Pfizer Inc. reportedly will acquire King Pharmaceuticals Inc. and King’s Alpharma Animal Health.

It is a $3.6 billion deal meant to shore up the portfolio of the world's largest drug company, it includes both human-health and animal-health products.

The deal to buy King Pharmaceuticals Inc. is Pfizer's largest since it bought rival Wyeth for $68 billion in 2009. Pfizer already has a large stake in the pain drug market with its drugs Lyrica and Celebrex, which combined for more than $5 billion in sales in 2009. But now the company is betting that King's work on "abuse-resistant" pain drugs will pay off and help make up for the revenue it will lose when top sellers such as the cholesterol drug Lipitor no longer have patent protection in a few years.

King markets one such drug, called Embeda, and it's seeking approval for two others under the names Remoxy and Acurox. Remoxy is similar to Purdue Pharma LP's OxyContin, the top-selling painkiller in the U.S. Both are designed to treat pain by slowly releasing the narcotic oxycodone. 

(Parts of this report were contributed by The Associated Press)