Emdeon Inc shares started trading for $17.75 in their debut on Wednesday following their initial public offering, and rose to as much as $18.24.

In early trading, Emdeon shares were changing hands for $17.85, or 15.1 percent over the IPO price of $15.50 set Wednesday evening.

Emdeon, which provides payment and billing systems to U.S. health care companies, sold 23.7 million shares and raised about $367 million in an IPO led by Morgan Stanley, Goldman Sachs & Co, UBS Investment Bank and Barclays Capital.

Emdeon's IPO is the third largest of the year in the United States, excluding those by real estate investment trusts.

 (Reporting by Phil Wahba, editing by Gerald E. McCormick)