Pfizer Inc. said on Tuesday that it plans by mid-August to ask regulators to approve an initial public offering of up to a 20 percent stake in the new animal health business, to be called Zoetis. Pfizer's animal health unit, with $4.2 billion in revenue last year, has more than 9,000 employees and sells medicines, vaccines and other products for livestock and pets.

"If the IPO is successfully completed, which we are targeting for the first half of 2013, we will have a variety of options to achieve a full separation of Zoetis," Pfizer Chief Executive Ian Read said in a release, adding that he wants to maximize after-tax returns to shareholders.

Shares of Pfizer have jumped more than 23 percent in the past year, in large part because of the company's plan to divest its animal health units and infant formula business and return much of the proceeds to shareholders through share buybacks and hefty dividends.

Pfizer earned $3.25 billion, or 43 cents per share, in the second quarter, up from $2.61 billion, or 33 cents per share, a year earlier.

Sales of Lipitor, which lost patent protection in November, fell 53 percent to $1.22 billion in the quarter.

Pfizer shares rose 1.4 percent in premarket trading to $24.05.

Read more about Pfizer Animal Health here.