Biogen Inc.’s (BIIB) bestselling multiple sclerosis drug, Tecfidera, got a label update to reflect that a possible side effect is liver injury. (See also, Biogen, Siemens Launch MS MRI Venture.)

In the recent version of the Prescribing Information leaflet, the warning section has been updated with information about a possible liver injury which may require hospitalization. The possible side effects include substantial increase in the levels of certain compounds, which can reach above permissible normal limits. The onset of the conditions can range from a few days to a few months after the start of the drug treatment.

Biogen reported that so far, only 14 instances of liver injury have came to light out of around 230,000 patients who have taken Tecfidera.

The updated label also mentions that the abnormalities got resolved when the Tecfidera treatment was discontinued by the patients, but a few cases required hospitalization. However, none of the cases led to serious conditions like liver failure, liver transplant, or death.

Impact on Tecfidera Sales?

Many multiple sclerosis drugs follow the standard practice of monitoring liver enzyme and related impacts, and the recent warning addition is not expected to lead to any serious concerns for prescribing doctors. Market experts don’t believe it will impact the drug sales.

Reuters quotes RBC Capital Markets analyst Michael Yee, who said, "There was already mention of some rare cases of elevated liver enzymes in the initial label," and “this is not going to materially change market share or future (sales) projections."

Biogen recently settled a Tecfidera patent infringement lawsuit with Danish biotech rival Forward Pharma by paying a whopping $1.25 billion. (For more, see Biogen to Pay $1.25B to Settle Patent Lawsuit.)

Tecfidera, which is one of Biogen's most successful products, clocked nearly $3 billion sales in the first nine months of 2016. With $4 billion estimated annual sales for 2016, it remains the top contributor to Biogen’s total sales. (For more, see How Does Biogen Make its Money?)

Want to learn how to invest?

Get a free 10 week email series that will teach you how to start investing.

Delivered twice a week, straight to your inbox.