Source: European Medicines Agency (EU) Revision Year: 2019 Publisher: AbbVie Deutschland GmbH & Co. KG, Knollstrasse, 67061, Ludwigshafen, Germany
Pharmacotherapeutic group: immune sera immunoglobulins, specific immunoglobulins
ATC Code: J06BB16
Palivizumab is a humanised IgG1κ monoclonal antibody directed to an epitope in the A antigenic site of the fusion protein of respiratory syncytial virus (RSV). This humanised monoclonal antibody is composed of human (95%) and murine (5%) antibody sequences. It has potent neutralising and fusion-inhibitory activity against both RSV subtype A and B strains.
Palivizumab serum concentrations of approximately 30 μg/ml have been shown to produce a 99% reduction in pulmonary RSV replication in the cotton rat model.
The antiviral activity of palivizumab was assessed in a microneutralization assay in which increasing concentrations of antibody were incubated with RSV prior to addition of the human epithelial cells HEp-2. After incubation for 4-5 days, RSV antigen was measured in an enzyme-linked immunosorbent assay (ELISA). The neutralization titre (50% effective concentration [EC50]) is expressed as the antibody concentration required to reduce detection of RSV antigen by 50% compared with untreated virus-infected cells. Palivizumab exhibited median EC50 values of 0.65 μg/ml (mean [standard deviation] = 0.75 [0.53] μg/ml; n=69, range 0.07–2.89 μg/ml) and 0.28 μg/ml (mean [standard deviation] = 0.35 [0.23] μg/ml; n=35, range 0.03–0.88 μg/ml) against clinical RSV A and RSV B isolates, respectively. The majority of clinical RSV isolates tested (n=96) were collected from subjects in the United States.
Palivizumab binds a highly conserved region on the extracellular domain of mature RSV F protein, referred to as antigenic site II or A antigenic site, which encompasses amino acids 262 to 275. In a genotypic analysis of 126 clinical isolates from 123 children who failed immunoprophylaxis, all RSV mutants that exhibited resistance to palivizumab (n=8) were shown to contain amino acid changes in this region of the F protein. No polymorphic or non-polymorphic sequence variations outside of the A antigenic site on the RSV F protein were shown to render RSV resistant to neutralisation by palivizumab. At least one of the palivizumab resistance-associated substitutions, N262D, K272E/Q, or S275F/L was identified in these 8 clinical RSV isolates resulting in a combined resistance-associated mutation frequency of 6.3% in these patients. A review of clinical findings did not reveal an association between A antigenic site sequence changes and RSV disease severity among children receiving palivizumab immunoprophylaxis who develop RSV lower respiratory tract disease. Analysis of 254 clinical RSV isolates collected from immunoprophylaxis-naïve subjects revealed palivizumab resistance-associated substitutions in 2 (1 with N262D and 1 with S275F), resulting in a resistance associated mutation frequency of 0.79%.
Antibody to palivizumab was observed in approximately 1% of patients in the IMpact-RSV during the first course of therapy. This was transient, low titre, resolved despite continued use (first and second season), and could not be detected in 55 of 56 infants during the second season (including 2 with titres during the first season). Immunogenicity was not studied in the congenital heart disease study. Antibody to palivizumab was evaluated in four additional studies in 4337 patients (children born at 35 weeks of gestation or less and 6 months of age or less, or 24 months of age or less with bronchopulmonary dysplasia, or with haemodynamically significant congenital heart disease were included in these studies) and was observed in 0%–1.5% of patients at different study timepoints. There was no association observed between the presence of antibody and adverse events. Therefore, anti-drug antibody (ADA) responses appear to be of no clinical relevance.
In a placebo-controlled trial of RSV disease prophylaxis in (IMpact-RSV trial) 1502 high-risk children (1002 Synagis; 500 placebo), 5 monthly doses of 15 mg/kg reduced the incidence of RSV related hospitalisation by 55% (p=<0.001). The RSV hospitalisation rate was 10.6% in the placebo group. On this basis, the absolute risk reduction is 5.8% which means the number needed to treat is 17 to prevent one hospitalisation. The severity of RSV disease in children hospitalised despite prophylaxis with palivizumab in terms of days in ICU stay per 100 children and days of mechanical ventilation per 100 children was not affected.
A total of 222 children were enrolled in two separate studies to examine the safety of palivizumab when it is administered for a second RSV season. One hundred and three (103) children received monthly palivizumab injections for the first time, and 119 children received palivizumab for two consecutive seasons. No difference between groups regarding immunogenicity was observed in either study. However, as the efficacy of palivizumab when administered to patients as a second course of treatment during an ensuing RSV season has not been formally investigated in a study performed with this objective, the relevance of these data in terms of efficacy is unknown.
In an open label prospective trial designed to evaluate pharmacokinetics, safety, and immunogenicity after administration of 7 doses of palivizumab within a single RSV season, pharmacokinetic data indicated that adequate mean palivizumab levels were achieved in all 18 children enrolled. Transient, low levels of antipalivizumab antibody were observed in one child after the second dose of palivizumab that dropped to undetectable levels at the fifth and seventh dose.
In a placebo-controlled trial in 1,287 patients 24 months of age with haemodynamically significant congenital heart disease (639 Synagis; 648 placebo), 5 monthly doses of 15 mg/kg Synagis; reduced the incidence of RSV hospitalisations by 45% (p=0.003) (congenital heart disease study). Groups were equally balanced between cyanotic and acyanotic patients. The RSV hospitalisation rate was 9.7% in the placebo group and 5.3% in the Synagis group. Secondary efficacy endpoints showed significant reductions in the Synagis group compared to placebo in total days of RSV hospitalisation (56% reduction, p=0.003) and total RSV days with increased supplemental oxygen (73% reduction, p=0.014) per 100 children.
A retrospective observational study was conducted in young children with hemodynamically significant congenital heart disease (HSCHD) comparing the occurrence of primary serious adverse events (PSAEs: infection, arrhythmia, and death) between those who did (1009) and did not receive Synagis prophylaxis (1009) matched by age, type of cardiac lesion, and prior corrective surgery. The incidence of arrhythmia and death PSAEs was similar in children who did and did not receive prophylaxis. The incidence of infection PSAEs was lower in children who received prophylaxis as compared to those children who did not receive prophylaxis. The results of the study indicate no increased risk of serious infection, serious arrhythmia, or death in children with HSCHD associated with Synagis prophylaxis compared with children who did not receive prophylaxis.
Two clinical studies were conducted to directly compare liquid and lyophilised formulations of palivizumab. In the first study, all 153 premature infants received both formulations in different sequences. In the second study, 211 and 202 premature infants or children with chronic lung disease received liquid and lyophilised palivizumab, respectively. In two additional studies, liquid palivizumab was used as an active control (3918 pediatric subjects) to evaluate an investigational monoclonal antibody for prophylaxis of serious RSV disease in premature infants or children with BPD or hemodynamically significant CHD (see below for further details of these two studies). The overall rate and pattern of adverse events, study drug discontinuation due to AEs, and the number of deaths reported in these clinical studies were consistent with those observed during the clinical development programs for the lyophilised formulation. No deaths were considered related to palivizumab and no new ADRs were identified in these studies.
This trial, conducted at 347 centers in the North America, European Union and 10 other countries, studied patients less than or equal to 24 months of age with CLDP and patients with premature birth (less than or equal to 35 weeks gestation) who were less than or equal to 6 months of age at study entry. Patients with hemodynamically significant congenital heart disease were excluded from enrollment in this study and were studied in a separate study. In this trial, patients were randomized to receive 5 monthly injections of 15mg/kg of liquid palivizumab (N=3306) used as active control for an investigational monoclonal antibody (N=3329). Subjects were followed for safety and efficacy for 150 days. Ninetyeight percent of all subjects receiving palivizumab completed the study and 97% received all five injections. The primary endpoint was the incidence of RSV hospitalisation. RSV hospitalisations occurred among 62 of 3306 (1.9%) patients in the palivizumab group. The RSV hospitalisation rate observed in patients enrolled with a diagnosis of CLDP was 28/723 (3.9%) and in patients enrolled with a diagnosis of prematurity without CLDP was 34/2583 (1.3%).
This trial, conducted at 162 centers in North America, European Union and 4 other countries over two RSV seasons, studied patients less than or equal to 24 months of age with hemodynamically significant CHD. In this trial, patients were randomized to receive 5 monthly injections of 15mg/kg of liquid palivizumab (N=612) used as active control for an investigational monoclonal antibody (N=624). Subjects were stratified by cardiac lesion (cyanotic vs. other) and were followed for safety and efficacy for 150 days. Ninety-seven percent of all subjects receiving palivizumab completed the study and 95% received all five injections. The primary endpoint was a summary of adverse events and serious adverse events, and the secondary endpoint was the incidence of RSV hospitalisation. The incidence of RSV hospitalisation was 16 of 612 (2.6%) in the palivizumab group.
In studies in adult volunteers, palivizumab had a pharmacokinetic profile similar to a human IgG1 antibody with regard to volume of distribution (mean 57 ml/kg) and half-life (mean 18 days). In prophylactic studies in premature and bronchopulmonary dysplasia paediatric populations, the mean half-life of palivizumab was 20 days and monthly intramuscular doses of 15 mg/kg achieved mean 30 day trough serum active substance concentrations of approximately 40 μg/ml after the first injection, approximately 60 μg/ml after the second injection, approximately 70 μg/ml after the third injection and fourth injection. In the congenital heart disease study, monthly intramuscular doses of 15 mg/kg achieved mean 30 day trough serum active substance concentrations of approximately 55 µg/ml after the first injection and approximately 90 µg/ml after the fourth injection.
Among 139 children in the congenital heart disease study receiving palivizumab who had cardio-pulmonary bypass and for whom paired serum samples were available, the mean serum palivizumab concentration was approximately 100 μg/ml pre-cardiac bypass and declined to approximately 40 g/ml after bypass.
The pharmacokinetics and safety of palivizumab liquid formulation and palivizumab lyophilised formulation, following 15 mg/kg intramuscular administration, were compared in a cross-over trial of 153 infants less than or equal to 6 months of age with a history of prematurity (less than or equal to 35 weeks gestational age). The results of this trial indicated that the trough serum concentrations of palivizumab were similar between the liquid formulation and the lyophilised formulation and bioequivalence of the liquid and the lyophilised formulation was demonstrated.
Single dose toxicology studies have been conducted in cynomolgus monkeys (maximum dose 30 mg/kg), rabbits (maximum dose 50 mg/kg) and rats (maximum dose 840 mg/kg). No significant findings were observed.
Studies carried out in rodents gave no indication of enhancement of RSV replication, or RSV-induced pathology or generation of virus escape mutants in the presence of palivizumab under the chosen experimental conditions.
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