The maker of the world’s best-selling Alzheimer’s medicine is going after MGI in order to gain more cancer drugs, and is the latest example of what larger drugmakers are willing to do when faced with thinning pipelines. MGI investors will get $41 a share, which amounts to a 23 percent premium above MGI’s closing price on Friday,

The Aricept Alzheimer’s drug is Eisai’s biggest seller, but revenue is expected to drop in 2010 when cheaper generics become available. Eisai shares plunged to a two-month low in October because of delays in potential successors, Bloomberg News notes. “This acquisition will also help us achieve our sales target of 1 trillion yen by 2012,” Eisai’s ceo, Haruo Naito, told reporters and analysts in a briefing in Tokyo. MGI, which is based in Bloomington, Minnesota, sells Aloxi shots for chemotherapy- induced nausea.

“Large drugmakers need to expand the product selections in their pipelines as they face patent expiry,” Shinsuke Nagasaki at Mizuho Asset Management tells Bloomberg. “There is a higher possibility that we’ll see more mergers.” Eisai is paying about 9.7 times MGI’s revenue. AstraZeneca paid about 10.8 times MedImmune’s sales when it bought the biotech for $15.2 billion in April, Bloomberg notes.

MGI said on Nov. 29 that it hired Lehman Brothers Holdings to explore a possible sale of the company. At least two analysts cut their ratings on MGI Pharma last month on concerns about revenue growth, Bloomberg adds.

Sales of Aloxi, the company’s biggest drug, fell 5.8 percent in the third quarter to $66.3 million. The second-biggest product, Dacogen for bone-marrow disease, may also face increased competition after a rival drugmaker was purchased by Celgene, analysts said. Eisai bought Morphotek Inc. for $325 million to gain potential new treatments for cancer in April this year. It also bought exclusive rights to four cancer-related treatments from Ligand Pharmaceutical for $205 billion to help establish the company’s global oncology business in October last year.