 98%), and incidence of biopsy-confirmed acute rejection (41% vs. 38%) were similar. Serum creatinine was lower with sirolimus, significantly (P< or =0.05) so at 3 and 4 months, and serum uric acid and magnesium were normal. Laboratory abnormalities reported significantly more often with sirolimus included hypertriglyceridemia (51% vs. 12%), hypercholesterolemia (44% vs. 14%), thrombocytopenia (37% vs. 0%), leukopenia (39% vs. 14%), and, of lesser importance, increased liver enzymes and hypokalemia. These abnormalities improved 2 months after transplantation when the sirolimus target trough level was lowered from 30 to 15 ng/ml. Occurrence of cytomegalovirus was comparable (14% vs. 12%); incidences of herpes simplex (24% vs. 10%, P=0.08) and pneumonia (17% vs. 2%, P=0.03) were higher with sirolimus. No gingival hyperplasia was seen with sirolimus, tremor was rare, and hypertension was less frequent (17% vs. 33%). Two malignancies were observed with CsA and none with sirolimus.

CONCLUSIONS

Results at 12 months suggest that sirolimus can be used as base therapy in the prophylaxis of acute renal transplant rejection, and has a safety profile that differs from CsA.

Sirolimus: a potent new immunosuppressant for liver transplantation

BACKGROUND

Sirolimus (rapamycin) is a new immunosuppressant that appears to be synergistic with cyclosporine in kidney transplantation, but with a different side-effect profile. This pilot study evaluated sirolimus in liver transplantation.

METHODS

Patients undergoing orthotopic liver transplantation for primary tumors (8), and later for nonmalignant disease (7), received one of three sirolimus-based immunosuppressive regimens. Protocol A comprised sirolimus, microemulsion cyclosporine (target whole blood concentration: 100 ng/ml), and prednisolone; protocol B omitted prednisolone; and protocol C was sirolimus alone. By 3 months after transplantation, all patients were receiving sirolimus as monotherapy.

RESULTS

Fifteen patients were treated with a follow-up of 117-806 days. Rejection was more common on monotherapy than double therapy, and absent on triple therapy. The drug was generally well tolerated, with only three patients discontinuing sirolimus: one for hyperlipidemia, one for pneumocystis pneumonia, and one for inability to tolerate the taste of the drug. Two patients discontinued cyclosporine early, both as a result of neurological complications; they continued on sirolimus monotherapy. Five patients died; one suffered a cardiac arrest, and four died from sepsis in association with graft-versus-host disease, recurrent tumor, a paralyzed right hemidiaphragm, and primary nonfunction.

CONCLUSIONS

Sirolimus combined with cyclosporine provided potent immunosuppression of liver allografts, and sirolimus monotherapy was adequate and well tolerated as maintenance therapy. Side effects of sirolimus over the short period of follow-up were uncommon and reversible with dose reduction or cessation of therapy.

Effect of combined immunosuppressive drug therapy on small intestinal nutrient transport in the rat

OBJECTIVE

Prevention of rejection and preservation of graft function remain as obstacles to clinical small intestinal transplantation (SIT). This study evaluated the effects of combined immunosuppressive agents (FK506, Rapamycin, and Mycophenolate Mofetil) on intestinal function and animal well being.

METHODS

Screening for additive toxicity was done in experiment one (D1, n = 10); doses were: FK506 0.3 mg/kg/d, Rapamycin 2 mg/kg/d, and Mycophenolate Mofetil 20 mg/kg/d, orally once daily. Control animals (C1, n = 10) received equivalent vehicle. In the second phase of the experiment, the effect of an additional parenteral treatment phase was investigated, with drug treated animals (D2, n = 6) received FK506 0.3 mg/kg, Rapamycin 1 mg/kg, and Mycophenolate Mofetil 10 mg/kg sq q12h for 1 week followed by FK506 3 mg/kg, Rapamycin 1 mg/kg, and Mycophenolate Mofetil 10 mg/kg p.o. q12h for 4 weeks. Control animals (C2, n = 6) received equivalent vehicle. Parameters followed were weight gain, nutrient absorption, drug levels and nutrient transport in vitro.

RESULTS

Controls grew normally, while weight gain was significantly reduced in drug treated animals: This was paralleled by a reduction in dietary fat absorption. Drug levels were low to therapeutic for all drugs in both experiments; FK506 appeared to affect Rapamycin and Mycophenolate Mofetil metabolism, increasing levels of both as FK506 doses increased. Nutrient transport was either not effected (D1) or increased (D2).

CONCLUSIONS

We conclude that low dose combination immunosuppressive therapy inhibits weight gain, without affecting absorption of dietary energy, or adversely affecting glucose transport. We postulate a systemic metabolic cause, which requires additional investigation at the cellular level; additional studies are also required to determine if the additive immunosuppression outweigh the side effects for SIT.

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.

The nephrotoxicity of new and old immunosuppressive drugs

The above snapshot of the relevant literature on chronic Cyclosporine and Tacrolimus nephropathy indicate fertile areas for further study. The reader is referred to recent reviews for a more in-depth analysis of this problem (2).