Background:

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection in young children. Motavizumab is an investigational humanized monoclonal antibody for RSV prophylaxis.

Methods:

A dose-escalation study was conducted followed by assessment of safety, tolerability, serum concentrations, and immunogenicity during a second consecutive RSV season. In season 1, premature infants aged≤ 6 months or children≤ 24 months with chronic lung disease of prematurity received monthly motavizumab (3 or 15 mg/kg). In season 2, children who received≥ 3 motavizumab doses in season 1 were randomized to receive monthly motavizumab or palivizumab 15 mg/kg.

Results:

Of 217 children enrolled in season 1, 211 (97.2%) received motavizumab 15 mg/kg and 205 (94.5%) patients completed the study through 90 days after the final dose. In season 2, 136 children were randomized to receive motavizumab (n= 66) or palivizumab (n= 70). The most commonly reported related adverse event was transient injection site erythema. In season 1, mean trough motavizumab concentrations were 7.9 and 50.2 μg/mL after the 3-and 15-mg/kg doses, respectively. Trough concentrations increased with repeated motavizumab dosing; a similar pattern was seen in season 2. Antimotavizumab reactivity occurred infrequently (3.3%) in season 1. In season 2, no treatment group–specific antidrug antibody was detected through 90 to 120 days after dosing with either product.

Conclusions:

The pharmacokinetic profile of motavizumab was similar to that of other IgG 1 antibodies. Increased adverse reactions or immunogenicity were not observed during and after a second season of treatment with motavizumab. Safety findings from these studies supported the continued development of motavizumab.