Elmiron (pentosan polysulfate sodium) can damage the retina, causing permanent vision problems if the drug has been taken at high doses and for many years. The problem is irreversible if it has been taken for 15 years or more.
Eye problems can affect up to a quarter of people who take Elmiron, an astonishing discovery for a drug that has been prescribed for decades to hundreds of thousands of people, say researchers from Kaiser Permanente in Norther California.
Damage to the retina can be reversed if drug usage has been short-term and it's realised early on that the drug is to blame for vision problems, but many assume they are developing age-related macular degeneration (AMD), and don't suspect the drug is the real culprit, the researchers say.
Ophthalmologists at Kaiser Permanente were alerted to the problem by doctors at the Emory Eye Center in Atlanta who reported that six patients on Elmiron had developed unusual changes in their macula, the central part of the retina.
The researchers found 140 patients who had taken around 5,000 Elmiron pills over 15 years—essentially one a day—and 91 of them agreed to have their eyes examined. Of those, 22 had damaged retinas, and the extent of the damage was determined by the dose and length of exposure.
Lead researcher Robin Vora advises all Elmiron users to have their eyes checked, even if they aren't suffering any vision loss. They should have a check-up every year while they're on the drug and should consider stopping it if vision starts to deteriorate.
Elmiron is the only FDA-approved drug for treating symptoms of interstitial cystitis, a bladder problem that affects around 1 million people in the US alone.