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What: Shares of MannKind (NASDAQ:56400P706), a biopharmaceutical company focused on the development of inhaled diabetes therapies, tanked 15% in December, according to data from S&P Capital IQ, after two of its executives sold a portion of their stock holdings.

So what: Usually MannKind is a data-driven stock; however, the bulk of its weakness in December came within the first couple of days after Chief Operating Officer Hakan Edstrom and Corporate VP of Human Resources Diane Palumbo sold more than 258,000 shares of MannKind stock, combined. This followed the sale of 258,000 shares last month by two other MannKind insiders, although to be fair, 140,000 of the shares were based on an options exercise.

Also working against MannKind is a lack of an update on the upcoming launch of Afrezza, its recently approved inhaled diabetes drug. Though MannKind has been forthcoming with a rough launch range of the first-quarter of 2015, we still haven't heard anything on pricing -- and pricing will more than likely be the key to Afrezza's success since it'll probably cost more than a traditional injection.

Source: MannKind.

Now what: The good news for MannKind shareholders is December's 15% drop looks to be driven more on emotions than solid logic. Sure, we did see executives selling a portion of their holdings for a second straight month. However, the need to execute options before they expire, or an automatic sale toward the end of the year perhaps to cover an executives' tax liability to the IRS, is probably not a reason to be worried. Not all insider selling is inherently bad, and I wouldn't be too concerned with the recent pattern of selling in MannKind.

The real concern here is the lack of information leading up to the launch of Afrezza with licensing partner Sanofi. I fully expect to hear something regarding the launch this month, perhaps at the JPMorgan Healthcare Conference. However, until we have a launch date narrowed and pricing in place, I don't believe there are any major catalysts likely to send MannKind higher.