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More than one dose a day of popular laxatives used to treat constipation could have dangerous — even deadly — side effects for adults and children, federal health officials warned Wednesday.

Too much of over-the-counter drugs that contain sodium phosphate, such as Fleet brand enemas and oral laxatives and other similar products, could cause serious kidney and heart problems, Food and Drug Administration officials said.

The FDA has received reports of severe dehydration and changes in levels of electrolytes in the blood of people who took more than the recommended dose of the products, or more than one dose a day.

Those most at risk include young children and people older than 55, as well as people who are already dehydrated, those who have kidney disease, bowel obstructions or bowel inflammation and patients taking other medications that affect kidney function. Those include diuretics or water pills, drugs to treat high blood pressure and popular pain relievers such as aspirin, ibuprofen and naproxen.

Caregivers should not give the laxatives to kids aged 5 and younger without talking to a health care provider. And health care providers should be leery of giving oral doses of the products to kids 5 and younger. Enema versions of the drugs should never be given to children younger than 2, the FDA said.