Selective immunosuppressive agents. ATC Code:
Everolimus, a proliferation signal inhibitor, prevents allograft rejection in rodent and non-human primate models of allotransplantation. It exerts its immunosuppressive effect by inhibiting the antigen-activated T-cell proliferation, and thus clonal expansion, driven by T-cell-specific interleukins eg, interleukin-2 and interleukin-15. Everolimus inhibits an intracellular signaling pathway that normally leads to cell proliferation when triggered by the binding of these T-cell growth factors to their receptors. The blockage of this signal by everolimus causes cells to be arrested at the G1 stage of the cell cycle.
At the molecular level, everolimus forms a complex with the cytoplasmic protein FKBP-12. In the presence of everolimus the growth factor-stimulated phosphorylation of the p70, S6 kinase is inhibited. Since p70 S6 kinase phosphorylation is under the control of FRAP (also called m-TOR), this finding suggests that the everolimus-FKBP-12 complex binds to and thus, interferes with the function of FRAP. FRAP is a key regulatory protein which governs cell metabolism, growth and proliferation; disabling FRAP function thus explains the cell cycle arrest caused by everolimus.
Everolimus, thus, has a different mode of action than ciclosporin. In preclinical models of allotransplantation, the combination of everolimus and ciclosporin was more effective than either compound alone.
The effect of everolimus is not restricted to T-cells. Everolimus generally inhibits growth-factor-stimulated proliferation of hematopoietic cells and non-hematopoietic cells such as vascular smooth muscle cells. Growth-factor-stimulated proliferation of vascular smooth muscle cells, triggered by injury to endothelial cells and leading to neointima formation, plays a key role in the pathogenesis of chronic rejection. Preclinical studies with everolimus have shown inhibition of neointima formation in a rat aorta allotransplantation model.
Clinical Studies: Kidney Transplantation:
Everolimus in fixed doses of 1.5 mg/day and 3 mg/day, in combination with standard doses of ciclosporin for microemulsion and corticosteroids was investigated in 2 phase III de novo
renal transplant trials (B201 and B251). Mycofenolate mofetil (MMF) 1 g twice daily was used as comparator. The co-primary composite endpoints were efficacy failure (biopsy-proven acute rejection, graft loss, death or loss to follow-up) at 6 months and graft loss, death or loss to follow-up at 12 months. Certican was, overall, non-inferior to MMF in these trials. In the B201 study, the incidence of biopsy-proven acute rejection at 6 months in the Certican 1.5 mg/day, Certican 3 mg/day and MMF groups was 21.6%, 18.2% and 23.5%, respectively. In the B251 study, the incidence for the Certican 1.5 mg/day, Certican 3 mg/day and MMF groups was 17.1%, 20.1% and 23.5%, respectively.
Reduced allograft function with elevated serum creatinine was observed more frequently among subjects using Certican in combination with full dose ciclosporin for microemulsion than in MMF patients. This effect suggests that Certican increases ciclosporin nephrotoxicity. This may be reversible with ciclosporin dose reduction.
Two phase III b studies (A2306 and A2307) evaluated the efficacy and safety of Certican 1.5 mg/day and 3 mg/day (initial dosing; subsequent dosing based on target trough concentration (C0) ≥3 ng/mL) in combination with reduced exposure to ciclosporin (monitored by C2) in de novo
transplant recipients. In A2306, target C2 concentrations were 1000-1400 ng/mL in weeks 0-4, 700-900 ng/mL in weeks 5-8, 550-650 ng/mL in weeks 9-12, 350-450 ng/mL in weeks 13-52. In A2307 (combination with Simulect), target C2 concentrations were 500-700 ng/mL in weeks 0-8 and 350-450 ng/mL in weeks 9-52.
Actual trough concentrations (C0) and C2 for A2306 are provided in the table as follows: (See Table 1.)
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In A2306, 12-month results for the incidence of biopsy-proven rejection in the ITT population (N=237; 112 on Certican 1.5 mg/day and 125 on 3 mg/day) were 25.9% for the 1.5 mg/day group and 19.2% for the 3 mg/day group. Cross-study comparisons indicated that allograft function was better than that seen with Certican in studies involving full-dose ciclosporin. On-treatment median serum creatinine values at month 12 were 122 micromol/L in the 1.5 mg and 126 micromol/L in the 3-mg Certican group (mean: 126 and 134 micromol/L). On-treatment median creatinine clearance values according to Cockcroft-Gault were 69 and 62 mL/min in the 2 Certican groups (mean: 69 and 65 mL/min).
The A2307 study is similar in design to A2306, with the addition of two 20-mg doses of basiliximab at day 0 and day 4 and with lower target C2 levels for ciclosporin through the first 8 weeks following transplantation (weeks 0-8: 500-700 ng/mL, months 3-12: 350-450 ng/mL). Analyses of the 12-month results (ITT, N=256; 117 on Certican 1.5 mg/day and 139 on 3 mg/day) demonstrated incidences of biopsy-proven rejection of 13.7% for the 1.5 mg/day group and 15.8% for the 3 mg/day group. On-treatment median serum creatinine values at month 12 were 128 micromol/L in the 1.5mg and 126 micromol/L in the 3 mg Certican group (mean: 132 and 132 micromol/L). On-treatment median creatinine clearance values according to Cockcroft-Gault were 64 and 65 mL/min in the 2 Certican groups (mean: 68 and 65 mL/min).
In the phase III heart study (B253), Certican 1.5 mg/day and 3 mg/day, in combination with standard doses of ciclosporin for microemulsion and corticosteroids, were both compared with azathioprine (AZA) 1-3 mg/kg/day. The primary endpoint was a composite of the incidence of the following acute rejection ≥ ISHLT grade 3A, acute rejection associated with hemodynamic compromise, graft loss, patient death or loss to follow-up at 6, 12 and 24 months. The incidence of biopsy-proven acute rejection ≥ISHLT grade 3A at month 6 was 27.8% for the 1.5-mg/day group, 19% for the 3-mg/day group and 41.6% for the AZA group, respectively (p=0.003 for 1.5 mg vs control; <0.001 for 3 mg vs control).
Based on coronary artery IV ultrasound data obtained from a subset of the study population, both Certican doses were statistically significantly more effective than AZA in preventing allograft vasculopathy (defined as an increase in maximum intimal thickness from baseline ≥0.5 mm in at least 1 matched slice of an automated pullback sequence), an important risk factor for long-term graft loss.
Ciclosporin doses were based on target trough levels (C0) as follows: Weeks 1-4: 250-400 ng/mL, months 1-6: 200-350 ng/mL, months 7-24: 100-300 ng/mL.
Actual trough concentrations (C0) are in the table as follows: (See Table 2.)
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Elevated serum creatinine was observed more frequently among subjects using Certican in combination with full dose of ciclosporin for microemulsion than in AZA patients. This effect suggests that Certican increases the ciclosporin-induced nephrotoxicity. This may be reversible with ciclosporin dose reduction, nevertheless, there are limited data regarding dosing Certican with ciclosporin trough concentrations (C0) <100 ng/mL after 6 months in cardiac transplantation.
Peak everolimus concentrations are reached 1-2 hrs after administration of an oral dose. Everolimus blood concentrations in transplant patients are dose-proportional over the dose range of 0.25-15 mg. The relative bioavailability of the dispersible tablet compared with the conventional tablet is 0.9 (90% CI 0.76-1.07) based on the AUC ratio.
and AUC of everolimus are reduced by 60% and 16%, respectively, when the tablet formulation is given with a high-fat meal. To minimize variability, Certican should either be consistently taken with food or consistently taken without it.
The blood-to-plasma ratio of everolimus, which is concentration-dependent over the range of 5-5000 ng/mL, is 17-73%. Plasma protein-binding is approximately 74% in healthy subjects and patients with moderate hepatic impairment. The distribution volume associated with the terminal phase (Vz/F) in maintenance renal transplant patients is 342±107 L.
Everolimus is a substrate of CYP3A4 and P-glycoprotein. The main metabolic pathways identified in man were monohydroxylations and O-dealkylations. Two main metabolites were formed by hydrolysis of the cyclic lactone. Everolimus was the main circulating component in the blood. None of the main metabolites are likely to contribute significantly to the immunosuppressive activity of everolimus.
After a single dose of radiolabelled everolimus in transplant patients receiving ciclosporin, most of the radioactivity (80%) was recovered from the feces and only a minor amount (5%) was excreted in urine. Parent drug was not detected in the urine or feces.
The pharmacokinetics were comparable in kidney and heart transplant patients receiving everolimus twice daily with ciclosporin for microemulsion. Steady-state is reached by day 4, with a 2- to 3-fold accumulation in blood levels as compared with exposure after the first dose. Tmax
occurs at 1-2 hrs post-dose. At 0.75 and 1.5 mg twice daily, Cmax
averages 11.1±4.6 and 20.3±8 ng/mL, respectively, and AUC averages 75±31 and 131±59 ng·hr/mL, respectively. At 0.75 and 1.5 mg twice daily, predose trough blood levels (Cmin
) average 4.1±2.1 and 7.1±4.6 ng/mL, respectively. Everolimus exposure remains stable over time in the first post-transplant year. Cmin
is significantly correlated with AUC, yielding a correlation coefficient between 0.86 and 0.94. Based on analysis of population pharmacokinetics, oral clearance (CL/F) is 8.8 L/hr (27% interpatient variation) and the central distribution volume (Vc/F) is 110 L (36% interpatient variation). Residual variability in blood concentrations is 31%. The elimination half-life is 28±7 hrs.
The average AUC of everolimus in 8 patients with moderate hepatic impairment (Child-Pugh class B) was twice as high as that found in 8 healthy subjects. AUC was positively correlated with serum bilirubin concentration and with prolongation of prothrombin time and negatively correlated with serum albumin concentration. The AUC of everolimus tended to be greater than that in healthy subjects if bilirubin was >34 micromol/L and/or albumin concentration was <35 g/L. The impact of severe hepatic impairment (Child-Pugh class C) has not been assessed but the effect on the AUC of everolimus is likely to be as large as, or larger than, the effect of moderate impairment (see Dosage & Administration).
Post-transplant renal impairment (Clcr
range; 11-107 mL/min) did not affect the pharmacokinetics of everolimus.
Everolimus CL/F increased in a linear manner with patient age (1-16 years), body surface area (0.49-1.92 m2
) and weight (11-77 kg). Steady-state CL/F was 10.2±3 L/hr/m2
and elimination half-life was 30±11 hrs. Nineteen pediatric de novo
renal transplant patients (1-16 years) received Certican dispersible tablets at a dose of 0.8 mg/m2
(max 1.5 mg) twice daily with ciclosporin for microemulsion. They achieved an everolimus AUC of 87±27 ng·hr/mL which is similar to adults receiving 0.75 mg twice daily. Steady-state trough levels (C0) were 4.4±1.7 ng/mL.
A limited reduction in everolimus oral CL of 0.33%/year was estimated in adults (age range studied was 16-70 years). No dose adjustment is considered necessary.
Based on analysis of population pharmacokinetics, oral clearance (CL/F) is, on average, 20% higher in Black transplant patients (see Dosage & Administration).
The average everolimus trough concentration (C0) over the first 6 months post-transplant was related to the incidence of biopsy-confirmed acute rejection and of thrombocytopenia in kidney and heart transplant patients (see Table 3).
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Toxicology: Preclinical Safety Data:
In a kidney transplantation model in cynomolgus monkeys, rejection occurred within 4-8 days in untreated animals. With administration of everolimus, rejection could be delayed until day 27 (median); the range was 8-91 days. At the higher dose of 1.5 mg/kg, the median rose to 59 days and the range was 28-85 days. With the comparator substance rapamycin, the median was 43 days (range 5-103 days) at the 0.75 mg/kg dose and 56 days (range 8-103 days) at the 1.5 mg/kg dose. It should be noted that prevention of rejection over the whole 103-day reporting period was only possible in 3 of 8 treated monkeys in the 1.5 mg/kg rapamycin group.
There was no statistically significant difference between the 2 treatment groups.
In animal studies, everolimus showed a low acute toxic potential. Following single oral doses of 2000 mg/kg (limit test), lethality or severe toxicity was not observed in mice or rats.
The preclinical safety profile of everolimus was assessed in mice, rats, minipigs, monkeys and rabbits. The major target organs were male and female reproductive systems (testicular tubular degeneration, reduced sperm content in epididymides and uterine atrophy) in several species and only in rats, lungs (increased alveolar macrophages) and eyes (lenticular anterior suture line opacities). Minor kidney changes were seen in the rat (exacerbation of age-related lipofuscin in tubular epithelium and the mouse exacerbation of background lesions). There was no indication of kidney toxicity in monkeys or minipigs.
Everolimus appeared to exacerbate spontaneously background diseases (chronic myocarditis in rats, coxsackie virus infection of plasma and heart in monkeys, coccidian infestation of GI tract in minipigs, skin lesions in mice and monkeys). These findings were generally observed at systemic exposure levels within the range of therapeutic exposure or above, with the exception of findings in rats, which occurred below therapeutic exposure due to a high tissue distribution.
Ciclosporin in combination with everolimus caused higher systemic exposure to everolimus and increased toxicity. There were no new target organs in the rat. Monkeys showed hemorrhage and arthritis in several organs. Histopathological findings in the kidney were also diagnosed.
In a male fertility study in rats, testicular morphology was affected at ≥0.5 mg/kg, and sperm motility, sperm head count and plasma testosterone levels were diminished at 5 mg/kg which is within the range of therapeutic exposure and caused a decrease in male fertility. There was evidence of reversibility. Female fertility was not affected, but everolimus crossed the placenta and was toxic to the conceptus. In rats, everolimus caused embryo/fetotoxicity, at systemic exposure below the therapeutic one, that was manifested as mortality and reduced fetal weight. The incidence of skeletal variations and malformations at 0.3 and 0.9 mg/kg (eg, sternal cleft) was increased. In rabbits, embryotoxicity was evident by an increase in late resorptions.
Genotoxicity studies covering relevant genotoxicity end-points showed no evidence of clastogenic or mutagenic activity. Administration of everolimus for up to 2 years did not indicate any oncogenic potential in mice and rats up to the highest doses corresponding respectively to 8.6 and 0.3 times the estimated clinical exposure.