Spero narrows Q1 loss as cash reaches $56.1M

Spero Therapeutics reported first quarter 2026 results and updated progress on its tebipenem HBr antibiotic program.

Rhea-AI Filing Summary

Spero Therapeutics reported first quarter 2026 results and updated progress on its tebipenem HBr antibiotic program. Revenue was $258,000, down from $5.874 million a year earlier, reflecting lower grant and collaboration revenue. Operating expenses fell sharply to $7.796 million from $20.605 million, leading to a narrower net loss of $7.203 million versus $13.866 million in 2025. Cash and cash equivalents increased to $56.129 million at March 31, 2026, compared with $40.265 million at year-end 2025, and the company estimates this will fund operations into 2028. Management highlighted continued work with GSK on tebipenem HBr for complicated urinary tract infections and noted an FDA PDUFA decision date of June 18, 2026, which could determine whether tebipenem HBr becomes the first oral carbapenem antibiotic for U.S. cUTI patients.

Insights

Biopharma earnings analyst

Lower revenue but reduced spending narrows losses ahead of an FDA decision.

Spero Therapeutics posted Q1 2026 revenue of $258,000, down sharply from $5.874 million on reduced grant and collaboration income. However, research and development plus general and administrative costs declined significantly, cutting the operating loss to $7.538 million.

Net loss improved to $7.203 million from $13.866 million, while cash and cash equivalents rose to $56.129 million. The company states this cash should fund operations into 2028, providing runway through the tebipenem HBr regulatory milestone.

The key dependency is the FDA’s PDUFA date for tebipenem HBr on June 18, 2026. Outcomes around this decision, and any subsequent launch activity under GSK’s lead, will shape future revenue and spending patterns.

8-K Event Classification

2 items: 2.02, 9.01

2 items

Item 2.02 Results of Operations and Financial Condition Financial

Disclosure of earnings results, typically an earnings press release or preliminary financials.

Item 9.01 Financial Statements and Exhibits Exhibits

Financial statements, pro forma financial information, or exhibit attachments filed with this report.

Key Figures

Cash and cash equivalents: $56.129 million Cash and cash equivalents prior period: $40.265 million Total revenue: $258,000 +5 more

8 metrics

Cash and cash equivalents $56.129 million As of March 31, 2026

Cash and cash equivalents prior period $40.265 million As of December 31, 2025

Total revenue $258,000 Three months ended March 31, 2026

Total revenue prior year $5.874 million Three months ended March 31, 2025

Net loss $7.203 million Three months ended March 31, 2026

Net loss prior year $13.866 million Three months ended March 31, 2025

Total operating expenses $7.796 million Three months ended March 31, 2026

Tebipenem HBr PDUFA date June 18, 2026 FDA decision date for cUTI indication

Key Terms

PDUFA date, tebipenem HBr, complicated urinary tract infections, collaboration revenue - related party, +2 more

6 terms

PDUFA date regulatory

"the anticipated PDUFA date set by the FDA as June 18, 2026"

PDUFA date is the deadline the U.S. Food and Drug Administration sets to complete its review of a drug or biologic application and decide whether to approve it. Investors watch it like a court verdict date: the decision can unlock sales and growth if approved or sharply reduce expected value if denied, so markets often move significantly as the date approaches or when the outcome is announced.

tebipenem HBr medical

"We continue to make solid progress on the tebipenem HBr program"

complicated urinary tract infections medical

"being developed for the treatment of cUTI, including pyelonephritis"

Complicated urinary tract infections are bladder or kidney infections that occur in people with underlying problems—like abnormal anatomy, medical devices, or other illnesses—that make the infection harder to treat and more likely to need hospital care. For investors, these infections matter because they often require stronger or longer courses of medicine, carry higher risks of drug resistance and expensive hospital stays, and therefore represent a larger, more urgent market for new diagnostics and therapies (think of treating a clogged, damaged pipe versus a simple leak).

collaboration revenue - related party financial

"Collaboration revenue - related party | | | 258 | | | | 5,099"

restructuring financial

"Restructuring | | | — | | | | 175"

Restructuring is a deliberate rearrangement of a company’s operations, finances, or ownership—like reorganizing a cluttered house to run more efficiently—often involving cost cuts, asset sales, debt changes, or staff moves. Investors pay attention because restructuring can improve profitability and free up cash, but it can also signal distress, incur one-time costs, or dilute shareholder value; its success affects future earnings and stock performance.

forward-looking statements regulatory

"This press release contains forward-looking statements within the meaning"

Forward-looking statements are predictions or plans that companies share about what they expect to happen in the future, like estimating sales or profits. They matter because they help investors understand a company's outlook, but since they are based on guesses and assumptions, they can sometimes be wrong.

Earnings Snapshot

Revenue: $258,000 · Guidance included

Q1 2026

Revenue $258,000 -$5.616M YoY

Net loss $7.203 million +$6.663M YoY

Cash and cash equivalents $56.129 million +$15.864M vs Dec 31, 2025

Guidance

Spero estimates its cash and cash equivalents as of March 31, 2026 will be sufficient to fund operations into 2028.

FAQ

How did Spero Therapeutics (SPRO) perform financially in Q1 2026?

Spero reported Q1 2026 revenue of $258,000, down from $5.874 million a year earlier. Net loss improved to $7.203 million from $13.866 million as operating expenses declined, narrowing losses despite the steep revenue reduction.

What is Spero Therapeutics’ cash position and runway after Q1 2026?

At March 31, 2026, Spero held $56.129 million in cash and cash equivalents, up from $40.265 million at December 31, 2025. The company estimates these resources will be sufficient to fund operations into 2028, covering key upcoming milestones.

What is the status of Spero Therapeutics’ tebipenem HBr program with GSK?

Spero continues advancing tebipenem HBr for complicated urinary tract infections with partner GSK. Tebipenem HBr is an investigational oral carbapenem antibiotic, and GSK holds an exclusive license to commercialize it in most territories, supporting late-stage development and potential launch.

When is the FDA decision expected for Spero’s tebipenem HBr in cUTI?

Spero states that the FDA’s PDUFA date for tebipenem HBr is set for June 18, 2026. This decision will determine whether the drug is approved for complicated urinary tract infections, including pyelonephritis, in U.S. patients.

How did Spero Therapeutics’ operating expenses change in Q1 2026?

Total operating expenses fell to $7.796 million in Q1 2026 from $20.605 million in Q1 2025. Research and development dropped to $2.909 million and general and administrative costs to $4.887 million, reflecting a substantial reduction in spending.

What happened to Spero Therapeutics’ collaboration and grant revenues year over year?

Grant revenue declined from $763,000 in Q1 2025 to $0 in Q1 2026. Related-party collaboration revenue decreased from $5.099 million to $258,000, and other collaboration revenue fell from $12,000 to $0, driving the overall revenue reduction.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/13/2026 - 04:02 PM Learn about SEC filing dates

false 0001701108 0001701108 2026-05-13 2026-05-13

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 13, 2026

SPERO THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Delaware		001-38266		46-4590683
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)
675 Massachusetts Avenue, 14th Floor
Cambridge, Massachusetts				02139
(Address of principal executive offices)				(Zip Code)

Registrant’s telephone number, including area code (857) 242-1600

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		SPRO		The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On May 13, 2026, Spero Therapeutics, Inc. (the “Company”) issued a press release announcing its results for the first quarter ended March 31, 2026. A copy of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information contained in this Item 2.02 and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing.

Item 9.01 Financial Statements and Exhibits

(d) Exhibits

Exhibit No.		Description
99.1		Press release issued by Spero Therapeutics, Inc. on May 13, 2026
104		Cover Page Interactive Data File (embedded within the Inline XBRL document and incorporated as Exhibit 101)

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: May 13, 2026				SPERO THERAPEUTICS, INC.
				By:		/s/ Esther Rajavelu
						Esther Rajavelu
						Chief Executive Officer, Chief Financial Officer and Chief Business Officer

Exhibit 99.1

Spero Therapeutics Announces First Quarter 2026 Operating Results and Provides Business Update

• New Drug Application (NDA) for tebipenem HBr for complicated urinary tract infections (cUTI), including pyelonephritis, is under review at the FDA, with PDUFA date of June 18, 2026

• Spero maintains its cash runway guidance into 2028

CAMBRIDGE, Mass., May 13, 2026 — Spero Therapeutics, Inc. (Nasdaq: SPRO), a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases with high unmet need, today announced financial results for the first quarter ended March 31, 2026, and provided a business update.

“We continue to make solid progress on the tebipenem HBr program alongside our licensing partner, GSK, as we prepare for the FDA’s decision expected in June,” said Esther Rajavelu, President and CEO of Spero Therapeutics. “With GSK’s leadership in anti-infectives, tebipenem HBr, if approved, has the potential to meaningfully improve treatment options for cUTI patients. Looking ahead, we are positioning the company for the next phase by advancing other corporate activities, including exploring opportunities to grow our portfolio of clinical-stage product candidates.”

Program Update

Tebipenem HBr

Tebipenem HBr is an investigational oral carbapenem antibiotic being developed for the treatment of cUTI, including pyelonephritis, to provide an effective oral therapeutic alternative to IV carbapenems. Spero granted GSK an exclusive license to commercialize tebipenem HBr in all territories, except certain Asian territories where Meiji holds development and commercialization rights.

• In February 2026, GSK announced that the U.S. Food and Drug Association (FDA) set the Prescription Drug User Fee Act (PDUFA) date to complete the review of the tebipenem HBr NDA as June 18, 2026. The NDA was submitted by GSK in December 2025, supported by results from the Phase 3 PIVOT-PO trial. The trial was stopped early for efficacy in May 2025, demonstrating non-inferiority of tebipenem HBr compared to intravenous imipenem-cilastatin in hospitalized patients with cUTI, including pyelonephritis, based on the overall response (composite of clinical cure plus microbiological eradication of the bacteria causing the infection) at the test of cure visit.

• The safety and tolerability profile of tebipenem HBr in PIVOT-PO was consistent with results reported in other studies with tebipenem and in line with that of the carbapenem antibiotic class. The most frequently reported adverse events were diarrhea and headache; these events were all mild or moderate and non-serious.

• For more information on the PIVOT-PO trial, please refer to ClinicalTrials.gov ID NCT06059846.

First Quarter 2026 Financial Results

• Spero reported a net loss of $7.2 million for the first quarter of 2026 compared to a net loss of $13.9 million for the first quarter of 2025, or a diluted net loss per share of common stock of $0.13 and $0.25, respectively.

• Total revenue for the first quarter of 2026 was $0.3 million, compared to total revenue of $5.9 million for the first quarter of 2025.

• Research and development expenses for the first quarter of 2026 were $2.9 million, compared to $13.6 million of research and development expenses for the same period in 2025. The decrease was a result of decreased clinical activities related to our pivotal Phase 3 clinical trial of tebipenem HBr, which was stopped early for efficacy during the first half of 2025, and a decrease in personnel-related costs.

• General and administrative expenses for the first quarter of 2026 were $4.9 million, compared to $6.8 million of general and administrative expenses for the same period in 2025. The decrease was a result of decreased legal and personnel-related costs.

• As of March 31, 2026, cash and cash equivalents were $56.1 million.

• Spero maintains its cash runway guidance into 2028.

For further details on Spero’s financials, refer to Spero’s Quarterly Report on Form 10-Q, filed with the U.S. Securities and Exchange Commission (SEC) today.

Government Agency Research Support

The views expressed in this press release are those of the authors and may not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.

Tebipenem HBr Research Support

Select tebipenem HBr studies have been funded in part with federal funds from the Department of Health and Human Services; Administration for Strategic Preparedness and Response; and Biomedical Advanced Research and Development Authority, under contract number HHSO100201800015C.

About Spero Therapeutics

Spero Therapeutics, headquartered in Cambridge, Massachusetts, is a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases with high unmet need. For more information, visit www.sperotherapeutics.com.

Forward Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, without limitation, statements regarding the potential for tebipenem HBr to meaningfully improve treatment options for cUTI patients, if approved; the anticipated PDUFA date set by the FDA as June 18, 2026; Spero’s exploration of opportunities to expand its portfolio of clinical stage product candidates; the potential of tebipenem HBr to be the first oral carbapenem antibiotic for US patients with cUTI, including pyelonephritis, and to set a new standard of care; the potential receipt of milestone payments under Spero’s license and collaboration agreements; Spero’s estimation that its cash and cash equivalents as of March 31, 2026 will be sufficient to fund operations into 2028; and the potential benefits of any of Spero’s current or future product candidates in treating patients. In some cases, forward-looking statements may be identified by terms such as “may,” “will,” “should,” “expect,” “plan,” “aim,” “anticipate,” “could,” “intent,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue,” the negative of these terms or other similar expressions. Any forward-looking statements in this press release are based on management’s current expectations and beliefs and are subject to a number of important risks, uncertainties and other factors that may cause actual results to differ materially from those indicated by such forward looking statements, including whether the FDA will ultimately approve tebipenem HBr and, if so, the timing of any such approval, taking into account the effects of possible regulatory delays; whether the FDA will require any additional clinical data or place labeling restrictions on the use of tebipenem HBr that would delay approval and/or reduce the commercial prospects of tebipenem HBr; whether a successful commercial launch can be achieved and market acceptance of tebipenem HBr can be established; Spero’s reliance on third parties to manufacture, develop, and commercialize its product candidates, if approved; Spero’s reliance on GSK, pursuant to the exclusive GSK License Agreement, to advance development of tebipenem HBr and GSK’s right thereunder to determine, in its sole discretion, whether to further develop and commercialize tebipenem HBr; Spero’s need for additional funding; Spero’s ability to retain key personnel; whether Spero’s cash resources will be sufficient to fund its continuing operations for the periods anticipated; and other factors discussed in the “Risk Factors” set forth in filings that Spero periodically makes with the SEC. The forward-looking statements included in this press release represent Spero’s views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Except as required by law, Spero explicitly disclaims any obligation to update any forward-looking statements.

Investor Relations Contact:

Shai Biran, PhD

Spero Therapeutics

IR@Sperotherapeutics.com

Media Inquiries:

media@sperotherapeutics.com

– Tables –

Condensed Consolidated Balance Sheet Data

(in thousands)

(unaudited)

		March 31, 2026				December 31, 2025				$ Change
Cash and cash equivalents		$	56,129			$	40,265			$	15,864
Other assets			2,892				28,654				(25,762)
Total assets		$	59,021			$	68,919			$	(9,898)
Total liabilities			6,087				9,898				(3,811)
Total stockholder’s equity			52,934				59,021				(6,087)
Total liabilities and stockholders’ equity		$	59,021			$	68,919			$	(9,898)

Spero Therapeutics, Inc.

Condensed Consolidated Statements of Operations

(in thousands, except share and per share data)

(unaudited)

		Three Months Ended March 31,
		2026				2025				$ Change
Revenues:
Grant revenue		$	—			$	763			$	(763)
Collaboration revenue - related party			258				5,099				(4,841)
Collaboration revenue			—				12				(12)
Total revenues			258				5,874				(5,616)
Operating expenses:
Research and development			2,909				13,606				(10,697)
General and administrative			4,887				6,824				(1,937)
Restructuring			—				175				(175)
Total operating expenses			7,796				20,605				(12,809)
Loss from operations			(7,538)				(14,731)				7,193
Other income (expense)			335				865				(530)
Net loss		$	(7,203)			$	(13,866)			$	6,663
Net loss per share attributable to common shareholders per share, basic and diluted		$	(0.13)			$	(0.25)			$	0.12
Weighted average shares outstanding, basic and diluted:			57,281,570				55,376,188				1,905,382

Filing Exhibits & Attachments

4 documents

Press Releases

• EX-99.1 EX-99.1 45.0 KB

Other Documents

• EX-101 XBRL TAXONOMY EXTENSION SCHEMA 3.1 KB
• EX-101 XBRL TAXONOMY EXTENSION LABEL LINKBASE 17.6 KB
• EX-101 XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE 11.0 KB