4. Notes Payable

The Company has outstanding amounts due under a loan and security agreement with Oxford Finance LLC and Midcap Financial (the “Credit Facility”) entered into in March 2014. All promissory notes issued under the Credit Facility are collateralized by substantially all of the Company’s personal property, other than intellectual property. There are no financial covenants associated with the debt facility; however, there are negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering or granting a security interest in the Company’s intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and certain other business transactions. As of June 30, 2015 and December 31, 2014, notes payable consist of the following:


	June 30, 2015			December 31, 2014
Notes payable	$	7,500		$	7,500
Less: current portion		(2,820	)		(1,381	)

Notes payable, net of current portion		4,680			6,119
Debt discount, net of accretion		(56	)		(79	)
Accretion related to final payment		227			137

Notes payable, net of discount, long term	$	4,851		$	6,177

As of June 30, 2015, estimated future principal payments due are as follows:


Years Ending December 31,
2015	$	1,381
2016		2,936
2017		3,183

	$	7,500

During the three months ended June 30, 2015 and 2014, the Company recognized $213 and $443, respectively, of interest expense related to the Credit Facility. During the six months ended June 30, 2015 and 2014, the Company recognized $426 and $445, respectively, of interest expense related to the Credit Facility. The effective annual interest rate of the outstanding debt under the Credit Facility is approximately 14%.