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 March 31, 2016, there was no indicator that an impairment existed.

We capitalized legal patent costs related to patent prosecution and maintenance. For the three months ended March 31, 2016, we increased our capitalized patent costs by approximately $5,400, 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:

	March 31, 2016			December 31, 2015
Patents	$	702,674		$	697,260
Accumulated Amortization		(431,698	)		(422,054	)
	$	270,976		$	275,206

The amortization expense for patents for the three months ended March 31, 2016 and 2015 was approximately $9,600 and $11,000, respectively. The estimated aggregate amortization expense for the remaining nine months of 2016 and each of the years below is approximately as follows:

April 1, 2016 to December 31, 2016	$	28,600
2017		38,100
2018		38,100
2019		38,100
2020		26,800
Thereafter	$	101,100