MedImmune Inc. of Gaithersburg said yesterday that it will take over full responsibility for selling its blockbuster drug Synagis in the United States in 2006, ending a seven-year-long deal with pharmaceutical firm Abbott Laboratories.

Analysts said getting out of the deal with Abbott would ultimately cost MedImmune about $350 million, but the firm will benefit by avoiding yearly commission payments that had reached $200 million. Annual sales of Synagis, which prevents certain respiratory infections in babies, are about $1 billion worldwide.

The company said it will boost its pediatric sales staff by 125 representatives, to 425, to market Synagis.

In ending the deal, analysts and MedImmune executives say the firm significantly reduced the risks of experiencing two uncomfortable situations -- having to compete against Abbott if a second-generation version of Synagis is launched in 2008, and not meeting future earnings goals because of the commission payments it was making to its partner.

"Wall Street hates risk and this deal allows them to reduce some," said Alexander Hittle, an analyst with A.G. Edwards & Sons Inc. "This is a good deal for them. We like it."

MedImmune shares closed yesterday up $2.83, or 10 percent, at $29.93.

While Abbott has helped sell Synagis since its launch in 1998, MedImmune hopes to sell a new version, called Numax, on its own if the drug wins approval in 2007 or 2008.

Because Abbott receives commissions based on the amount of Synagis sold, there could have been tension between the two companies, with MedImmune pushing the newer, more expensive version. Instead of that potential clash, "now we control both products," said MedImmune chief executive David M. Mott. At the same time, there was some concern about the company's bottom line should Numax not win approval. If they had to continue co-selling Synagis, while dishing out costly commission payments, executives worried about the prospects of reaching their profit goals over the next few years.

MedImmune officials said they expect the deal will cut into the company's earnings by about 10 or 11 cents per share for 2005 and 2006. However, by 2007 MedImmune expects benefits of 28 cents per share, and it raised its earnings-per-share target to $1.15. The average analyst estimate was 70 cents a share, according to Thomson First Call.

The firm recently reported a second-quarter loss of $44.2 million (18 cents a share) on $88.5 million in revenue, compared with a $100.3 million loss (40 cents) on $93.6 million in revenue in the corresponding year-ago period.

Mott told analysts that the increase in sales force was strategically important given the firm's hopes to launch a new version of its nasal flu vaccine FluMist in 2007. The company hopes regulators will expand approval to children under age 5. Currently, the vaccine is only approved for those ages 5 to 49.

Earlier this week, the company completed a deal with GlaxoSmithKline PLC to buy the rights to develop a drug that prevents bloodstream infections in premature babies.