Jan. 30 (Bloomberg) -- Pfizer Inc. agreed to pay $4.5 billion if banks decide against lending the world’s biggest drugmaker enough to complete its $68 billion purchase of Wyeth.

JPMorgan Chase & Co., Bank of America Corp., Barclays Plc, Citigroup Inc., and Goldman Sachs Group Inc. assembled Pfizer’s $22.5 billion loan package. The drugmaker must pay Wyeth the $4.5 billion breakup fee if the lenders pull out of the deal. The lenders may act if Pfizer’s operations decline a significant amount or if the company’s credit rating falls below A2, the sixth-highest ranking, as determined by Moody’s Investors Services. It is now Aa1, the second-highest rating.

Pfizer, the world’s largest drugmaker, announced the Wyeth purchase on Jan. 26. Pfizer gains the depression pill Effexor and pneumonia vaccine Prevnar to offset some of the $12 billion in sales it begins losing in 2011 when Lipitor, which generates a quarter of the company’s revenue, gets generic competition.

Pfizer said its 364-day bridge loan will cost 3 percentage points over the London interbank offered rate, with pricing increasing 0.5 percentage points each quarter, according to a regulatory filing. The companies also disclosed the breakup fee in yesterday’s filings.

Wyeth, of Madison, New Jersey, is on the hook for $2 billion if it drops the deal to accept a higher offer from another bidder, the company said. Wyeth also will get to appoint two members of the Pfizer board of directors.

To contact the reporter on this story: Shannon Pettypiece in New York at spettypiece@bloomberg.net

Last Updated: January 30, 2009 00:01 EST