Shares of MannKind Corp. plummeted more than 20 percent Friday, a day after the company released second-quarter financial results that missed Wall Street estimates for revenue.

The Westlake Village pharmaceutical firm reported a net loss of about $22.7 million. Earnings were -16 cents a share, compared to -35 cents a share a year ago.

Earnings for the quarter beat by about 4 cents estimates from MannKind’s sole Wall Street analyst, who had expected earnings of -20 cents a share, according to Thomson Financial.

MannKind’s ’s primary product is an inhalable insulin called Afrezza. Revenue for the quarter was about $3.9 million, compared to $2.16 million in the year prior. The Mannkind analyst had expected revenue of $4.8 million.

MannKind stock has lost more than half of its value since the start of the year. In a monthly conference call with investors, Chief Executive Michael Castagna suggested that the firm’s stock price was not a reflection of the company’s value. The firm – which holds more than 800 patents – recently expanded its pipeline with the addition of a pulmonary arterial hypertension drug that it has dubbed Treprostinil Technosphere. It also announced July 27 that it has entered into an agreement with Tanner Pharma Group for international distribution of Afrezza.

“Unfortunately, the barometer that I measure shows we have failed to see any major appreciation in our stock price,” Castagna said. “I believe we are undervalued when I look at the sum of the parts.”

Shares of MannKind fell 35 cents, or 23.3 percent, on Friday to close at $1.15 on the Nasdaq.