By Ransdell Pierson

NEW YORK (Reuters) - The chief financial officer of Pfizer Inc (PFE.N: Quote, Profile, Research) on Tuesday said the company does not feel obliged to buy mid-size drugmakers, in the $10 billion to $15 billion price range, before its Lipitor cholesterol drug loses U.S. patent protection by 2012.

"We don't think we have to do them," Frank D'Amelio said in an interview when asked about assertions by some industry analysts that Pfizer needs to make deals of that size in order to obtain new medicines to offset expected lower sales of Lipitor.

"If they make good sense, we'll consider and possibly do them, but not 'have to' or 'need to,"' D'Amelio said.

Pfizer in recent years has focused on far smaller transactions, typically licensing deals for individual products made by biotechnology companies that are not yet approved for sale.

Many industry analysts have urged Pfizer to instead go after bigger prey, including companies like Biogen Idec (BIIB.O: Quote, Profile, Research) that already have big-selling products on the market.

"Last year we did a series of smaller deals; this year we've done some smaller deals," D'Amelio said, adding that Pfizer would continue to be "very prudent" about future transactions.

Pfizer has said it is not interested, however, in any "mega-deals" -- meaning purchases of the largest U.S. and European drugmakers -- because of inherent problems of companies that size.

Pfizer itself became the world's biggest drugmaker with two earlier mega-mergers. It paid $114 billion in 2000 for its longtime partner Warner-Lambert Corp, thereby gaining full ownership of Lipitor, and spent $60 billion in 2003 for Pharmacia Corp.