The U.S. Federal Trade Commission on Wednesday cleared Pfizer Inc.'s (PFE) $68 billion deal to acquire rival Wyeth (WYE), but required the companies to divest assets in the animal-health market as a condition of government approval.

With the FTC's clearance, Pfizer said it expects to close the transaction on Thursday.

The FTC said the divestitures will protect competition in the market for animal vaccines and other animal health products.

The commission found no competitive concerns about the merger's effect on human-health products, saying the deal likely wouldn't harm consumers in any prescription drug market. The FTC said the two companies' product portfolios were highly complementary.

The Pfizer-Wyeth deal, announced in January, received approval from the European Commission in July.

Jeffrey Kindler, Pfizer's chairman and chief executive, said in a statement that the company was pleased to have received all the necessary regulatory approvals and looked forward to combining the two companies.

The FTC said Wednesday that it devoted extensive resources to investigating the merger. Notably, the commission published a five-page statement explaining how it evaluated the deal, saying the framework would guide the commission's approach to future drug-company mergers.

"Although the commission, based on the evidence gathered, determined that this transaction did not raise anticompetitive concerns in the markets for human pharmaceuticals, the commission remains dedicated to ensuring that pharmaceutical markets are competitive," the FTC said.

In addition to examining Pfizer and Wyeth's overlapping products, the commission said it took a big-picture approach that looked at whether the merger would harm competition broadly, including whether it would decrease drug research generally or slow the pace of innovation.

"The evidence demonstrates that it will not," the FTC said.

On the issue of overlaps, the commission said it paid particular attention to the companies' treatments for Alzheimer's disease. Pfizer markets the leading Alzheimer's drug Aricept, while Wyeth has several products in development. The FTC said it concluded the overlap was not a threat to competition in that market.

As part of its settlement with the FTC, Pfizer has agreed to sell half of Wyeth's Fort Dodge U.S. animal-health business to Boehringer Ingelheim Vetmedica, Inc., within 10 days of the acquisition.

Pfizer and Wyeth announced the animal-health agreement with Boehringer Ingelheim last month.

Assets to be sold include vaccines for cattle, dogs and cats.

New York-based Pfizer already was the world's largest prescription pharmaceutical company, with $48.3 billion in revenue for 2008. Wyeth, based in Madison, N.J., totaled $23 billion in revenue last year.

In a somewhat unusual scenario, only two of the four FTC commissioners participated in the vote to clear the merger. Commissioners William Kovacic and Pamela Jones Harbour were recused. An FTC spokesman said commissioners do not provide explanations for their recusals.

-By Brent Kendall, Dow Jones Newswires; 202-862-9222; brent.kendall@dowjones.com

(Peter Loftus contributed to this article.)