The following table presents the composition of debt as of March 31, 2019 and December 31, 2018 (in thousands):

	March 31, 2019			December 31, 2018
Outstanding principal	$	30,000		$	30,000
Accrued final payment fees		1,555			1,468
Less debt discounts		(983	)		(1,073	)
Long-term debt, net	$	30,572		$	30,395

For the three months ended March 31, 2019, the Company recognized interest expense of $0.9 million, of which $0.7 million was cash and $0.2 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees. For the three months ended March 31, 2018, the Company recognized interest expense of $0.9 million, of which $0.7 million was cash and $0.2 million was non-cash interest expense related to the amortization of deferred debt issuance costs and accrual of final payment fees.

In March 2017, the Company entered into a loan and security agreement with Oxford Finance LLC, or Oxford, for a credit facility that replaced its previous $25.0 million credit facility with Oxford and which allowed it to borrow up to $35.0 million in three tranches of term loans: a Term A Loan in the amount of $25.0 million, which was drawn down immediately upon closing in March 2017, a Term B Loan in the amount of $5.0 million, which was drawn down in December 2017, and a Term C Loan in the amount of $5.0 million, which became available to the Company upon the achievement of $45.0 million of trailing twelve month revenues during the second quarter of 2018. Upon achieving the required revenue milestone, the Company had 60 days to notify Oxford if it elected to borrow the Term C Loan. As a result of completing its IPO on July 2, 2018 and receiving the net proceeds therefrom, the Company elected not to borrow the additional $5.0 million, and it is no longer available to the Company. Each term loan accrues interest from the date of borrowing through the date of repayment at a floating per annum rate of interest, which resets monthly and is equal to the greater of (a) 8.15% or (b) the 30-day U.S. LIBOR on the last business day of the month plus 7.38%. The Company was also required to issue to Oxford at the date of each borrowing warrants to purchase its Series F or later series of convertible preferred stock with a seven-year term and in an amount equal to 3.95% of the first $5.0 million of each tranche borrowed. The credit facility matures and all amounts borrowed thereunder are due on March 1, 2022. As of March 31, 2019, the Company had borrowed and had outstanding an aggregate of $30.0 million of principal under the credit facility.

The Term A Loan featured an interest-only period through March 2019, during which time the Company was required to make monthly interest payments, after which time the Company was required to make monthly payments of principal and interest based on a 36-month amortization schedule. However, due to the achievement of $45.0 million of revenues during fiscal year 2018, the interest-only period was extended for an additional 12 months through March 2020, after which time the Company will be required to make monthly payments of principal and interest based on a 24-month amortization schedule. In connection with the drawdown of the Term A Loan, the Company issued to Oxford a warrant to purchase shares of its Series F convertible preferred stock. On July 2, 2018, this convertible preferred stock warrant converted into a warrant to purchase 20,303 shares of the Company’s common stock at an exercise price of $9.73 per share. The warrant will expire in March 2024.

The Term B Loan featured an interest-only period through March 2019, during which time the Company was required to make monthly interest payments, after which time the Company was required to make monthly payments of principal and interest based on a 36-month amortization schedule. However, due to the achievement of $45.0 million of revenues during the fiscal year 2018, the interest-only period was extended for an additional 12 months through March 2020, after which time the Company will be required to make monthly payments of principal and interest based on a 24-month amortization schedule. In connection with the drawdown of the Term B Loan, the Company issued to Oxford a warrant to purchase shares of its Series F convertible preferred stock. On July 2, 2018, this convertible preferred stock warrant converted into a warrant to purchase 20,303 shares of the Company’s common stock at an exercise price of $9.73 per share. The warrant will expire in December 2024.

In addition to principal and interest payments due under the credit facility, the Company is required to make final payment fees to Oxford due upon the earlier of prepayment or maturity of each tranche, which increased as a result the extension of the interest-only period and are now equal to 8.5% and 7.5% of the principal amounts of the Term A and Term B Loans, respectively. The Company accrues the estimated final payment fees using the effective interest rate, with a charge to non-cash interest expense, over the term of borrowing for each tranche. As of December 31, 2018, the effective interest rates for the Term A and Term B Loans were 11.87% and 12.14%, respectively. As of December 31, 2017, the effective interest rates for the Term A and Term B Loans were 10.7% and 11.6%, respectively. If the Company prepays its term loans prior to their respective scheduled maturities, it will also be required to make prepayment fees to Oxford equal to 3% if prepaid on or before the first anniversary of funding, 2% if prepaid after the first and on or before the second anniversary of funding, or 1% if prepaid after the second anniversary of funding of the principal amounts borrowed.

The Company’s obligations under the credit facility are secured by a first priority security interest in substantially all of its assets, other than its intellectual property. The Company has agreed not to pledge or otherwise encumber any of its intellectual property. The loan and security agreement related to the credit facility includes a financial maintenance covenant that requires the Company to achieve at least 75% of its trailing 12-month forecasted revenues, as measured each month in accordance with a forecast that the Company provided to Oxford upon signing the agreement and future forecasts that the Company is required to deliver to Oxford each year for the life of the credit facility, as well as customary affirmative and negative covenants. The Company was in compliance with all of the covenants under its credit facility as of March 31, 2019.

The loan and security agreement related to the credit facility contains events of default, including, without limitation, events of default upon: (i) failure to make payment pursuant to the terms of the agreement; (ii) violation of covenants; (iii) material adverse changes to the Company’s business; (iv) attachment or levy on the Company’s assets or judicial restraint on its business; (v) insolvency; (vi) significant judgments, orders or decrees for payments by the Company not covered by insurance; (vii) incorrectness of representations and warranties; (viii) incurrence of subordinated debt; (ix) revocation of governmental approvals necessary for the Company to conduct its business; and (x) failure by the Company to maintain a valid and perfected lien on the collateral securing the borrowing.

Based on a 24-month amortization of the outstanding principal amounts of the Term A and Term B Loans beginning on April 1, 2020 as discussed above, the following table sets forth by year the Company’s required future principal payments (in thousands):

Year:	Principal Payments
2019	$	-
2020		11,250
2021		15,000
2022		3,750
Total principal payments	$	30,000