Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What's happening: Shares in Pernix Therapeutics Holdings (NASDAQ: PTX) dropped by 15% today as investors digest the news that the drugmaker has acquired Zogenix's (ZGNX) Zohydro ER pain-killer business.

Why it's happening: Pernix agreed to hand over up to $383.5 million to Zogenix to get its hands on three Zohydro extended release hydrocodone products, including an abuse deterrent version that was developed to ease worries over potential misuse of the painkiller.

As part of the deal, Pernix is paying Zogenix $100 million up front, comprising of $30 million in cash, $20 million in Pernix common stock, and a $50 million short term promissory note. Pernix also agreed to potentially pay Zogenix regulatory and commercial sales milestone payments that could total as much as $283.5 million.

In addition to the Zohydro drug line-up, Pernix is also being transferred patents, the Zohydro sales team, and other Zogenix personnel.

Now what: Investors have cheered on Pernix this past year, sending shares up by more than 200% on enthusiasm for its drugs Treximet, for the treatment of migraine, and Silenor, for the treatment of insomnia.

Thanks to those drugs, Pernix sales jumped 125% year-over-year to $53.8 million last quarter. Importantly, sales growth led to the company reporting non-GAAP EPS of $0.18 last year, up significantly from a loss of -$0.06 in 2013.

Although Pernix's acquisition of Zohydro could yield intriguing cross-selling benefits given that chronic pain sufferers also have trouble sleeping, investors seem to be worrying that the price and personnel costs of this deal could weigh down profit this year.

Investors are right to be cautious. Zohydro's launch was hindered by a barrage of pushback over concerns surrounding hydrocodone and its addictiveness. As a result, despite launching a year ago, Zohydro's annualized sales are tracking at just $23 million.

Although I'm not convinced that Zohydro can be a top seller, Pernix is admittedly an intriguing company. It's cobbled together an intriguing product lineup, and if it can deliver on the cross-selling synergies it thinks it can, this could be a lucrative deal. As a result, this is a stock I'm going to keep my eyes on.