WASHINGTON — Flavocoxid — an arthritis treatment marketed as an effective counter to joint inflammation — appears to cause “clinically significant liver injury” in some patients, and physicians should probably discourage their patients from taking it, says a new study and its accompanying editorial.

Drawing on the records of 877 patients followed by the national Drug-Induced Liver Injury Network, researchers publishing in the Annals of Internal Medicine cite three cases in which flavocoxid use was found to be the “very likely” cause of acute liver injury, and a fourth in which liver injury was found to be “possibly due to” flavocoxid use.

All four patients recovered their full liver function after discontinuing use of flavocoxid.

The nutritional supplement is not a regulated pharmaceutical product, even though it’s marketed under a name — Limbrel — that sounds a lot like a drug that is widely prescribed for rheumatoid arthritis.

As a “medical food product” it’s not subject to the usual FDA safety monitoring.

Flavocoxid is “an interesting therapeutic alternative to non-steroidal anti-inflammatory drugs,” write Drs. Stephan Reichenbach and Peter Juni of the University of Bern in Switzerland, in an editorial that accompanies the Annals study.

Laboratory studies suggest that flavocoxid’s plant-based bioflavenoids inhibit two enzymes implicated in the inflammatory process, and that it may act on arthritis pain and stiffness in much the same way that medications such as ibuprofen, naproxen and celecoxib do.

The authors speculated that hypersensitivity to flavocoxid’s natural ingredients may have played a role in some of the patients’ reactions. But they also noted that “unpredictable or unregulated concentrations of … polyphenolic substances” may “set the stage for toxicity.”