NEW YORK ( TheStreet) -- Shares of MannKind Corporation (Nasdaq: MNKD) were gapping down Friday morning with an open price 11.1% lower than Thursday's closing price. The stock closed at $5.06 Thursday and opened today's trading at $4.50. The average volume for MannKind has been 4.1 million shares per day over the past 30 days. MannKind has a market cap of $641.3 million and is part of the health care sector and drugs industry. MannKind Corporation, a biopharmaceutical company, focuses on the discovery, development, and commercialization of therapeutic products for diabetes and cancer. TheStreet Ratings rates MannKind as sell. The company's weaknesses can be seen in multiple areas, such as its generally disappointing historical performance in the stock itself and poor profit margins. You can view the full MannKind Ratings Report.