adverse effect on the prospects of our business. Further, our assumptions relating to our cash requirements may differ materially from our actual requirements because of a number of factors, including significant unforeseen delays in the regulatory approval process, changes in the timing, scope, focus and direction of clinical trials and costs related to commercializing the product.
We have funded our operations through a combination of private placements and public offerings of its securities in each of 2000, 2003, 2009, 2010, 2011, 2012, 2013, 2015, 2016, 2018 and 2019, including registered direct offerings in 2007, 2009 and 2013, “at the market” equity offering programs in 2012 and 2013, and by the private placement of convertible notes in 2016 and 2018, and, most recently, in July and August 2019, we raised $29.5 million in the closing of two private placements of convertible preferred stock and warrants to purchase common stock. For a detailed discussion of our various sales of debt and equity securities see Notes 8, 9, and 14 to our condensed consolidated financial statements as well as Notes 10 and 11 to our audited consolidated financial statements.
In October 2018, we filed a registration statement on FormS-3 with the SEC, which was declared effective on December 21, 2018 and allowed us to offer and sell, from time to time in one or more offerings, up to $100.0 million of common stock, preferred stock, warrants, debt securities and stock purchase contracts as it deems prudent or necessary to raise capital at a later date. We lost our FormS-3 eligibility due to the late filing of our Annual Report for the year ended December 31, 2018.
Results of Operations for the Year Ended December 31, 2018; Comparisons of Results of the Years Ended December 31, 2018 and 2017
Revenue
We recorded approximately $3.4 million in product revenue during the year ended December 31, 2018. During the same period in 2017, We recorded $2.7 million in total revenue related to product sales. The year over year increase is a result of greater product sales in 2018 as we continued to see increased market acceptance of its product in the EU, particularly in Germany where the establishment of the ZE code has contributed to increased treatments.
Additionally, we recorded approximately $29,000 in other revenue which is related to the amortization of certain payments pursuant to the medac License.
The adoption of ASC 606 on January 1, 2018 had no impact on the amount and timing of revenue recognition related to product sales.
Cost of Goods Sold
During the year ended December 31, 2018, we recognized cost of goods sold of approximately $1.0 million related to product revenue of $3.4 million as compared to cost of goods sold of approximately $0.7 million related to product revenue of $2.7 million in the comparable prior period.
The increase in cost of goods sold is commensurate with the increase in revenue.
Selling, General and Administrative Expenses
For the year ended December 31, 2018, selling, general and administrative expenses increased to $9.8 million from $9.7 million for the year ended December 31, 2017. The slight increase reflects our efforts to focus its resources on its clinical development program.
Research and Development Expenses
For the year ended December 31, 2018, research and development expenses increased to $19.7 million from $10.5 million for the year ended December 31, 2017. The increase of $9.2 million is primarily due to the ongoing efforts of the FOCUS Trial.
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