INCOME TAXES

The following table summarizes our effective tax rate and income tax benefit from continuing operations for the three months ended March 31, 2019 and 2018 (in thousands except for percentages):



	Three Months Ended March 31,
	2019			2018
Effective tax rate	—		%	12		%
Income tax benefit	$	(137	)	$	(8,000	)

For the three months ended March 31, 2019, we recognized an income tax benefit of $0.1 million, representing an effective tax rate of 0%. The income tax benefit for the three months ended March 31, 2019 primarily related to state taxes and the offset of the recognition of the income tax expense recorded in other comprehensive loss associated with the increase in the value of available-for-sale securities that we carried at fair market value during the period. The difference between the statutory federal tax rate of 21% and the effective tax rate for the three months ended March 31, 2019, was primarily attributable to the valuation allowance established against our current period losses generated and the non-deductible IPR&D expense related to the Perosphere acquisition. We have established a valuation allowance on our deferred tax assets other than refundable alternative minimum tax (“AMT”) credits to the extent that our existing taxable temporary differences would not be available as a source of income to realize the benefits of those deferred tax assets.

For the three months ended March 31, 2018, we recognized an income tax benefit of $8.0 million, representing an effective tax rate of 12%. The difference between the statutory federal tax rate of 21% and the effective tax rate for the three months ended March 31, 2018 was primarily attributable to the impact of the establishment of a valuation allowance related to certain deferred tax assets, the impact of non-deductible stock compensation, and other non-deductible expenses, partially offset by state income taxes and orphan drug tax credits.

The primary driver of the decrease in tax benefit for the three months ended March 31, 2019 as compared to the three months ended March 31, 2018 is the increase in valuation allowance on our current period losses generated.