Gilead Sciences (GILD -0.74%) and its collaboration partner, Galapagos (GLPG -1.37%), reported somewhat disappointing news for their anti-inflammatory candidate, filgotinib. The potential blockbuster helped patients with ulcerative colitis achieve remission, but perhaps not as well as Rinvoq, a similar drug from AbbVie (ABBV -0.76%) currently approved to treat patients with rheumatoid arthritis.

Underwhelming data 

Ulcerative colitis patients who hadn't previously been treated with an injectable drug were significantly more likely to achieve remission with filgotinib than those given a placebo, but it looks like Gilead Sciences and Galapagos could have trouble competing with AbbVie for this population.

Confused businessperson.

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During a phase 2b study of Rinvoq, 10% of ulcerative colitis patients treated with 15 mg of the drug daily achieved remission compared to zero patients in the placebo group. Among a similar patient population, filgotinib helped 26.1% achieve remission compared to 15.3% of the placebo group.

Next steps?

Filgotinib and Rinvoq are both Janus kinase (JAK) inhibitors, a class of drugs associated with potentially lethal side effects experienced by an almost imperceptibly small number of clinical trial participants. At the moment, Rinvoq is approved to treat rheumatoid arthritis at a relatively limited 15 mg dosage despite appearing far more effective at higher concentrations.

If regulators take issue with the successful dosage of filgotinib for any reason, the drug's chances of approval for ulcerative colitis will fall much further. While filgotinib is arguably the safest member of the JAK inhibitor class, the lower of two doses tested didn't improve ulcerative colitis patients' chances of achieving remission.