6. Intangible Assets

Intangible assets consist of patent defense costs, which are legal fees incurred in conjunction with defending patents for Oxtellar XR and Trokendi XR. We amortize those costs over the useful life of the respective patents.

The following sets forth the gross carrying amount and related accumulated amortization of the intangible assets, in thousands of dollars:


	Weighted-	December 31,		December 31,
	Average Life	2018		2017
Capitalized patent defense costs	4.00 - 8.25 years	$	44,724	$	44,185
Less accumulated amortization			(13,356)		(8,166)
		$	31,368	$	36,019

In March 2017, the Company entered into two settlements with several companies related to Trokendi XR patent litigation, which effectively reduced the remaining life of the Trokendi XR patents. The remaining unamortized aggregate capitalized patent defense costs for Trokendi XR have subsequently been amortized over the reduced remaining useful life of the patents at issue, or January 1, 2023. This is the date the Company is obligated under the settlements to grant a non-exclusive license to the patents at issue.

Amortization expense on intangible assets was approximately $5.2 million, $6.9 million and $1.3 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Anticipated annual amortization expense on intangible assets for each of the next four years from, 2019 to 2022, is approximately $5.2 million per year. Anticipated annual amortization expense on intangible assets for the fifth year, 2023, is approximately $2.5 million.

No indicators of impairment were identified.