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Simulect

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Simulect

Simulect

CLINICAL PHARMACOLOGY

General

Mechanism of Action: Basiliximab functions as an IL-2 receptor antagonist by binding with high affinity (Ka = 1 x 1010 M-1) to the alpha chain of the high affinity IL-2 receptor complex and inhibiting IL-2 binding. Basiliximab is specifically targeted against IL-2Rα, which is selectively expressed on the surface of activated T-lymphocytes. This specific high affinity binding of Simulect® (basiliximab) to IL-2Rα competitively inhibits IL-2-mediated activation of lymphocytes, a critical pathway in the cellular immune response involved in allograft rejection. While in the circulation, Simulect (basiliximab) impairs the response of the immune system to antigenic challenges. Whether the ability to respond to repeated or ongoing challenges with those antigens returns to normal after Simulect is cleared is unknown (see PRECAUTIONS).

Pharmacokinetics

Adults: Single-dose and multiple-dose pharmacokinetic studies have been conducted in patients undergoing first kidney transplantation. Cumulative doses ranged from 15 mg up to 150 mg. Peak mean SD serum concentration following intravenous infusion of 20 mg over 30 minutes is 7.1 5.1 mg/L. There is a dose-proportional increase in Cmax and AUC up to the highest tested single dose of 60 mg. The volume of distribution at steady state is 8.6 4.1 L. The extent and degree of distribution to various body compartments have not been fully studied. The terminal half-life is 7.2 3.2 days. Total body clearance is 41 19 mL/h. No clinically relevant influence of body weight or gender on distribution volume or clearance has been observed in adult patients. Elimination half-life was not influenced by age (20-69 years), gender or race (see DOSAGE AND ADMINISTRATION).

Pediatric: The pharmacokinetics of Simulect (basiliximab) have been assessed in 39 pediatric patients undergoing renal transplantation. In infants and children (1-11 years of age, n=25), the distribution volume and clearance were reduced by about 50% compared to adult renal transplantation patients. The volume of distribution at steady state was 4.8 2.1 L, half-life was 9.5 4.5 days and clearance was 17 6 mL/h. Disposition parameters were not influenced to a clinically relevant extent by age (1-11 years of age), body weight (9-37 kg) or body surface area (0.44-1.20 m2) in this age group. In adolescents (12-16 years of age, n=14), disposition was similar to that in adult renal transplantation patients. The volume of distribution at steady state was 7.8 5.1 L, half-life was 9.1 3.9 days and clearance was 31 19 mL/h (see DOSAGE AND ADMINISTRATION).

Pharmacodynamics

Complete and consistent binding to IL-2Rα in adults is maintained as long as serum Simulect (basiliximab) levels exceed 0.2 g/mL. As concentrations fall below this threshold, the IL-2Rα sites are no longer fully bound and the number of T-cells expressing unbound IL-2Rα returns to pretherapy values within 1-2 weeks. The relationship between serum concentration and receptor saturation was assessed in 13 pediatric patients and was similar to that characterized in adult renal transplantation patients. In vitro studies using human tissues indicate that Simulect (basiliximab) binds only to lymphocytes.

The duration of clinically relevant IL-2 receptor blockade after the recommended course of Simulect is not known. When basiliximab was added to a regimen of cyclosporine, USP (MODIFIED) and corticosteroids in adult patients, the duration of IL-2Rα saturation was 36 14 days (mean SD), similar to that observed in pediatric patients (36 14 days) (see DOSAGE AND ADMINISTRATION). When basiliximab was added to a triple therapy regimen consisting of cyclosporine, USP (MODIFIED), corticosteroids, and azathioprine in adults, the duration was 50 20 days and when added to cyclosporine, USP (MODIFIED), corticosteroids, and mycophenolate mofetil in adults, the duration was 59 17 days (see PRECAUTIONS: DRUG INTERACTIONS). No significant changes to circulating lymphocyte numbers or cell phenotypes were observed by flow cytometry.

Clinical Studies

The safety and efficacy of Simulect® (basiliximab) for the prophylaxis of acute organ rejection in adults following cadaveric- or living-donor renal transplantation were assessed in four randomized, double-blind, placebo-controlled clinical studies (1,184 patients). Of these four, two studies (Study 1 [EU/CAN] and Study 2 [US Study]) compared two 20-mg doses of Simulect (basiliximab) with placebo, each administered intravenously as an infusion, as part of a standard immunosuppressive regimen comprised of cyclosporine, USP (MODIFIED) and corticosteroids. The other two controlled studies compared two 20-mg doses of Simulect (basiliximab) with placebo, each administered intravenously as a bolus injection, as part of a standard triple-immunosuppressive regimen comprised of cyclosporine, USP (MODIFIED), corticosteroids and either azathioprine or mycophenolate mofetil (Study 3 and Study 4, respectively). The first dose of Simulect (basiliximab) or placebo was administered within 2 hours prior to transplantation surgery (Day 0) and the second dose administered on Day 4 post-transplantation. The regimen of Simulect (basiliximab) was chosen to provide 30-45 days of IL-2Rα saturation.

729 patients were enrolled in the two studies using a dual maintenance immunosuppressive regimen comprised of cyclosporine, USP (MODIFIED) and corticosteroids, of which 363 patients were treated with Simulect (basiliximab) and 358 patients were placebo-treated. Study 1 was conducted at 21 sites in Europe and Canada (EU/CAN Study); Study 2 was conducted at 21 sites in the USA (US Study). Patients 18-75 years of age undergoing first cadaveric- (Study 1 and Study 2) or living-donor (Study 2 only) renal transplantation, with ≥ 1 HLA mismatch, were enrolled.1,2

The primary efficacy endpoint in both studies was the incidence of death, graft loss or an episode of acute rejection during the first 6 months post-transplantation. Secondary efficacy endpoints included the primary efficacy variable measured during the first 12 months post-transplantation, the incidence of biopsy-confirmed acute rejection during the first 6 and 12 months post-transplantation, and patient survival and graft survival, each measured at 12 months post-transplantation. Table 1 summarizes the results of these studies. Figure 1 displays the Kaplan-Meier estimates of the percentage of patients by treatment group experiencing the primary efficacy endpoint during the first 12 months post-transplantation for Study 2. Patients in both studies receiving Simulect (basiliximab) experienced a significantly lower incidence of biopsy-confirmed rejection episodes at both 6 and 12 months post-transplantation. There was no difference in the rate of delayed graft function, patient survival, or graft survival between Simulect (basiliximab) -treated patients and placebo-treated patients in either study.

There was no evidence that the clinical benefit of Simulect (basiliximab) was limited to specific subpopulations based on age, gender, race, donor type (cadaveric or living donor allograft) or history of diabetes mellitus.

Table 1. Efficacy Parameters (Percentage of Patients)

Dual-therapy Regimen (cyclosporine*and corticosteroids)
Study 1 Study 2
Placebo
(N=185)
Simulect®
(N=190)
p-value Placebo
(N=173)
Simulect®
(N=173)
p-value
Primary endpoint
Death, graft loss or acute rejection episode (0-6months)
57% 42% 0.003 55% 38% 0.002
Secondary endpoints
Death, graft loss or acute rejection episode (0-12months)
60% 46% 0.007 58% 41% 0.001
Biopsy-confirmed rejection episode (0-6months)
44% 30% 0.007 46% 33% 0.015
Biopsy-confirmed rejection episode (0-12months)
46% 32% 0.005 49% 35% 0.009
Patient survival (12 months)
97% 95% 0.29 96% 97% 0.56
Patients with functioning graft (12 months)
87% 88% 0.70 93% 95% 0.50
* USP (MODIFIED)

Figure 1: Kaplan Meier Estimate of the Percentage of Subjects with Death, Graft Loss or First Rejection Episode (Dual Therapy) Month: 0-12

Kaplan Meier Estimate of the Percentage of Subjects with Death, Graft Loss or First Rejection Episode - Illustration

Two double-blind, randomized, placebo-controlled studies (Study 3 and Study 4) assessed the safety and efficacy of Simulect (basiliximab) for the prophylaxis of acute renal transplant rejection in adults when used in combination with a triple immunosuppressive regimen. In Study 3, 340 patients were concomitantly treated with cyclosporine, USP (MODIFIED), corticosteroids and azathioprine (AZA), of which 168 patients were treated with Simulect (basiliximab) and 172 patients were treated with placebo. In Study 4, 123 patients were concomitantly treated with cyclosporine, USP (MODIFIED), corticosteroids and mycophenolate mofetil (MMF), of which 59 patients were treated with Simulect (basiliximab) and 64 patients were treated with placebo. Patients 18-70 years of age undergoing first or second cadaveric or living donor (related or unrelated) renal transplantation were enrolled in both studies. The results of Study 3 are shown in Table 2.

These results are consistent with the findings from Study 1 and Study 2.

Table 2. Efficacy Parameters (Percentage of Patients)

Study 3: Triple-therapy Regimen (cyclosporine*, corticosteroids, andazathioprine)
  Placebo
(N=172)
Simulect®
(N=168)
p-value
Primary endpoint
  Acute rejection episode (0-6 months) 35% 21% 0.005
Secondary endpoints
  Death, graft loss or acute rejection episode (0-6 months) 40% 26% 0.008
  Biopsy-confirmed rejection episode (0-6 months) 29% 18% 0.023
  Patient survival (12 months) 97% 98% 1.000
  Patients with functioning graft (12 months) 88% 90% 0.599
*USP (MODIFIED)

In Study 4, the percentage of patients experiencing biopsy-proven acute rejection by 6 months was 15% (9 of 59 patients) in the Simulect (basiliximab) group and 27% (17 of 64 patients) in the placebo group. Although numerically lower, the difference in acute rejection was not significant.

In a multicenter, randomized, double-blind, placebo-controlled trial of Simulect (basiliximab) for the prevention of allograft rejection in liver transplant recipients (n=381) receiving concomitant cyclosporine, USP (MODIFIED) and steroids, the incidence of the combined endpoint of death, graft loss, or first biopsy-confirmed rejection episode at either 6 or 12 months was similar between patients randomized to receive Simulect (basiliximab) and those randomized to receive placebo.

The efficacy of Simulect (basiliximab) for the prophylaxis of acute rejection in recipients of a second renal allograft has not been demonstrated.

Long Term Follow-up

Five-year patient survival and graft survival data were provided by 71% and 58% of the original subjects of Study 1 and Study 2, respectively. Subjects in both studies continued to receive a dual-therapy regimen with cyclosporine, USP (MODIFIED) and corticosteroid. No difference was observed between groups in the 5-year graft survival in either Study 1 (91% Simulect (basiliximab) group, 92% placebo group) or Study 2 (85% Simulect (basiliximab) group, 86% placebo group). In Study 1, patient survival was lower in the Simulect (basiliximab) -treated patients compared to the placebo-treated patients (142/163 [87%] vs. 156/164 [95%], respectively). The cause of this difference in survival is unknown. The data do not indicate an increase in malignancy- or infection-related mortality. In Study 2, patient survival in the placebo group (90%) was the same compared to Simulect (basiliximab) group (90%).

REFERENCES

1. Kahan, B.D., Rajagopalan P.R. and Hall M., Transplantation, 67, 276-284 (1999).

2. Nashan, B., Moore R., Amlot P., Schmidt A.-G., Abeywickrama K. and Soulillou J.-P., Lancet 350, 1193-1198 (1997).

Last reviewed on RxList: 11/7/2008
This monograph has been modified to include the generic and brand name in many instances.

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