People taking bisphosphonates, used to treat osteoporosis, have only a slightly higher risk of developing an inflammatory eye reaction, such as uveitis or conjunctivitis, than those taking other kinds of osteoporosis drugs, according to a new study out of Denmark. Having an underlying rheumatic condition, like rheumatoid arthritis (RA), or a lung disease raises that risk, but it still remains small. The study appears in the March issue of the Journal of Bone and Mineral Research.

“The important thing is, this is rare but it can be a side effect. And a lot of doctors and patients aren’t aware of this,” explains Bo Abrahamsen, MD, PhD, an endocrinologist in the Department of Medicine at the Gentofte Hospital in Copenhagen and a professor of clinical data research at the University of Southern Denmark in Odense. “You are much more likely to get this side effect or event if you are someone with a pulmonary disease. You are also more likely to get it if you’ve got rheumatoid arthritis.”

Bisphosphonates are commonly used in the United States to treat osteoporosis, or bone thinning. They include alendronate (Fosamax), ibandronate (Boniva) and risedronate (Actonel, Atelvia). Other medications used to treat osteoporosis include raloxifene (Evista), a selective estrogen receptor modulator; estrogen with and without progesterone (such as Prempro, Activella and Estrace); denosumab (Prolia), a biologic; and parathyroid hormone (Forteo).

Previous studies have reached conflicting conclusions about the link between bisphosphonate use and eye issues, leaving open the issue of whether the drugs themselves or an underlying medical condition is the reason for the higher risk. For example, patients with RA have an increased risk of inflammatory eye reactions; at the same time, they are often prescribed corticosteroids for their condition, which puts them at risk for bone thinning and requires them to take osteoporosis drugs, usually a bisphosphonate.

Because a large number of people take bisphosphonates, the researchers say it is important to better understand the risks. To do that, they analyzed a database of all medications prescribed in Denmark and identified more than 88,000 patients who started osteoporosis drugs between 1997 and 2007.