Biogen's MS drug Zinbryta tied to more serious side effects than Avonex: Advera

Biogen's newly approved, once-monthly MS drug Zinbryta comes with more serious side effects than predecessor Avonex. But the med is safer than a competing treatment from Sanofi ($SNY), according to a recent analysis.

Healthcare analytics firm Advera Health Analytics compared study results for Zinbryta and Avonex and found that the rate of serious side effects was slightly higher for Zinbryta. The new drug, approved by the FDA on Friday, had a 24% rate of serious side effects, versus 21% for Avonex.

The drug has an efficacy edge, however. It's better than Avonex at reducing annual relapse rates and the average number of brain lesions in patients. Zinbryta’s main side effects were tied to skin and subcutaneous disorders including hypersensitivity, infections and infestations, autoimmune conditions and blood and lymphatic disorders.

Biogen declined to comment to FiercePharma about Advera's report. Sanofi did not respond to requests for comment by press time.

There were pros and cons when comparing Zinbryta with existing MS treatments such as Biogen’s Tysabri and Sanofi’s Lemtrada, Advera said. Zinbryta carries a lower risk of autoimmune problems than Lemtrada and a less serious infection risk than Tysabri and Lemtrada. But the drug also shows a greater risk of skin/hypersensitivity reactions than both of the latter treatments, the report said.

Still, Zinbryta’s elevated risk of skin issues could be “a function of the way the drug is administered,” since it’s an injection, not an infusion, Advera’s chief product officer, Robert Kyle, told FiercePharma. “Overall, Zinbryta is looking safer than (Tysabri and Lemtrada),” Kyle said.

After its FDA approval in relapsed MS last week, Biogen is preparing to launch Zinbryta in September, and analysts are forecasting sales of $447 million by 2022. Biogen is counting on that revenue to offset competition from new rivals, including a forthcoming med from Roche ($RHHBY).

Zinbryta's approval came with a black box, though, which could spell trouble for Biogen further down the line. The black box cautions against "severe liver injury, including life-threatening and fatal events" associated with the med, the FDA said in a statement. Regulators are also warning of increased risk of immune conditions, skin reactions and enlarged lymph nodes linked to the drug.

One analyst sees Zinbryta's safety profile as hampering its potential. Serious safety and tolerability issues will make the drug more of a niche product for patients at high risk for PML and others who have already failed other treatments, Leerink analyst Geoffrey Porges wrote earlier this year in a note to clients.

- here’s the full report

- read the FDA's statement 

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