5. PATENT COSTS

We amortize intangible assets with definite lives on a straight-line basis over their remaining estimated useful lives, ranging from one to twelve years, and review for impairment on a quarterly basis and when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. As of June 30, 2016, there was no indicator that an impairment existed.

We capitalized legal patent costs related to patent prosecution and maintenance. For the six months ended June 30, 2016, we increased our capitalized patent costs by approximately $11,200, based on reports provided to us by Endo. These patent costs are creditable against future royalty revenues. For each period presented below, net patent costs consisted of:

	June 30, 2016			December 31, 2015
Patents	$	708,474		$	697,260
Accumulated amortization		(441,374	)		(422,054	)
	$	267,100		$	275,206

The amortization expense for patents for the three and six months ended June 30, 2016 was approximately $9,700 and $19,300, respectively, and the amortization expense for patents for the three and six months ended June 30, 2015 was approximately $12,000 and $23,000, respectively. The estimated aggregate amortization expense for the remaining six months of 2016 and each of the years below is approximately as follows:

July 1, 2016 to December 31, 2016	$	19,500
2017		38,700
2018		38,700
2019		38,700
2020		27,400
Thereafter	$	104,100