WATERTOWN, Mass. - Athenahealth, the web-based medical billing services provider, announced today an agreement to acquire Epocrates Inc., maker of mobile physicians' applications, for $11.75 per share, or roughly $293 million.

The closing is expected to happen in the second quarter of 2013. The sale price is 22 percent above Epocrates' Jan. 4 closing rate on the NASDAQ stock exchange, according to a statement from athenahealth.

Epocrates makes mobile applications used by doctors in the office to look up drug interactions, diagnosis codes for billing and get medical news. The service, typically accessed by a handheld device like a smartphone, is used by 330,000 physicians. 

According to Forbes magazine, the acquisition would be the largest ever for athenahealth. Last month the company announced plans to buy the 29-acre Arsenal on the Charles office park from Harvard University for $168.5 million. Athenahealth's home offices have been located in a portion of the Arsenal complex since 2005.

Athenahealth opened offices in Belfast in 2008 and currently has over 500 employees there. In 2011 the company bought the 400-acre Point Lookout Resort in Northport for $7.7 million.

Contact Ethan Andrews by e-mail at news@penbaypilot.com