Methenamine (Oral)

Methenamine is an anti-infective that treats and prevents bacterial infections by suppressing bacteria in the urine.


Methenamine is a urinary anti-infective used to treat chronic and reoccurring urinary tract infections (UTIs) caused by bacteria when other antibiotics do not work. It is safe to use as a long-term treatment for chronic UTIs and microorganisms do not develop a resistance to it. To manage chronic or reoccurring UTIs, the urine needs to be changed from growth-supporting to growth-inhibiting, and data shows long-term use prevented bacteria in patients with chronic inflammation of the kidneys. It sterilizes the urine when other conditions prevent sterilization and help suppress bacteria. It's more effective in acidic urine with maximum efficiently at a pH of 5.5. It treats cystitis, a bladder inflammation, and pyelonephritis, a kidney infection caused by bacteria, as well as preventing bladder infections.

Studies have shown that cleansing the bladder with antimicrobial agents lowers bacteria; however, it is limited because of allergic reactions. Methenamine is a safer option, especially for long-term treatment, and well tolerated with minor side effects reported. It may lower bacteria and UTIs in patients managed by occasional catheterization; however, its long-term efficiency in decreasing reoccurring UTIs has not been demonstrated. Catheter-related UTIs are harder to treat with common antibiotics and patients should call a doctor if they experience any of these signs of UTI.

Signs of UTI

  • Abnormal color or blood in urine
  • Foul or strong odor of urine
  • Frequent urge to urinate
  • Pressure, pain, or spasms in back or stomach
  • Chills, fever, or fatigue

The doctor tests the patient's urine to determine the type of bacteria and look at red and white blood cells before they prescribe methenamine. They may also order an ultrasound or CT scan of the abdomen and tests to check liver and kidney function to make adjustments in dosage. In addition to medicine it is important to increase fluid intake to help flush bacteria out of the urinary tract; however, avoid drinks that will irritate the bladder such as alcohol, citrus juices, and caffeine. If left untreated, there is a risk of the infection spreading and having a UTI for long periods may cause stones in kidneys and bladder. It is especially important for patients using catheters to call their doctor immediately if they experience symptoms. To prevent infections, follow proper cleaning and catheter care.

Conditions Treated

  • Urinary tract infections (UTIs)
  • Cystitis
  • Pyelonephritis

Type Of Medicine

  • Urinary anti-infective

Side Effects

To avoid unwanted side effects, it is important to tell the doctor about any allergies, medical conditions, current medication, pregnant, or breastfeeding. Tell the doctor about any allergies, especially to aspirin and yellow dye to avoid allegoric reactions. Some medical conditions are affected by this medication especially liver and kidney issues, severe dehydration, and gout. Certain medicines do not interact well when combined and it is extremely important to let the doctor know what is currently being taken. This includes prescriptions, over-the-counter, and dietary supplements especially any sulpha drugs. This medicine can pass to a fetus or through breast milk and while no studies to determine effects on babies, it is still important to tell the doctor about pregnancies and nursing.

Methenamine is usually well tolerated with only minor side effects reported in 3.5% of patients. However, high doses, 8gr for a few weeks, can lead to blood and foam in urine, painful urination, and bladder irritation. Not all possible side effects have been reported therefore it is important to report any unusual or new symptoms after starting treatment. Some side effects may be worsening symptoms of existing liver and kidney diseases or not functioning properly. Report any side effects even if they do not require medical attention, and keep all appointments for the doctor and lab work to manage treatment in the long-term. The doctor testing regularly for effects on the liver and kidney functions will help to avoid these side effects.

  • Skin rash
  • Nausea or vomiting
  • Blood in urine
  • Lower back or stomach pain
  • Pain or burning during urination
  • Diarrhea or stomach cramps
  • Loss of appetite
  • Hives or itching


Methenamine works best in acid urine and is at its maximum effectiveness when pH is above 5.5. To ensure urine is at this pH, it is important to avoid dairy products and antacids with sodium carbonate or bicarbonate. The doctor may also suggest avoiding certain foods such as citrus fruits and juices or increase intake of certain foods like cranberries. Discuss any special diets with the doctor, for example, a diabetic diet or heart-healthy foods. Ask the doctor what kinds and how much fluids should be drunk to flush bacteria out. In addition to these, it is important to take doses exactly as prescribed and take with food if nausea occurs.

Follow the entire doctor's directions on the label, never take less or more than prescribed. It is important to finish out the medicine even if feeling better in order for it to effectively work. If it is not taken for the full amount of time on the label, then the UTI will not be properly treated. Taking too much can result in unwanted side effects and if a dose is missed, take it immediately unless it is close to time for another dose. Follow these directions for the form of medicine given.

Dry granule form

  • Dissolve contents in 2 to 4 ounces of cold water
  • Stir well and drink all

Liquid form

  • Use a measuring device to get proper dose
  • Average household teaspoon is not accurate
  • Mix well before use

Enteric-coated tablet form

  • Swallow tablets whole
  • Do not crush, break, or take chipped

Hippurate is used as a suppressive treatment for reoccurring UTIs when long-term treatment becomes necessary. It is only used after antibiotics have failed and works better if alkalinizing foods and medicines are avoided while taking. Mandelate is used to eliminate bacteria in the urine which causes cystitis, pyelonephritis, and other chronic ITUs. It is especially effective when long-term treatment is necessary because microorganisms cannot develop a resistance to medicine. It helps prevent bacteria in patients with chronic kidney inflammation because of bacteria.

The average dose of methenamine hippurate is taken twice a day, in the morning and at night.

  • 13 years to adults: 1gr
  • 6 to 12 years: 500mg to 1 gr
  • 6 years and younger: consult the doctor

The average dose of methenamine mandelate is taken four times a day, after each meal and before bedtime.

  • 13 years to adults: 1 gr
  • 6 to 12 years: 500mg
  • 6 years and younger: 8.3mg per pound


Methenamines can interact with other medications, especially sulfonamides or sulpha drugs. This is not a complete list of medication interactions and it is always important to tell the doctor about anything currently taking or before taking something new while on methenamine. It is helpful to have a list of medications to show the doctor including nonprescription, vitamins, herbal or other dietary supplements to avoid any dangerous reaction.

  • Acetazolamide
  • Mafenide
  • Sulfonamides
  • Vaxchora
  • Zonisamide


This medication may cause an increased chance of worsening symptoms for certain medical conditions. Patients with liver disease or function issues may experience changes even from a small amount of ammonia and formaldehyde. The doctor may need to adjust the dosage for patients with liver and kidney issues and it increases the risk of side effects or symptoms. The doctor may run tests to determine liver function before prescribing. If symptoms do not improve within a few days or they worsen, call the doctor right away.

  • Liver disease
  • Kidney disease
  • Dehydration
  • Gout

Methenamine is only for infections in the urinary tract caused by bacteria and is not meant for viral infections such as the common cold. Never take it for another type of infection because it is specifically designed to treat and prevent bacteria in the urine. Taking it with an infection not caused by bacteria is not beneficial and can cause the bacteria to become resistant to this and other antibodies. It is for treatment of bacterial UTIs only when other antibodies fail or long-term treatment is needed for chronic or recurring UTIs. Skipping doses or not taking for the full amount of time will decrease the effectiveness of treatment and increase the chance that the bacteria will develop a resistance to antibacterial medicines in the future.


Keep in a closed container away from heat, moisture, and from freezing at room temperature between 59F and 86F. The ideal temperature is 77F but can be stored at the other temperatures when necessary. Keep out of reach of children and animals by locking safety caps and immediately putting in a safe place after use. Because this medicine should all be taken, there is no need to find a take-back program or dispose of it; however, contacting the doctor, pharmacist, or local recycling depart to ask about medicine take-back programs is the best way to dispose of unused or out of date medicine. Remember, before throwing away the containers the medicine came in to scratch out all the information or mark through with a sharpie.


Methenamine is a urinary anti-infective used to treat recurring UTIs caused by bacteria and is not safe to use for a viral infection. It is prescribed after other medications did not clear up the infection and can be used by patients who are a catheter when they need long-term treatment. It cannot be mixed with sulpha drugs and antacids with sodium carbonate or bicarbonate because the urine needs to be 5.5pH for its maximum efficiency. In addition to the medicine, the doctor will recommend extra fluids and may suggest foods and liquids to avoid or increase intake of while on this medicine. If the patient is on a special diet for an exciting condition, the doctor needs to know in order to properly suggest what foods and liquids the patient should increase or avoid.

It is important to follow the dosing schedule directly and take for the full amount of time or the bacteria may develop a resistance to these types of medication. Do not take more or less then the prescribed dosage and skip any missed dose if it is almost time for next dose. The doctor needs to know about medical conditions, especially liver and kidney disease or function problems because the doctor may adjust the dosage to avoid an increased risk of symptoms from those conditions becoming worse. Depending on whether methenamine is hippurate or mandelate, the medicine is taken twice a day and four times a day respectively. The difference between them is hippurate is used for long-term treatment and mandelate is used to eliminate bacteria in the urine for long-term prevention of UTIs.