In an effort to better focus on its core businesses, Merck will sell back rights to Kuvan, a drug used to treat a rare metabolic disorder, to BioMarin Pharmaceutical, for up to $586 million.

The deal also includes Merck returning the option to develop Peg-Pal, also designed to treat the metabolic disorder known as PKU, to California-based BioMarin. In 2005, Merck acquired the exclusive rights to Kuvan and the option to develop Peg-Pal in markets outside of the U.S. and Japan from BioMarin.

"Returning the rights of Kuvan and Peg-Pal to BioMarin will allow Merck to fully focus on its core businesses, as well as further align R&D investment behind key strategic areas," said Merck Healthcare CEO Belén Garijo in a statement to The Street.

Read The Street release