Gilead's shares slip on hepatitis C drug-interaction warning

Shares in Gilead Sciences fell as much as 2.7 percent Monday following its recent warning about a rare, but potentially fatal interaction between the antiarrhythmic therapy amiodarone and the company's hepatitis C drugs Sovaldi (sofosbuvir) or Harvoni (ledipasvir/sofosbuvir). Last week, the drugmaker informed healthcare workers of nine cases in which patients co-administered amiodarone with either Harvoni or Sovaldi experienced symptomatic bradycardia, while one of the patients died.

Gilead said that of the nine patients, six experienced bradycardia during the first day of treatment with Harvoni or Sovaldi, and pacemakers were necessary for three of the individuals. The company noted that several patients were also using other antiviral agents, with seven patients being treated with a beta blocker. The drugmaker added that the mechanism of action for the adverse interaction remains unclear.

Gilead stated that the company is "confident in the safety profiles of Sovaldi and Harvoni," adding that it will continue to monitor the safety of the drugs in coordination with health regulators and the medical community. Meanwhile, the drugmaker said concurrent use of amiodarone with Harvoni or Sovaldi is not recommended, but that if co-administration is necessary, patients should undergo close cardiac monitoring, including in-hospital observation for the first 48 hours of treatment.

Commenting on the news, a Baird analyst indicated that the situation is unlikely to have any substantial effect on the use of either hepatitis C drug, as only about 1000 of the more than 200 000 patients prescribed Harvoni or Sovaldi have also received amiodarone. Moreover, the analyst noted that amiodarone itself carries a bradycardia risk of 2.5 percent.

Sanford Bernstein analyst Geoffrey Porges concurred, stating "there is no inherent reason that hepatitis C-infected individuals should have much higher rates of treatment with amiodarone, so the exclusion of co-administration is unlikely to materially affect the dynamics of the market." Porges also suggested the news was unlikely to give any advantage to AbbVie, which markets the hepatitis C treatment regimen Viekira Pak combining Viekira (ombitasvir/paritaprevir/ritonavir) and Exviera (dasabuvir). "It's hard to make the case that AbbVie's drug is any safer for the few [hepatitis C] patients taking amiodarone than Sovaldi/Harvoni," he said.

Gilead reported last month that Harvoni generated $2.1 billion in revenue for the quarter ended December 31, while sales of Sovaldi totalled $1.7 billion.

For further analysis, see ViewPoints: Analysts downplay the impact of safety signal for Gilead’s HCV drugs.

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