United upswing

Despite receiving two complete response letters from FDA for pulmonary arterial hypertension drug treprostinil in the past six months, United Therapeutics Inc.(NASDAQ:UTHR) shares continue to climb, due in part to the company's bulging coffers and history of share buybacks.

The company declined to disclose details of last week's second complete response letter for the oral compound, but did say FDA did not raise any issues beyond those in the first letter last October. United shares dropped $8.99 (17%) to $44.29 on Oct. 24, 2012, after the company disclosed it had received that letter, but the stock has been gaining ever since, hitting a 52-week high of $63.11 on March 20...