Sodium phosphate enemas, which are commonly used to relieve constipation, can cause kidney failure and even death in elderly individuals, a new study finds.

Researchers from Israel’s Rabin Medical Center in Petah-Tikva studied a group of 11 patients who suffered from kidney failure or death after receiving enemas containing sodium phosphate. Investigators said the amount of sodium in the solution could overwhelm the kidneys of elderly people who often have chronic kidney disease, especially those who don’t drink enough water.

Researcher Yaacov Ori, M.D., told Reuters that enemas containing sodium phosphate should be avoided in high-risk individuals, such as nursing home residents with a tendency toward atonic bowel, those taking medications with anti-cholinergic effects, individuals with colitis and patients with renal failure.

The study was published in the Archives of Internal Medicine.