Pfizer has been battling it out against rivals in arthritis and ulcerative colitis with its Xeljanz, and its drug has been posting big sales gains. But in a surprise disclosure, the company outlined safety concerns for a higher dose of the drug noticed by an independent board in a postmarketing study.

Pfizer said Wednesday it’s taking steps to transition (PDF) rheumatoid arthritis patients who had been taking Xeljanz 10-mg twice per day in a postmarketing study to a 5-mg dose twice daily. The company is making the change after an independent data safety monitoring board observed that patients on the 10-mg tablet had higher rates of pulmonary embolism than those in the tumor necrosis factor inhibitor control group, plus higher rates of death compared with patients on TNFi and the lower 5-mg Xeljanz dose.

Xeljanz is recommended in the 5-mg dose twice daily for patients with rheumatoid arthritis and psoriatic arthritis. The drug is recommended in the 10-mg dose twice daily for patients with ulcerative colitis for at least eight weeks, and then either strength thereafter.

The study was designed to assess the risk of cardiovascular events in RA patients 50 years of age and older with at least one risk factor. A Pfizer representative said the company will "continue to evaluate the risk benefit profile of [Xeljanz] across all indications and we will continue to work with regulators as more data become available." The company doesn't plan any further action right now, and the study data remain blinded.

Wednesday’s disclosure comes as the pharma giant counts on Xeljanz to be one of its big growth engines heading into 2019. The drug generated $1.77 billion last year, a 32% leap over 2017. The drug is a crucial component in the company’s 2019 guidance, CFO Frank D’Amelio said as Pfizer announced fourth-quarter 2018 results.

Pfizer expects to lose exclusivity for blockbuster Lyrica at the end of June, meaning other drugs will need to step up for the company to hit its 2019 guidance of $52 billion to $54 billion. In an effort to boost Xeljanz share and awareness, the company has been spending big on DTC advertising. In Janaury, the company took the No. 1 position in DTC ad spending, besting AbbVie’s Humira promotion efforts.

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