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Dec 2 (Reuters) - Japanese drugmaker Otsuka Holdings Co Ltd plans to buy U.S.-based Avanir Pharmaceuticals Inc for about $3.5 billion to expand its neurologic drug portfolio ahead of an expiration of a key drug patent.
Otsuka said subsidiary Otsuka Pharmaceutical Co Ltd would pay $17 per share in cash, or a premium of 13.3 percent to Avanir's closing price on Monday.
The deal, Otsuka's biggest according to Thomson Reuters data, comes as the company aims to beef up its product pipeline ahead of a so-called "patent cliff" after April 2015, when its U.S. patent for schizophrenia drug Abilify expires and opens the way to generic competition.
Its global sales of Abilify totaled 575.7 billion yen ($5 billion) in the last fiscal year, around 40 percent of the total for Otsuka Holdings. The United States is the biggest market for the drug.
Japanese companies, helped by cash-rich balance sheets and encouraged by an ageing domestic population, are looking overseas for growth.
Otsuka will launch a tender offer within 10 business days to purchase all outstanding shares of Avanir, the companies said. The deal is expected to close in the first quarter of 2015.
Otsuka Pharmaceutical President Taro Iwamoto said the deal would "bring together Otsuka's experience and business track record in the area of mental illnesses with Avanir's strengths in neurologic diseases", according to a statement.
Avanir developed Nuedexta, which treats pseudobulbar affect, a neurological disorder characterised by involuntary outbursts of crying or laughter.
But it failed to win approval from the U.S. Food and Drug Administration for a migraine drug device in November, a few weeks after the regulator had raised questions regarding some data submitted as part of the marketing application.
After the deal, Avanir will operate as a unit of Otsuka America Inc and will partner with Otsuka to enhance its development and marketing efforts in central nervous system-related disorders.
Goldman Sachs advised Otsuka, while Centerview Partners advised Avanir. (1 US dollar = 118.8800 Japanese yen)
Reporting by Ritsuko Ando in Tokyo and Neha Dimri in Bengaluru; Editing by Gopakumar Warrier and Jane Baird