MedImmune is feeling on the up after announcing positive results from the second year of treatment with motavizumab (MEDI-524) - a new monoclonal antibody specifically designed to treat respiratory syncytial virus - at the Infectious Diseases Society of America Annual Meeting in San Diego last weekend.

MedImmune derived motavizumab from Synagis (palivizumab), another RSV-specific MAb already recommended for children at high-risk of developing serious RSV disease, such as certain preterm infants or some young children with congenital heart disease. MedImmune say that motavizumab offers enhanced potency compared with palivizumab and is currently preparing the US regulatory submission.

The Phase I/II, randomized, double-blind study enrolled 136 preterm infants at high risk of the disease who were aged less than 24 months and who received at least three motavizumab doses in their first RSV season. The children received monthly motavizumab or palivizumab injections during their second RSV season.

Motavizumab’s safety profile during the second season was consistent with that during the first year and comparable with palivizumab: 84.8% and 88.6% of the children developed adverse events respectively. Injection site erythema was the most common drug-related adverse event with motavizumab and palivizumab (15.2% and 11.4% respectively). The erythema was transient, lasting between one and two days, mild and did not require additional treatment. One child developed a transient acute skin hypersensitivity reaction after the third dose of motavizumab. Adverse events considered to be treatment related occured in 18.2% and 17.1% of the motavizumab and palivizumab groups respectively. Serious adverse events occurred in 6.1% of the motavizumab group during the second season compared with 1.4% in the palivizumab arm.

Motavizumab serum trough concentrations during the second season increased during dosing and were comparable with those in the first season. No evidence of anti-palivizumab immune reactivity emerged during the second season. “It appears that motavizumab or palivizumab can safely be administered for a second sequential RSV season in high-risk patients who received motavizumab during their first RSV season,” the authors concluded.

Respiratory syncytial virus, the commonest lower respiratory tract infection, causes bronchiolitis in infants and young children, acute bronchitis in older children and is the leading cause of hospitalisation among children less than one year of age.

Synagis is one of MedImmune's strongest selling drugs. In the first quarter of this year, the firm's revenues rose 15.4% to $574.8 million, driven by a strong increase in sales of Synagis, its paediatric vaccine for respiratory syncytial virus, up 9% to $507 million. MedImmune is in the process of being acquired by AstraZeneca, which itself has a strong presence in the respiratory field.