Ireland-based drugmaker Horizon Therapeutics USA Inc. is facing U.S. lawsuits from patients who claim its thyroid eye disease drug, Tepezza, caused them to develop permanent hearing loss or tinnitus. 

Tepezza, generically known as teprotumumab-trbw, is the first prescription drug approved by the U.S. Food and Drug Administration to treat thyroid eye disease. Thyroid eye disease is an autoimmune condition that causes swollen, red eyes and leads to double vision and eye bulging. 

The drugmaker “knew or should have known that Tepezza, when used as prescribed and intended, causes harmful hearing loss and other symptoms, including tinnitus,” according to one of the first Tepezza lawsuits filed by Daniel Weibel in August 2022 against Horizon Pharmaceuticals Inc. 

Despite numerous patient reports and scientific studies linking the drug to hearing loss and tinnitus, the drugmaker failed to warn doctors and patients about the risk, Weibel’s complaint alleges. 

The drug’s label contains warnings and precautions for Tepezza side effects, including infusion reactions, exacerbation of preexisting irritable bowel disease and hyperglycemia, but doesn’t specifically address hearing loss or tinnitus. 

Lawsuits also allege that Horizon aggressively marketed Tepezza without warning of these risks. 

In 2021, the drugmaker made $3.23 billion in drug sales.

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Tepezza-Induced Hearing Loss, Tinnitus Cited in Study

In February 2022, Horizon addressed hearing-related side effect concerns in a press release. 

“Among the thousands of patients included in this 19-month analysis (Jan. 2020 – Aug. 2021), approximately 10% of all cases reported to the safety database have included a hearing-related event,” the release read. “Adverse events experienced in the clinical trials were manageable, with few discontinuations or therapy interruptions.” 

Horizon has given the impression that hearing loss side effects have been mostly mild and reversible, lawsuits said.  

However, one February 2022 study published in American Journal of Ophthalmology found the rate of hearing problems could be as high as 81.5%. In the study, 22 out of 27 patients developed new hearing problems. Some of these patients continued to experience hearing loss after stopping treatment. 

In an April 2022 BMJ Case Reports study, a woman developed tinnitus after her third dose and hearing loss after her fifth dose. Her doctors stopped treatment, but after six weeks symptoms hadn’t improved.

Horizon Files Motion to Dismiss Lawsuit

On Oct. 25, Horizon filed a motion to dismiss Weibel’s Tepezza hearing loss lawsuit. The drugmaker claims Weibel failed to establish that the drugmaker could have changed the drug’s label without FDA approval. The company also stated that the plaintiff’s failure-to-warn claims are preempted by federal law. 

“Simply put, the complaint does not allege facts sufficient to render his negligent warnings and design claims plausible” under case law, Horizon’s lawyers stated in the motion to dismiss. 

Tepezza litigation is still in the early stages, and lawyers expect many more people to file lawsuits in the coming weeks and months.