[424B5] Theriva Biologics, Inc. Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

Theriva Biologics (TOVX) filed a prospectus supplement to disclose an amendment to certain outstanding common warrants. On October 16, 2025, the company and certain holders agreed to reduce the exercise price on Existing Warrants covering up to 6,727,280 shares of common stock from $1.10 to $0.54 per share. The supplement updates the previously effective S-1 prospectus tied to the May 2025 best efforts offering. Theriva’s common stock closed at $0.84 on October 15, 2025 on the NYSE Capital Market under the symbol TOVX.

Insights

Equity capital markets analyst

Warrant repricing to $0.54 may increase exercisability; neutral impact.

Theriva Biologics reduced the exercise price on certain Existing Warrants covering up to 6,727,280 shares from $1.10 to $0.54. This type of adjustment can make exercises more feasible when market prices exceed the new strike.

The disclosed closing price was $0.84 on October 15, 2025, above the amended strike. If holders choose to exercise, cash would typically be paid upon exercise; the excerpt does not detail proceeds or timing. Actual exercise volume depends on holder decisions.

Filed pursuant to Rule 424(b)(5)

Registration No. 333-283722 

PROSPECTUS SUPPLEMENT NO. 1

(to the prospectus dated May 7, 2025)

 

Theriva Biologics, Inc.

6,727,280 Shares of Common Stock

This prospectus supplement updates, amends and supplements the prospectus contained in our Registration Statement on Form S-1, as amended, effective as of May 7, 2025 (as supplemented or amended from time to time, the “Prospectus”) (Registration No. 333-283722) relating to the offer and sale of up to 1,990,900 shares of common stock, par value $0.001 per share (the “Common Stock”), of Theriva Biologics, Inc. (the “Company”), 6,818,180 shares of Common Stock issuable upon the exercise of 6,818,180 common warrants to purchase shares of Common Stock (the “Existing Warrants”), 4,827,280 pre-funded warrants to purchase up to 4,827,280 shares of common stock, and 11,645,460 shares of Common Stock underlying the Existing Warrants and pre-funded warrants purchased by investors in a best efforts public offering that was consummated on or about May 8, 2025. This Prospectus Supplement No. 1 (the “Prospectus Supplement”) is being filed in connection with an amendment to certain of the Existing Warrants as described below under “Amendments to Existing Warrants.” Capitalized terms used in this Prospectus Supplement and not otherwise defined herein have the meanings specified in the Prospectus.

This Prospectus Supplement is not complete without the Prospectus. This Prospectus Supplement should be read in conjunction with the Prospectus, which is to be delivered with this Prospectus Supplement, and is qualified by reference thereto, except to the extent that the information in this Prospectus Supplement updates or supersedes the information contained in the Prospectus. Please keep this Prospectus Supplement with your Prospectus for future reference.

Our shares of Common Stock are listed on the NYSE Capital Market under the symbol “TOVX”. On October 15, 2025, the closing price for our shares of Common Stock on the NYSE Capital Market was $0.84 per share.

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties under the heading “Risk Factors” beginning on page 8 of the Prospectus.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Prospectus or this Prospectus Supplement. Any representation to the contrary is a criminal offense.

AMENDMENTS TO EXISTING WARRANTS

This Prospectus Supplement is being filed to disclose the following:

On October 16, 2025, we entered into an amendment with certain holders of Existing Warrants to purchase up to 6,727,280 shares of Common Stock held in the aggregate by such holders in order to amend the exercise price under such Existing Warrants from $1.10 to $0.54 per share.

The date of this Prospectus Supplement is October 16, 2025.

FAQ

What did Theriva Biologics (TOVX) change in this prospectus supplement?

It amended certain Existing Warrants, reducing the exercise price from $1.10 to $0.54 per share.

How many shares are covered by the amended TOVX warrants?

The amendment applies to Existing Warrants to purchase up to 6,727,280 shares of common stock.

When was the warrant amendment executed by Theriva Biologics?

The amendment was entered into on October 16, 2025.

What is the trading symbol and recent closing price for Theriva Biologics?

Theriva trades on the NYSE Capital Market under TOVX; the closing price was $0.84 on October 15, 2025.

Which prior registration does this supplement update for TOVX?

It updates the prospectus in the effective Form S-1 (Registration No. 333-283722) tied to a May 2025 best efforts offering.