By Chelsey Dulaney 

Allergan PLC said Tuesday that it has reached a deal to buy the exclusive world-wide rights to two of Merck & Co.'s experimental migraine drugs for an upfront payment of $250 million.

Merck could also receive milestone and royalty payments based on commercialization of the two calcitonin gene-related peptide (CGRP) receptor antagonists, which are being developed for treatment and prevention of migraines.

CGRP has been a key focus in the hunt for new migraine treatments in recent years. CGRP is a brain chemical that appears to play a role in the transmission of pain, but not in other brain functions, such as cognition or mood. Researchers have been trying a variety of experimental drugs to stop CGRP from working by blocking its receptors in the brain.

In 2011, Merck called off a CGRP development program after patients showed evidence of liver toxicity. The companies noted Tuesday that the two new drugs haven't shown evidence of toxicity in clinical trials to date.

Dublin-based Allergan expects to begin a phase 3 study for one of the oral drugs in 2016, while the company expects to begin a phase 2 study for the other next year.

Allergan will pay out $125 million after it receives regulatory clearance and $125 million next April.

Allergan has been bulking up its portfolio through a string of deals recently.

On Monday, Allergan said it struck a deal to buy Oculeve, a maker of experimental dry-eye disease treatments, for an upfront payment of $125 million in cash.

That follows the Botox maker's deal last month to buy Kythera Biopharmaceuticals Inc. and its newly approved double-chin treatment in a $2.1 billion deal that aims to plump up its lineup of cosmetic medicines.

For its part, Merck said the deal allows it to focus its resources on its therapeutic areas.

Write to Chelsey Dulaney at Chelsey.Dulaney@wsj.com

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