Pfizer Inc is in talks to merge its off-patent drugs business with Mylan NV in a stock deal, according to a source familiar with the matter.

Mylan shareholders would receive a little more than 40% of the newly formed entity, with Pfizer shareholders receiving the remainder, the person said, adding that Pfizer would also get about $12 billion in proceeds from a new sale of debt.

Separation of Pfizer's off-patent business would be a tax-free spin-off, the person added.

Last year, Pfizer said it was planning to reorganize into three units, separating its consumer healthcare business.

The restructuring will allow the company to evaluate its businesses better and could result in selling or spinning off its off-patent drugs, Wall Street analysts earlier said.

The Wall Street Journal first reported about the talks between the companies on Saturday.

Pfizer and Mylan did not immediately respond to requests for comment.