Business

Mirum Pharma issues USD 600m convertible notes to refinance 2029 debt, fund rare disease acquisitions

Edited by Robert McTiernan··3 min read

Foster City, California-based Mirum Pharmaceuticals (Nasdaq: MIRM) announced the pricing of USD 600 million in aggregate principal of 0.00% convertible senior notes due 2032, structured as a private placement to qualified institutional buyers. Proceeds are earmarked in part to refinance a portion of its existing 2029 convertible notes and to fund potential acquisitions aligned with its rare disease growth strategy.

The notes carry no regular interest and will not accrete, maturing on June 1, 2032. Conversion is restricted before March 1, 2032, after which time holders may convert at any time before maturity. Mirum may settle conversions in cash, common stock, or a combination at its election. The initial conversion rate is 7.1971 shares per USD 1,000 principal, implying a conversion price of approximately USD 138.94 per share — a 30% premium to the USD 106.88 closing price on May 12, 2026.

The initial purchasers, whose identities were not disclosed in the pricing announcement, hold an overallotment option to purchase up to an additional USD 90 million in principal, exercisable within 13 days of initial issuance, which would bring total gross proceeds to USD 690 million. Net proceeds are estimated at USD 583.8 million, or approximately USD 671.6 million if the overallotment is fully exercised.

Concurrent with the offering, Mirum entered into privately negotiated note exchange transactions with holders of its existing 4.00% convertible senior notes due 2029. The company expects to deploy approximately USD 475 million of net proceeds and issue approximately 3.2 million shares of common stock to retire approximately USD 237.2 million in aggregate principal of the 2029 notes. Beyond the exchange, Mirum intends to apply remaining proceeds to general corporate purposes, including potential acquisitions of complementary products, technologies, or intellectual property.

The AllSci BriefSystematic R&D and deal news. Daily.

Company overview

Mirum is a rare disease company focused on rare liver and rare genetic diseases. Its commercial portfolio includes Livmarli (maralixibat) for Alagille syndrome and progressive familial intrahepatic cholestasis, Cholbam (cholic acid) for bile-acid synthesis disorders, and Ctexli (chenodiol) for cerebrotendinous xanthomatosis.

On the pipeline side, volixibat, an IBAT inhibitor, is in late-stage development for primary sclerosing cholangitis and primary biliary cholangitis. Brelovitug, a fully human monoclonal antibody acquired through Mirum's December 2025 purchase of Bluejay Therapeutics for up to USD 820 million, is in Phase III development for chronic hepatitis delta virus and holds both FDA Breakthrough Therapy and EMA PRIME designations. Zilurgisertib, an ALK2 inhibitor for fibrodysplasia ossificans progressiva, is under FDA regulatory review. MRM-3379, a PDE4D inhibitor in-licensed from Enthorin Therapeutics and Dart Neuroscience in October 2024, is being evaluated for Fragile X syndrome, with a Phase II trial initiated in early 2026. The scale of the current convertible notes offering, combined with the concurrent 2029 note refinancing, positions Mirum to manage near-term debt obligations while retaining capital flexibility to support its expanding commercial and late-stage clinical portfolio.

This article was generated with AI assistance and reviewed and edited by the AllSci editorial team Explore more at AllSci News: https://allsci.com/news/

Spot something wrong? Report an issue with this article