Can Methenamine and Vitamin C Help Prevent Urinary Tract Infections (UTIs)?

Urinary tract infections (UTIs) are common infections, especially as you age. You can easily treat most simple UTIs with antibiotics. But, for some people, the infections may become frequent. For recurrent UTIs, treatments like methenamine and vitamin C (ascorbic acid) may decrease the risk of infections.

What is methenamine?

Methenamine (Hiprex) is an antibiotic that people often use to prevent UTIs from happening in the first place. But it’s different from other antibiotics that treat active UTIs. 

Most UTI treatments kill the bacteria that are causing an infection. Methenamine decreases bacteria in the urine by producing formaldehyde in the urinary tract. This doesn’t kill the bacteria, but it prevents bacteria from growing in the urine. 

Methenamine may be effective in preventing recurrent UTIs when more common antibiotics don’t work. 

Should you take methenamine with vitamin C?

Some people take vitamin C along with methenamine. That’s because vitamin C may help make urine more acidic. And methenamine works best when your urine is acidic. In fact, it won’t form formaldehyde unless the urine pH reaches a highly acidic level. 

There’s mixed data on how effective it is. But 1 to 4 grams of vitamin C may have some benefits. It may work to enhance the effect of methenamine on decreasing bacteria in the urine.  

Does vitamin C alone prevent UTIs?

Many people use vitamin C as a supplement to prevent UTIs. But it isn’t a proven treatment. There’s limited and mixed data on vitamin C alone as an effective treatment for UTIs. 

There’s some early lab research that shows vitamin C may prevent the growth of some bacteria. But studies haven’t proven this in people yet. So experts do not recommend vitamin C to prevent or treat UTIs.

How do you use methenamine?

Methenamine is approved for long-term use in people who are at risk for recurrent UTIs. And it’s also safe for use in children over 6 years old with recurrent infections. Depending on the formulation, people typically take either 500 mg twice a day or 1,000 mg 4 times a day. There’s no specific guidance on the length of treatment, and it can vary from person to person. 

It’s important to note that methenamine is not an appropriate treatment for an active infection. That’s because it doesn’t work to kill bacteria. It works by preventing further growth of bacteria. So you’ll need more traditional antibiotics to treat an active UTI. 

Your provider will discuss your treatment options with you and determine if methenamine is a good choice for you. 

What are the benefits of methenamine?

The use of antibiotics for recurrent UTI infections presents the possible problem of antibiotic-resistant bacteria. This is often a concern with standard treatments like sulfamethoxazole/trimethoprim, ciprofloxacin, and nitrofurantoin. But with methanamine, the risk of antibiotic resistance is lower. This means you can take methenamine for longer periods of time without developing antibiotic resistance.

Are there any side effects of methenamine?

In general methenamine is safe to use. But, as with any medication, there’s a risk of side effects with methenamine. Most side effects are related to the gastrointestinal (GI) system. You can sometimes avoid this by taking the medication with food. Potential side effects from methenamine include:

• Nausea

• Vomiting

• Stomach cramps

• Diarrhea

• Loss of appetite

• Rash

Methenamine may also cause issues if you have certain underlying conditions. You should let your provider know if you have:

• Allergy to aspirin

• Liver disease (like cirrhosis)

• Kidney disease

• Gout

• Plans to become pregnant

Which antibiotics should you try before methenamine to prevent UTIs?

There are several standard medications for UTI prevention. The medication your provider recommends often depends on your medical history. Your provider will also take into account the bacteria and treatment in your previous infections and any medication allergies or potential interactions. 

Preferred treatment for UTI prevention often includes: 

• Nitrofurantoin

• Trimethoprim

• Cephalexin

If you haven’t had any success in preventing recurrent UTIs with standard treatment, methenamine might be a reasonable option to try. 

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Written by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

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