Background: Respiratory syncytial virus (RSV) is the leading cause of lower respiratory disease in infants and children. MEDI-493 (palivizumab, Synagis) is a humanized monoclonal IgG1 antibody to the fusion protein of RSV, and it is highly active in vitro against RSV A and B strains.
Objective: To describe the safety, tolerance, immunogenicity and pharmacokinetics of monthly intramuscular injections of MEDI-493 among premature infants and children with bronchopulmonary dysplasia and to compare these data with information previously obtained with intravenous dosing.
Design: A Phase I/II multicenter, open label, escalating dose clinical trial. PATIENT POPULATION AND DOSING REGIMEN: Children (n=65) born prematurely at < or =35 weeks of gestation who were < or =6 months of age (n=41) and children with bronchopulmonary dysplasia who were < or =24 months of age (n=24) were enrolled. From 1 to 5 monthly injections were given at doses of 5 mg/kg (n=11), 10 mg/kg (n=6) and 15 mg/kg (n=48). Serum was collected before administration of each dose, 30 days after the last dose, and 2, 7 and 14 days after the first and second doses for measurement of MEDI-493 concentrations by enzyme-linked immunosorbent assay.
Results: The pharmacokinetics of MEDI-493 were similar to those of other human IgG1 antibodies. Mean serum MEDI-493 concentrations were 91.1 microg/ml (range, 52.3 to 174.0) 2 days after the initial dose of 15 mg/kg and 49.2 microg/ml (range, 13.5 to 132.0) at 30 days. Monthly dosing of 15 mg/kg maintained mean trough concentrations of approximately 70 microg/ml. These concentrations were similar to previously published trough concentrations after i.v. administration. MEDI-493 injections were well-tolerated. Only three children had adverse events judged to be possibly related to MEDI-493. Ten children had transient, low titer anti-MEDI-493 binding titers (1:10 to 1:40) which were not associated with a pattern of specific adverse events or alterations of MEDI-493 concentrations. Two patients in the 5-mg/kg dose group were hospitalized for RSV; no RSV hospitalizations were found in the higher dose groups.
Conclusions: MEDI-493 was safe and well-tolerated. Monthly intramuscular doses of 15 mg/kg maintained mean trough serum concentrations that were above 40 microg/ml (the value associated with 99% reduction of pulmonary RSV in the cotton rat model). These concentrations were similar to those previously reported with i.v. administration of MEDI-493.