London - AstraZeneca of Britain said Wednesday that it had agreed to pay up to $2.1 billion for a slate of respiratory drugs from the Spanish drugmaker Almirall.

The company, which fended off a takeover push from Pfizer in May, said it would initially pay $875 million to Almirall for the rights to the drugs, and up to about $1.2 billion more if development and sales milestones are met.

The acquisition would bolster AstraZeneca's existing respiratory business, a crucial growth area for the company.

"Chronic respiratory disease affects hundreds of millions of people around the world," Pascal Soriot, AstraZeneca's chief executive, said in a statement Wednesday. "By combining our innovative portfolios and leveraging AstraZeneca's global scientific and commercial capabilities, we will strengthen our ability to address the entire spectrum of care in asthma and COPD," he added, referring to chronic obstructive pulmonary disease.

Under the agreement, AstraZeneca will own the development and commercialization rights to Almirall's existing respiratory business, including Eklira, a treatment for chronic obstructive pulmonary disease.

The transaction, which is subject to regulatory approval, is expected to be completed by the end of 2014. The companies said they expected "a significant number of employees" in Almirall's respiratory business to transfer to AstraZeneca after the completion of the deal.

AstraZeneca plans to finance the transaction through existing cash and debt.