Nature of the Business and Basis of Presentation	12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation The Company is a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases caused by multi-drug resistant (“MDR”) bacterial infections with high unmet need. Since the Company’s inception in 2013, it has focused its efforts and financial resources on acquiring and developing product and technology rights, building our intellectual property portfolio and conducting research and development activities for its product candidates. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company believes that its novel product candidates, if successfully developed and approved, could provide meaningful benefits to patients suffering from serious rare diseases and life-threatening bacterial infections, in both the community and hospital settings. The Company’s pipeline consists of mid- to late-stage clinical assets. The Company’s most advanced clinical stage product candidate, tebipenem HBr, is in Phase 3 development, with the potential to be the first broad-spectrum oral carbapenem to treat adult patients with complicated urinary tract infections (“cUTIs”), including pyelonephritis, caused by certain microorganisms. The other programs in our pipeline are SPR206 and SPR720. SPR206 is an intravenously (“IV”) administered next generation polymyxin product candidate, for the treatment of hospital-acquired and ventilator-associated bacterial pneumonia (“HABP/VABP”) caused by MDR Gram-negative bacterial infections. In March 2025, following a reprioritization of its programs, the Company announced that it is no longer pursuing a planned Phase 2 clinical study for SPR206. SPR720 is a product candidate for first-line treatment of nontuberculous mycobacterial (“NTM”) pulmonary disease. In October 2024, the Company announced that results from a planned interim analysis of its Phase 2a clinical trial for SPR720 demonstrated the oral agent did not meet its primary endpoint, and the Company elected to suspend development of SPR720 in its oral formulation. The Company is currently completing analysis of the remaining data from all 25 patients dosed in the trial ahead of determining next steps. The Company was formed as Spero Therapeutics, LLC in December 2013 under the laws of the State of Delaware. On June 30, 2017, through a series of transactions, Spero Therapeutics, LLC merged with and into Spero Therapeutics, Inc. (formerly known as Spero OpCo, Inc.), a Delaware corporation. The Company is subject to risks and uncertainties common to companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, risks of failure or unsatisfactory results of nonclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates and the ability to secure additional capital to fund operations. The Company’s product candidates will require additional preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Since inception, the Company has funded its operations with proceeds from sales of preferred units (including bridge units, which converted into preferred units), payments received in connection with its collaboration and licensing agreements, funding from government contracts and through the sale of the Company’s common and preferred stock. The Company has incurred recurring cash outflows from operating activities and losses in most years since its inception. During the years ended December 31, 2024 and 2023, the Company had net loss of $(68.6) million and net income of $22.8 million, respectively. In addition, as of December 31, 2024, the Company had an accumulated deficit of $459.6 million. The Company expects to continue to generate operating losses for the foreseeable future. On February 25, 2025, the Company received a deficiency letter from the Listing Qualifications Department informing it that it was not in compliance with the continued listing requirements of the Nasdaq Global Select Market because the bid price for its common stock had closed below $1.00 per share for 30 consecutive business days. The Company has until August 25, 2025 to regain compliance with the bid price requirement. If the Company does not regain compliance with the bid price requirement, its common stock will be subject to delisting. Any potential delisting of the Company’s common stock could have a material adverse effect on the market for, and liquidity and price of, the Company’s common stock and would adversely affect the Company's ability to raise capital on terms acceptable to the Company, or at all. In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205- 40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. Based on the Company’s current operating plan and existing cash and cash equivalents, the Company has determined that there is substantial doubt regarding its ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. The Company will require additional funding to fund the development of its product candidates through regulatory approval and to support its continued operations. The Company will seek additional funding through public or private financings, debt financing, collaboration agreements, government grants or other venues. If our access to capital is restricted or associated borrowing costs increase as a result of developments in financial markets, our operations and financial condition could be adversely impacted. There is no assurance that the Company will be successful in obtaining sufficient funding on acceptable terms, if at all, and it could be forced to delay, reduce or eliminate some or all of its research and development programs, or product portfolio expansion efforts, which could materially adversely affect its business prospects or its ability to continue operations. The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2024

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

The Company is a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases caused by multi-drug resistant (“MDR”) bacterial infections with high unmet need. Since the Company’s inception in 2013, it has focused its efforts and financial resources on acquiring and developing product and technology rights, building our intellectual property portfolio and conducting research and development activities for its product candidates. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company believes that its novel product candidates, if successfully developed and approved, could provide meaningful benefits to patients suffering from serious rare diseases and life-threatening bacterial infections, in both the community and hospital settings. The Company’s pipeline consists of mid- to late-stage clinical assets.

The Company’s most advanced clinical stage product candidate, tebipenem HBr, is in Phase 3 development, with the potential to be the first broad-spectrum oral carbapenem to treat adult patients with complicated urinary tract infections (“cUTIs”), including pyelonephritis, caused by certain microorganisms. The other programs in our pipeline are SPR206 and SPR720. SPR206 is an intravenously (“IV”) administered next generation polymyxin product candidate, for the treatment of hospital-acquired and ventilator-associated bacterial pneumonia (“HABP/VABP”) caused by MDR Gram-negative bacterial infections. In March 2025, following a reprioritization of its programs, the Company announced that it is no longer pursuing a planned Phase 2 clinical study for SPR206. SPR720 is a product candidate for first-line treatment of nontuberculous mycobacterial (“NTM”) pulmonary disease. In October 2024, the Company announced that results from a planned interim analysis of its Phase 2a clinical trial for SPR720 demonstrated the oral agent did not meet its primary endpoint, and the Company elected to suspend development of SPR720 in its oral formulation. The Company is currently completing analysis of the remaining data from all 25 patients dosed in the trial ahead of determining next steps.

The Company was formed as Spero Therapeutics, LLC in December 2013 under the laws of the State of Delaware. On June 30, 2017, through a series of transactions, Spero Therapeutics, LLC merged with and into Spero Therapeutics, Inc. (formerly known as Spero OpCo, Inc.), a Delaware corporation.

The Company is subject to risks and uncertainties common to companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, risks of failure or unsatisfactory results of nonclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates and the ability to secure additional capital to fund operations. The Company’s product candidates will require additional preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Since inception, the Company has funded its operations with proceeds from sales of preferred units (including bridge units, which converted into preferred units), payments received in connection with its collaboration and licensing agreements, funding from government contracts and through the sale of the Company’s common and preferred stock. The Company has incurred recurring cash outflows from operating activities and losses in most years since its inception. During the years ended December 31, 2024 and 2023, the Company had net loss of $(68.6) million and net income of $22.8 million, respectively. In addition, as of December 31, 2024, the Company had an accumulated deficit of $459.6 million. The Company expects to continue to generate operating losses for the foreseeable future.

On February 25, 2025, the Company received a deficiency letter from the Listing Qualifications Department informing it that it was not in compliance with the continued listing requirements of the Nasdaq Global Select Market because the bid price for its common stock had closed below $1.00 per share for 30 consecutive business days. The Company has until August 25, 2025 to regain compliance with the bid price requirement. If the Company does not regain compliance with the bid price requirement, its common stock will be subject to delisting. Any potential delisting of the Company’s common stock could have a material adverse effect on the market for, and liquidity and price of, the Company’s common stock and would adversely affect the Company's ability to raise capital on terms acceptable to the Company, or at all.

In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205- 40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. Based on the Company’s current operating plan and existing cash and cash equivalents, the Company has determined that there is substantial doubt regarding its ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. The Company will require additional funding to fund the development of its product candidates through regulatory approval and to support its continued operations. The Company will seek additional funding through public or private financings, debt financing, collaboration agreements, government grants or other venues. If our access to capital is restricted or associated borrowing costs increase as a result of developments in financial markets, our operations and financial condition could be adversely impacted. There is no assurance that the Company will be successful in obtaining sufficient funding on acceptable terms, if at all, and it could be forced to delay, reduce or eliminate some or all of its research and development programs, or product portfolio expansion efforts, which could materially adversely affect its business prospects or its ability to continue operations.

The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.