Shares of Dexcom (DXCM) tumbled over 40% in extended trading Thursday after the company reported second-quar🌼ter earnings that missed estimates and slashed its full-year revenue 🀅guidance.

The maker of glucose monitors said it now expects full-year organic revenue growth of 11% to 13%, down from its projection in April of 17% to 21%.

Dexcom's revenue in the second quarter grew 15% year-over-year to $1 billion, roughly in line with analysts' estimates compiled by Visible Alpha. However, net income of $143.5 million or 35 cents per share missed expectations.

“While Dexcom advanced several key strategic initiatives 𒐪in the second quarter, our execution did not meet our high standards,” CEO Kevin Sayer said in a release, adding “we are taking action to improve our execution and best position ourselves for continued long-term growth.”

Dexcom also announced a $750 million stock buyback program.

Shares of Dexcom were down 40.1% at $64.50 in extended trading as of 5:40 p.m. ET Thursday following the release.