MEDI-493 is 50-100 times more potent than RSV immune globulin in the cotton rat model of RSV prophylaxis. A randomized (2:1) double-blind, placebo-controlled trial (IMpact-RSV) was conducted to determine the efficacy and safety of MEDI-493 prophylaxis in premature infants with and without BPD. Between 11/15/96 and 12/13/96, 1502 children were randomized at 139 centers in the US, Canada and the UK. Children received 15 mg/kg MEDI-493 IM monthly or placebo during the RSV season. Characteristics of groups were balanced at entry; 99% completed the protocol, 93% received all 5 injections. MEDI-493 prophylaxis was associated with a 55% reduction in RSV hospitalization(p<0.001). The direction of the effect was consistent across countries, through the respiratory season, and in subgroups by gender, age, weight, and infants with BPD (39% reduction, p=0.038) and without BPD (78% reduction, p<0.001). No significant differences were found in study drug related adverse events (AEs), 10.0% placebo, 10.9% MEDI-493; related hepatic and renal AEs were reported in 1% of each group. Site of injection reactions were uncommon (1.8% placebo vs 2.7% MEDI-493); permanent discontinuation of study drug due to a related AE was rare (0.3%). Fatalities were balanced: 1.0% placebo, 0.4% MEDI-493. In conclusion, MEDI-493 was safe and effective for the prevention of serious RSV disease in high-risk children with BPD and/or a history of prematurity. Table

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