salary, benefits and commission costs as a result of an expansion of our commercialization activities, including an increase in headcount which was offset by lower travel and consulting expenses resulting from the COVID-19 pandemic.
General and Administrative
General and administrative expenses increased by $3.5 million, or 95%, to $7.3 million for the nine months ended September 30, 2020 from $3.7 million for the nine months ended September 30, 2019. The increase was primarily due to an increase in insurance costs of $1.5 million, higher professional, legal and consulting fees of $0.6 million, higher non-cash stock-based compensation expense of $0.6 million, higher salary and benefits of $0.3 million, increased board fees of $0.2 million and additional bad debt expense of $0.2 million which were partially offset by the cost containment actions taken in response to the COVID-19 pandemic.
Research and Development
Research and development expenses decreased by $0.1 million, or 4%, to $3.1 million for the nine months ended September 30, 2020 from $3.2 million for the nine months ended September 30, 2019 primarily due to a decrease in licensing payments of $0.5 million and reduced outside development expenses partially offset by higher salaries and benefits.
Interest Expense
Interest expense was $2.7 million for both the nine months ended September 30, 2020 and 2019. The slight decrease of $64,000, or 2%, for the nine months ended September 30, 2020 was primarily due a lower interest rate during the nine months ended September 30, 2020 compared to the prior period.
Change in Fair Value of Preferred Stock Warrant Liability
For the nine months ended September 30, 2019, we recognized a loss of $4,000 due to the change in the fair value of the preferred stock warrant liability.
Other Income
Other income was $0.2 million for both the nine months ended September 30, 2020 and 2019.
Liquidity and Capital Resources
Overview
As of September 30, 2020, we had cash and cash equivalents of $81.5 million, working capital of $83.7 million and an accumulated deficit of $188.9 million. As of December 31, 2019, we had cash, cash equivalents and short-term investments of $54.6 million, working capital of $57.6 million and an accumulated deficit of $167.9 million.
On November 13, 2019, we closed our IPO in which we issued and sold 4,398,700 shares of our common stock at a public offering price of $13.00 per share, which included 398,700 shares of our common stock sold pursuant to the underwriters’ option to purchase additional shares. We received net proceeds of $50.6 million after deducting underwriting discounts and commissions and other expenses.
On June 30, 2020, we closed an underwritten public offering in which we issued and sold 3,000,000 shares of our common stock at a public offering price of $16.00 per share. We received net proceeds of $44.7 million after deducting underwriting discounts, commissions and other offering expenses.
We have incurred operating losses since our inception, and we anticipate that our operating losses will continue in the near term as we seek to invest in our sales and marketing initiatives to support our growth in existing and new markets and in additional research and development activities. We will also continue to incur additional costs operating as a