ALLERGAN, Mich. — Perrigo Co. is acquiring Elan Corp., an Irish pharmaceutical firm, for $8.6 billion in a transaction that should give the manufacturer of over-the-counter drugs a low tax base for international ­expansion.

Purchasing Dublin-based Elan enables Perrigo to redomicile itself in Ireland, where the corporate income tax rate is 12.5% and gives Perrigo access to royalties for the multiple sclerosis drug Tysabri, which Elan discovered and then sold to Biogen Idec Inc. in February.

"Through this transaction, Perrigo establishes a diversified platform for further international expansion," chairman and chief executive officer Joseph Papa said in a statement.

Perrigo sells nonprescription products for such conditions as acid indigestion and nasal congestion, as well as generic drugs, nutritional supplements and diabetes products. The acquisition will result in more than $150 million of recurring after-tax annual operating expense and tax savings, the company said.

The combined company will list shares on the New York Stock Exchange and the Tel Aviv Stock Exchange. Perrigo shares are traded in Israel because in 2005 the company acquired Israeli generic drug maker Agis Industries Ltd.

Perrigo would also gain access to more than $2 billion in tax deductions, almost all in Ireland, chief financial officer Nigel Clerkin said during a conference call.

Allergan Inc., Mylan Inc. and Forest Laboratories Inc. were among other drug makers that reportedly considered a purchase of Elan.