Methenamine hippurate is a prescription urinary antiseptic used to help prevent recurrent urinary tract infections. It works differently from antibiotics and is mainly prescribed after an active infection has already been treated.
This medication has been available in the United States for many years and is approved for the long-term suppression or prevention of frequently recurring urinary tract infections. It is not intended to treat an active infection by itself.
Methenamine hippurate has been studied in clinical trials and reviewed in regulatory guidance to clarify how it works, when it should be used, and what precautions are important. Understanding these points helps place this medication appropriately within urinary tract infection prevention strategies.
How it works
Methenamine hippurate is classified as a urinary antiseptic. Once in the body, methenamine is converted into formaldehyde in acidic urine, and this substance has antibacterial activity. The hippurate component helps keep the urine acidic, which is necessary for the medication to work effectively.
It is active against many common bacteria that cause urinary tract infections, including Escherichia coli, enterococci, and staphylococci. Its effectiveness depends on maintaining acidic urine, so it may not work well if urine pH is too high.
Methenamine hippurate is not an antibiotic. Instead of acting throughout the body, it works locally in the urine to reduce bacterial growth and lower the risk of infection recurrence.
Indications for use
Methenamine hippurate is FDA approved for the prophylactic or suppressive treatment of frequently recurring urinary tract infections. It is used only after an acute infection has been properly treated and cleared.
It is not indicated for the treatment of an active urinary tract infection. Before starting methenamine hippurate, the current infection should be eradicated with appropriate therapy.
Dosing guidelines
The usual adult dose of methenamine hippurate is 1 gram taken by mouth twice daily. Tablets are generally taken once in the morning and once in the evening.
Pediatric dosing may differ and should follow the specific prescribing information.
The length of treatment depends on the individual situation and the frequency of recurrent infections. Methenamine hippurate may be prescribed for several months as suppressive therapy in patients who experience repeated infections.
Possible side effects
Methenamine hippurate is generally well tolerated, and most reported side effects are mild.
Common side effects include nausea, stomach upset, painful urination, and skin rash. At higher doses, bladder irritation may occur.
Serious side effects are uncommon but may include allergic reactions. If signs of a severe reaction develop, prompt medical evaluation is necessary.
Contraindications
Methenamine hippurate should not be used in people with:
- Severe renal insufficiency
- Severe hepatic insufficiency
- Severe dehydration
- Concurrent use of sulfonamide antibiotics
Caution is advised in individuals with gout or conditions that affect urine acidity. Because safe use depends on adequate kidney function, methenamine hippurate is contraindicated, rather than dose-adjusted, in significant renal impairment.
This medication should not be taken at the same time as sulfonamide antibiotics, as this combination may increase the risk of complications.
Special populations and precautions
In older adults, methenamine hippurate has been studied as an option for preventing recurrent urinary tract infections and may be considered in selected cases. However, it may be less effective in people with certain structural urinary tract abnormalities, neurogenic bladder, or long-term catheter use.
Use during pregnancy and in children should follow specific FDA labeling guidance. As with any prescription medication, the potential benefits and risks should be evaluated individually.