Fill the pipeline. In three words, that’s the reason behind Idec Pharmaceuticals’ stunning decision to merge with Biogen Inc. of Cambridge, Mass. The deal, which moves the headquarters to Cambridge, is expected to close later this year.

Now that Idec is building a huge manufacturing plant in Oceanside and expanding in UTC, the company faces relentless pressure to keep cranking out the hits, like its blockbuster cancer drug, Rituxan.

Construction in Oceanside will continue as planned. Moreover, the merger will make it more likely the plant, the first phase of which is scheduled to be completed by the end of 2005, will be kept busy.

Although Idec is developing more products, biotech companies have a high failure rate in bringing products to market. The only defense they have is to pursue many drug candidates, hoping that some will navigate the regulatory maze and get on the market.

Biogen helps with its own research capacity, focused on immunology. This meshes nicely with Idec’s strength in cancer research. Rituxan made Idec a major biotech company. But most of the money goes to Idec’s partner, Genentech, which provided cash and manufacturing capacity when Idec had neither.

The new company, to be named Biogen Idec, will keep its employees in San Diego, and add Biogen’s research capacity. But even that may not be enough, given the vagaries of biotech drug testing.

So Biogen Idec will be looking to acquire promising drugs from biotech companies, Idec chief executive William H. Rastetter said during a conference call announcing the merger. Rastetter notes the merged company will have the financial clout to do so, with an annual research and development budget of about $550 million.

In other words, Biogen Idec, the third largest biotech company (behind Genentech and Amgen) will be a cash-rich big biotech brother to smaller fry with big ideas but small budgets — just like Idec was when it struck its deal with Genentech. And just like Genetech, the decision makers will work somewhere else.

— Bradley J. Fikes