Rezurock Lawsuit Claims GVHD Medication Caused Debilitating Skin Condition, Prurigo Nodularis

Prurigo nodularis treatment often includes Dupixent, which has recently faced lawsuits alleging it may cause or worsen a rare form of skin cancer known as cutaneous T-cell lymphoma.

A California man has filed a Rezurock lawsuit, alleging the medication caused him to develop a severe skin disorder that has interfered with his ability to sleep, wear normal clothing and continue working as a nurse.

The complaint (PDF) was brought by Philip Mizuno in San Joaquin County Superior Court on May 4, naming Sanofi Vaccines U.S. Inc. and Kadmon Pharmaceuticals LLC as the defendants. The case was removed to the U.S. District Court for the Eastern District of California on June 9.

Mizuno claims the drugmakers failed to adequately warn patients and physicians that side effects of Rezurock could trigger severe dermatologic reactions. 

Rezurock Skin Condition Side Effects

Rezurock (belumosudil) is a prescription medication approved to treat chronic graft-versus-host disease (GVHD), which is a serious complication that can occur after stem cell or bone marrow transplants. When the condition occurs, donor immune cells attack the recipient’s tissues and organs, potentially causing skin rashes, diarrhea and liver problems.

However, in Mizuno’s case, the medication allegedly led to the development of prurigo nodularis, a chronic skin disease characterized by intensely itchy, firm and hard nodules appearing across the body.

One potential treatment for prurigo nodularis is Dupixent, another Sanofi drug. However, Dupixent has been linked to other serious adverse side effects, including cutaneous T-cell lymphoma (CTCL), which is a rare form of non-Hodgkin’s lymphoma that primarily affects the skin.

In light of these concerns, a series of Dupixent lawsuits have been filed in recent months, alleging that the drug’s manufacturers failed to adequately investigate and disclose evidence that it may cause, accelerate or mask symptoms of rare T-cell lymphomas.

Rezurock Prurigo Nodularis Diagnosis

According to the lawsuit, Mizuno began taking Rezurock in March 2024 after discussing treatment options with his physician for long-standing GVHD symptoms. At the time, medical records indicated his skin was normal, with no rashes or lesions present.

However, within weeks of starting treatment, the complaint claims Mizuno began experiencing worsening rashes, itching and pain that he attributed to the medication. During an April 2024 counseling session, he reportedly described a significant increase in symptoms that became severe enough for him to stop taking the drug.

The lawsuit states that Mizuno’s condition continued to worsen over the following months, with physicians documenting new skin lesions associated with burning pain and persistent dermatologic symptoms.

In July 2024, a dermatologist diagnosed him with prurigo nodularis, describing numerous excoriated papules and plaques across his back, chest and arm. The complaint indicates he continued taking Rezurock while doctors attempted to treat the condition with topical medications and other therapies, yet his symptoms persisted.

Medical records cited in the lawsuit indicate Mizuno later underwent treatment with Dupixent, Nemluvio, UV light therapy and other interventions in an effort to control the disease. Physicians eventually listed belumosudil under “Allergies” for Mizuno.

The lawsuit indicates the condition became so painful that Mizuno could not lie on his back, had difficulty sitting due to pressure on the lesions and often avoided wearing clothing because it aggravated the affected areas. These factors have prevented him from working, even part time, as a nurse. 

Mizuno says he was still suffering from widespread nodules in late 2025, with one physician documenting between 20 and 100 lesions. He claims he eventually underwent liquid nitrogen treatments to remove dozens of lesions.

Rezurock Skin Reaction Warning Allegations

The filing alleges Sanofi and Kadmon knew, or should have known, that Rezurock could cause prurigo nodularis or similar severe skin reactions, yet failed to disclose that risk in prescribing information, product labeling or patient warnings.

Mizuno notes that during a pharmacist consultation before treatment began, he was warned about a number of potential side effects, including low blood counts, fatigue, diarrhea, shortness of breath, swelling, nausea and high blood pressure. However, prurigo nodularis and comparable severe skin disorders were not among the risks disclosed.

“Each defendant aided and abetted, encouraged, and rendered substantial assistance to the other defendants in breaching their obligations to Plaintiff. In taking action to aid and abet and substantially assist the commissions of these wrongful acts and other wrongdoings complained of, each defendant acted with an awareness of its primary wrongdoing and realized that its conduct would substantially assist the accomplishment of the wrongful conduct, wrongful goals, and wrongdoing.”

— Philip Mizuno v. Sanofi Vaccines U.S. Inc. et al.

The lawsuit claims adequate warnings would have allowed Mizuno and his physicians to consider alternative treatments, adjust therapy or more closely monitor for signs of severe dermatologic injury.

Mizuno raises allegations of negligence, strict product liability and breach of implied warranty. He seeks at least $500,000 in compensatory damages, as well as additional damages to be determined at trial.

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