The shares of United Therapeutics Corporation (NASDAQ:UTHR - 46.24) are sitting out the broad-market rebound, with the stock last seen more than 13% lower. Against this backdrop, it looks like a handful of option bears -- a group that's expanded over the past couple of weeks -- are cashing in their chips.

In early trading, UTHR has already seen roughly 1,700 puts cross the tape -- about 10 times its average intraday put volume. Most popular is the now in-the-money November 50 put, which has seen close to 1,200 contracts exchanged. Ninety-four percent of the newly front-month puts traded at the bid price, and implied volatility has dropped more than 32 percentage points, underscoring our theory of sell-to-close activity.

As alluded to earlier, bearish bets were growing increasingly popular on UTHR. On the International Securities Exchange (ISE), Chicago Board Options Exchange (CBOE), and NASDAQ OMX PHLX (PHLX), the stock's 10-day put/call volume ratio of 0.74 ranks in the 72nd percentile of its annual range. In other words, option traders have bought to open UTHR puts over calls at a faster-than-usual clip during the past couple of weeks.

Elsewhere on Wall Street, there are likely more than a few short sellers applauding today's retreat. Despite depleting by 12.1% during the most recent reporting period, short interest still accounts for about 8.5% of UTHR's total available float. In fact, at the equity's average daily trading volume, it would take around a week to repurchase all of these pessimistic positions.

However, not everyone has capitulated to the bears' club. UTHR sports six "strong buy" endorsements from analysts, compared to six lukewarm "holds" and not a single "sell" or worse recommendation. That sentiment tide appears to be shifting, though; already today, BMO downgraded the stock to "market perform" from "outperform," while J.P. Morgan lowered its opinion to "underweight" from "neutral."

Fueling UTHR's plunge was a regulatory setback, with the FDA rejecting the company's oral drug to treat pulmonary arterial hypertension. Specifically, the FDA cited treprostinil diethanolamine's inability to show a statistically significant effect in patients taking the six-minute walk test, and questioned the drug's inability to keep the patients' condition from worsening.

At last check, UTHR has surrendered 13.2% to trade near $46.24. This bearish gap has negated the security's year-to-date surplus, and places the shares south of their 200-day moving average, which hasn't been breached since mid-June.