Trending
Dear Dr. Roach: It's well-known that formaldehyde is toxic and can be a cause of cancer. Hiprex, which I've been taking for a few years, works by turning into an antiseptic called formaldehyde in the urinary tract to prevent bacteria from growing. Should I be concerned? I haven't read any studies saying that it's harmful to be taken for the long-term future. -- J.B.
Answer: You're exactly right that methenamine (Hiprex and other brand names) in acidic urine will be hydrolyzed to formaldehyde, which is an antiseptic that kills bacteria in the urine. Formaldehyde isn't an antibiotic, and methenamine isn't indicated for treating urinary tract infections; rather, it prevents them, as you correctly said.
The urine needs to be acidic for methenamine to become formaldehyde, so you need to be careful to avoid alkalinizing food with your diet. (Citrus fruits, despite being acidic themselves, promote a more-alkaline urine because the liver makes bicarbonate ion out of the citric acid, which turns the urine alkaline.) Or you can take methenamine with an organic acid, such as vitamin C or aspirin, to ensure acidic urine.
The body makes formaldehyde in large amounts daily as part of the catabolism (breakdown) of proteins and amino acids -- thousands of times larger than the amount of formaldehyde that's made in the urine by taking methenamine. Formaldehyde is, indeed, a known carcinogen when it's inhaled. It isn't clear that formaldehyde in food or water is carcinogenic.
Rats that were given large amounts of formaldehyde (according to body weight) didn't have increased cancer rates. More importantly, large studies of people taking methenamine haven't shown increased cancer rates.
Even with all this reassuring data, it's still wise to take any symptoms seriously. Blood in the urine could be due to an infection or bladder irritation. But it's also a possible sign of bladder cancer and should be taken seriously, especially in people who are at a higher risk -- such as those who are taking immunosuppressive drugs.
Readers may email questions to ToYourGoodHealth@med.cornell.edu.