Intangible assets at December 31, 2019 and 2018 consist of the following:

Under the previous contract manufacturing agreement between ADMA and BPC, intermediate by-products derived from the manufacture of ASCENIV were property of Biotest. As a result of the Biotest Transaction, ADMA obtained the right to these intermediate products, which are being amortized over a period of seven years. The intangible rights to Nabi-HB is also being amortized over a period of seven years.

The customer contract pertains to a contract manufacturing agreement with a third-party customer that the Company assumed upon the consummation of the Biotest Transaction. On December 22, 2017, Company and the customer entered into an amendment to this contract which reduced the number of batches the Company was committed to supply to the customer. The remaining required production volume was 13 batches over 2018 and 2019. The Company has fulfilled this obligation to the customer in its entirety as of December 31, 2019, the date of expiration of the contract, as amended.

Amortization expense related to the Company’s intangible assets for the years ended December 31, 2019 and 2018 was $0.8 million. Estimated aggregate future aggregate amortization expense for the next five years is expected to be as follows: