Jazz Pharmaceuticals PLC will acquire Eusa Pharma Inc., which has its U.S. headquarters in Bucks County, for $650 million in cash.

Founded in 206, Eusa employs about 180 employees at its offices in Langhorne; Oxford, United Kingdom; and Lyon, France. Bryan Morton, who is founder, president and CEO of Eusa, will remain with the company, according to a statement issued by the companies.

Under the terms of the transaction, an additional $50 million cash payment would be made once Eusa's lead product, Erwinaze, attains an undisclosed U.S. net sales target in 2013. Approved by the Food and Drug Administration last November, Erwinaze is used to treat patients with acute lymphoblastic leukemia, a rare disease that strikes about 3,600 people under the age of 20 in the United States each year.

Eusa said its first-quarter net sales were about $46 million. Jazz said it expects the transaction will add revenue of $210 million to $230 million in 2013. In 2011, Jazz had total revenues of $272 million, led by $233 million in sales of Xyrem, a treatment for excessive daytime sleepiness.

A specialty biopharmaceutical company, Jazz was formed as the result of the combination of Palo Alto, Calif.-based Jazz Pharmaceuticals Inc. and Dublin-based Azur Pharma PLC as of Jan. 12.

Jazz had 431 employees as of Feb. 21 spread between its offices in Dublin, Palo Alto and Philadelphia, where its U.S. commercial operations lease about 10,000 square feet at 1818 Market St.

The acquisition, which is expected to closed in June, was announced after the trading had ended for the day on U.S. stock exchanges. Shares of the publicly traded Jazz closed at $45.20, down 18 cents.

Eusa is a privately held company whose venture capital investors included Essex Woodlands, 3i, Advent Venture Partners, SV Life Sciences, TVM Capital, NeoMed and NovaQuest.