Botox-maker Allergan is buying MAP Pharmaceuticals, its partner in developing the orally-inhaled migraine drug Levadex, in a nearly $1 billion bid to expand the portfolio of products it can sell to neurologists and pain specialists.

The $958 million purchase comes as the companies await an anticipated April U.S. Food and Drug Administration decision on whether to approve Levadex. In March 2012, the FDA issued a complete response letter seeking additional information from MAP regarding issues relating to chemistry, manufacturing, and controls. With the drug resubmitted for review, Allergan and MAP are hoping that an approval will unlock access to an underserved multi-billion dollar migraine treatment market.

“One of the key drivers of Allergan’s continued success is our focus on medical specialties where we have extensive knowledge of physician and patient needs, and can provide a broad portfolio of products,” says David Pyott, Allergan’s president and CEO.

Allergan’s per share cash offer price represents a 60 percent premium over MAP’s closing stock price of $15.58 on January 22, before the deal was announced.

After gaining approval to sell Botox injections for the treatment of migraines in 2010, Allergan inked an agreement with MAP in January 2011 to co-promote the inhalable Levadex, contingent upon potential regulatory approvals in the United States and Canada. Under terms of that collaboration, Allergan agreed to pay MAP $60 million upfront and as much as $97 million in milestones. The companies had also agreed to share profits from sales to U.S. neurologists and pain specialists.

Should Levadex secure approval and the transaction close as planned in the first or second quarter of 2013, Allergan anticipates the transaction will be dilutive to 2013 earnings per share by approximately 7 cents and accretive to earnings per share by the second half of 2014.