Loss from continuing operations before provision for income tax for the Company’s domestic and international operations was as follows (in thousands):

At December 31, 2019, the Company has concluded that it is more likely than not that the Company may not realize the benefit of its deferred tax assets due to its history of losses. There was no provision for income tax recorded for the year ended December 31, 2019 as a result of the current year losses. The provision for income taxes for the year ended December 31, 2018 was $0.2 million. The provision for income taxes relates only to withholding taxes for the year ended December 31, 2018 because the Company has incurred operating losses since inception. Accordingly, the net deferred tax assets have been fully reserved. The provision for income taxes consists of the following (in thousands):

	Year Ended December 31,
	2019			2018
Current
U.S. federal	$	—		$	—
U.S. state		—			—
Non-U.S.		—			240
Total current		—			240
Deferred
U.S. federal		(8,551	)		(9,164	)
U.S. state		3,299			(1,903	)
Non-U.S.		—			—
Total deferred		(5,252	)		(11,067	)
Valuation allowance		5,252			11,067
Total	$	—		$	240

Deferred income taxes reflect the tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting and income tax purposes. A valuation allowance is established when uncertainty exists as to whether all or a portion of the net deferred tax assets will be realized. Components of the net deferred tax assets as of December 31, 2019 and 2018, are as follows (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	531,970		$	524,377
Research and development credits		80,488			81,583
Capitalized research		44			557
Milestone Rights		1,528			3,521
Accrued expenses		1,951			1,156
Loss on purchase commitment		22,167			23,194
Non-qualified stock option expense		3,128			2,551
Capitalized patent costs		4,964			5,090
Other		147			669
Lease liability		827			—
Interest expense limitation		1,167			—
Depreciation		21,132			22,560
Deferred Product Revenue & Costs		2,062			107
Total net deferred tax assets		671,575			665,365
Valuation allowance		(670,617	)		(665,365	)
Net deferred tax assets	$	958		$	—

Deferred tax liabilities:
Right of use asset	$	(751	)	$	—
Other prepaids		(207	)		—
Total deferred tax liabilities		(958	)		—
Net deferred tax assets	$	—		$	—

The Company’s effective income tax rate differs from the statutory federal income tax rate as follows for the years ended December 31, 2019 and 2018:

	Year Ended December 31,
	2019			2018
Federal tax benefit rate		21.0	%		21.0	%
Permanent items		(3.3	)		1.0
Tax law changes		(2.7	)		(0.7	)
Stock based compensation		(0.9	)		(6.5	)
Tax attribute expirations		(4.0	)		(1.6	)
Foreign withholding tax		—			(0.3	)
Valuation allowance		(10.1	)		(13.2	)
Effective income tax rate		0.0	%		-0.3	%

As of December 31, 2019 and 2018, management assessed the realizability of deferred tax assets. Management evaluated the need for an amount of any valuation allowance for deferred tax assets on a jurisdictional basis. This evaluation utilizes the framework contained in ASC 740, Income Taxes, wherein management analyzes all positive and negative evidence available at the balance sheet date to determine whether all or some portion of the Company’s deferred tax assets will not be realized. Under this guidance, a valuation allowance must be established for deferred tax assets when it is more likely than not (a probability level of more than 50%) that the Company may not realize the benefit of its deferred tax assets. In assessing the realization of the Company’s deferred tax assets, the Company considers all available evidence, both positive and negative.

In concluding on the evaluation, management placed significant emphasis on guidance in ASC 740, which states that “a cumulative loss in recent years is a significant piece of negative evidence that is difficult to overcome.” Based upon available evidence, it was concluded on a more-likely-than-not basis that all deferred tax assets were not realizable as of December 31, 2019. Accordingly, a valuation allowance of $670.6 million has been recorded to offset this deferred tax asset. During the years ended December 31, 2019 and 2018, the change in the valuation allowance was $5.3 million and $11.1 million, respectively.

At December 31, 2019, the Company had federal and state net operating loss carryforwards of approximately $2.1 billion and $1.3 billion available, respectively, to reduce future taxable income. $117.8 million of the federal losses do not expire and the remaining federal and state losses have started expiring, beginning in the current year through various future dates.

Pursuant to Internal Revenue Code (“IRC”) Sections 382 and 383, annual use of the Company’s federal and state net operating loss and research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. As a result of the Company's initial public offering, an ownership change within the meaning of Internal Revenue Code Section 382 occurred in August 2004. As a result, federal net operating loss and credit carryforwards of approximately $216.0 million are subject to an annual use limitation of approximately $13.0 million. The annual limitation is cumulative and therefore, if not fully utilized in a year can be utilized in future years in addition to the Section 382 limitation for those years. We have completed a Section 382 analysis beginning from the date of our initial public offering through to the end of the previous tax year regarding whether additional limitations may be placed on the net operating loss carryforwards and other tax attributes, and no additional changes in ownership that met Section 382 study ownership change threshold has been identified through December 31, 2019. There is a risk that changes in ownership may occur in tax years after December 31, 2019. If a change in ownership were to occur, our net operating loss carryforwards and other tax attributes could be further limited or restricted. If limited, the related asset would be removed from the deferred tax asset schedule with a corresponding reduction in the valuation allowance. Due to the existence of the valuation allowance, limitations created by future ownership changes, if any, related to the Company’s operations in the U.S. will not impact the Company’s effective tax rate.

At December 31, 2019, the Company had $54.2 million of U.S. federal research and development credits which expire beginning in 2024, and $26.3 million of state research and development credits. The California credits do not expire and the New Jersey credits will begin to expire in 2020. The Company also had two types of credits in Connecticut of which $15.7 million do not expire and $0.9 million will begin to expire in 2020. Due to the existence of the valuation allowance, the expiration of the research and development credits will not impact the Company’s consolidated statements of operations.

The Company files U.S. federal and state income tax returns in jurisdictions with varying statutes of limitations. In the normal course of business the Company is subject to examination by taxing authorities throughout the country. These audits could include examining the timing and amount of deductions, the allocation of income among various tax jurisdictions and compliance with federal, state and local laws. The Company’s tax years since 2015 remain subject to examination by federal, state and foreign tax authorities.

The Company considers its undistributed earnings of foreign subsidiaries to be permanently reinvested in foreign operations and has not provided for U.S. income taxes on such earnings. As of December 31, 2019 the Company had no undistributed earnings from its foreign subsidiaries.

The Company adopted Accounting Standards Codification (“ASC”) Topic 842 – Leases, on January 1, 2019. Under Topic 842, the Company is required to recognize the assets and liabilities that arise from most operating leases on the balance sheet. Upon adoption, no change in retained earnings was recorded related to income taxes as the Company maintains a full valuation allowance. As of the implementation date, an adjustment of $0.7 million was recorded as a deferred tax liability and an adjustment of $0.7 million was recorded as a deferred tax asset. See above for more information about the non-income tax impact of the adoption of the new leasing standard.

Legislation enacted in 2017, informally titled the Tax Cuts and Jobs Act of 2017, subjects a U.S. shareholder to tax on global intangible low-taxed income (“GILTI”) earned by certain foreign subsidiaries. The FASB Staff Q&A, Topic 740, No. 5, Accounting for Global Intangible Low-Taxed Income, states that an entity can make an accounting policy election to either recognize deferred taxes for temporary basis differences expected to reverse as GILTI in future years or to provide for the tax expense related to GILTI in the year the tax is incurred as a period expense only. The Company has elected to account for GILTI in the year the tax is incurred.