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.

The osteoporosis drugs used in the study included alendronate, ibandronate, risedronate, raloxifene and parathyroid hormone, as well as three drugs not approved for osteoporosis in the United States, etidronate and clodronate (both bisphosphonates) and strontium ranelate.

Ninety-three percent of the patients were given a bisphosphonate (the majority received either alendronate or ibandronate), and 7 percent received a non-bisphosphonate medication (usually raloxifene).

Within a year of starting the medication, 4,769 patients (5.4 percent) filled a prescription for corticosteroid eye drops, which are prescribed for inflammatory eye conditions. Among those taking the most widely used bisphosphonate, alendronate, that figure was 5.9 percent. But patients taking alendronate also were more likely to have used a steroid eye drop the year before starting it, possibly indicating an existing problem. In fact, among those who had not used a steroid eye drop in the year before starting alendronate, only 4.4 percent received a prescription for eye medication in the year after starting the drug. “So if we only look at new uses of eye steroids, that’s around 4 percent increased risk,” Dr. Abrahamsen says.

The bottom line: Although there is a risk, the researchers say it is low and is not significantly different for those on bisphosphonates and those on other osteoporosis medications.

The researchers further found that the risk of inflammatory eye reactions was greatest among patients with pulmonary diseases or rheumatic diseases, especially those with seronegative RA and Sjögren’s syndrome, suggesting the underlying inflammatory disease is the most likely cause of the eye trouble.

Robert S. Katz, MD, a practicing rheumatologist and professor of medicine at Rush University Medical Center in Chicago, believes patients who are worried about the potential side effect of osteoporosis treatments can breathe a sigh of relief when it comes to this issue. But, he adds, if you develop eye problems while on osteoporosis drugs, you should tell your doctor and ask what course of treatment is most appropriate for you.

“The treatment of osteoporosis is extremely important. And many patients – whether taking prednisone [a corticosteroid] or not – can develop bone loss and osteoporosis,” Dr. Katz says. “Eye disease, which is rare, appears to be associated with rheumatic disease and not osteoporosis treatment. That’s reassuring. It’s one less thing to worry about.”