million of a variety of securities including common stock, preferred stock, warrants, depositary shares, debt securities, purchase contracts, purchase units or any combination of such securities during the three-year period that commenced upon the 2018 Shelf Registration becoming effective. The 2018 Shelf Registration is now expired.
On October 1, 2018, we entered into the Athyrium Credit Facility with Athyrium for up to $110.0 million. The Athyrium Credit Facility provided for a Term Loan A in the aggregate principal amount of $75.0 million, and a Term Loan B in the aggregate principal amount of $35.0 million which we did not draw down. On May 4, 2021, concurrently with the closing of the Loan Agreement with Oxford Finance and the borrowing of the tranche A loan, we utilized substantially all of the proceeds from the tranche A term loan to repay in full all outstanding amounts owed under the Athyrium Credit Facility, under which we had an aggregate principal amount of $75.0 million of indebtedness outstanding. We terminated all commitments by Athyrium to extend further credit under the Athyrium Credit Facility and all guarantees and security interests granted by us thereunder. In connection with the termination of the Athyrium Credit Facility, we paid to the lenders a prepayment premium of $2.25 million and an exit fee of $0.8 million. The transaction resulted in a loss on extinguishment of debt of $5.4 million, consisting of the prepayment premium, the unamortized debt discount and the unaccreted exit fee.
On October 5, 2018, we sold 7,500,000 shares of common stock in an underwritten offering pursuant to the 2018 Shelf Registration at a public offering price of $8.25 per share, before underwriting discounts and commissions. In addition, the underwriters were granted an overallotment option to purchase an additional 1,125,000 shares of the common stock at the same public offering price, less underwriting discounts and commissions. On October 11, 2018, the underwriters exercised in full their option to purchase the overallotment shares. The total number of shares sold by us in the offering was 8,625,000 shares, resulting in net proceeds to us, after underwriting discounts and offering expenses, of $66.1 million. In connection with the filing of the 2018 Shelf Registration, we entered into a sales agreement with Jefferies, pursuant to which we could issue and sell, from time to time, up to an aggregate of $50.0 million of our common stock in an ATM Offering, through Jefferies, as sales agent. Through the first quarter of 2020, we issued an aggregate of 4,945,605 shares of our common stock under the ATM Offering, resulting in net proceeds to us of $25.6 million. On March 10, 2020, we suspended and terminated the prospectus related to the ATM Offering.
On March 11, 2020, we sold 16,000,000 shares of our common stock in an underwritten offering pursuant to the 2018 Shelf Registration at a public offering price of $7.89 per share, resulting in net proceeds of $118.2 million, after underwriting discounts, commissions, and offering expenses. In addition, the underwriters of the offering were granted the option for a period of 30 days to purchase up to an additional 2,400,000 shares of common stock offered in the public offering at the public offering price, less underwriting discounts, commissions and offering expenses. On April 3, 2020, the underwriters exercised their option and purchased an additional 979,371 shares of common stock at $7.89 per share, resulting in net proceeds to us of $7.2 million, after underwriting discounts, commissions, and offering expenses. The total number of shares sold by us in the offering was 16,979,371, resulting in total net proceeds to us, after underwriting discounts, commissions and offering expenses, of $125.4 million.
Under the 2018 Shelf Registration, which has now expired, we issued an aggregate of 30,549,976 shares of common stock, including under the ATM Offering, resulting in aggregate gross proceeds to us of $231.7 million.
On May 7, 2020, we filed our shelf registration statement on Form S-3 that was declared effective by the SEC on May 7, 2020, or the 2020 Shelf Registration, under which we may offer and sell up to $350.0 million of a variety of securities including common stock, preferred stock, warrants, depositary shares, debt securities or units during the three-year period that commenced upon the 2020 Shelf Registration becoming effective. In connection with the filing of the 2020 Shelf Registration, we entered into an amended and restated sales agreement with Jefferies, pursuant to which we may issue and sell, from time to time, up to an aggregate of $75.0 million of our common stock under our ATM Offering. Through December 31, 2021, we issued and sold an aggregate of 8,581,257 shares of our common stock under the ATM Offering, resulting in net proceeds of $61.8 million, which included 837,257 and 5,583,329 shares of common stock issued and sold during the three and six months ended June 30, 2021, respectively, resulting in net proceeds of $6.0 milllion and $40.7 million, respectively. As of June 30, 2022, there was $11.3 million of shares of common stock remaining under the ATM Offering that we may issue and sell in the future and, excluding the shares of common stock that may be offered under our ATM Offering, there was $275.0 million of securities available to be issued under the 2020 Shelf Registration.