Generic Name: Methenamine Brand Name(s): Generics only. No brands available.

Uses

What is Methenamine used for?

Methenamine is used to prevent or control returning urinary tract infections caused by certain bacteria. It is not used to treat an active infection. Other antibiotics must be used first to treat and cure the infection. Methenamine is an antibiotic that stops the growth of bacteria in urine. This medication also contains an ingredient that helps to make the urine acidic. When the urine is acidic, methenamine turns into formaldehyde to kill the bacteria.

This antibiotic is effective only against bacterial infections in the urinary tract. It will not work for other types of bacterial infections (such as in the blood) or for viral infections (such as the common cold or flu). Unnecessary use or misuse of any antibiotic can lead to its decreased effectiveness.

How should I take Methenamine?

Take this medication by mouth as directed by your doctor. Dosage is based on the brand of methenamine you are prescribed, your medical condition, and your response to treatment. For children, dosage is also based on age and weight.

Methenamine works better if your urine is more acidic. Your doctor may test the acidity of your urine (urine pH). If necessary, your doctor may recommend ways to increase urine acidity (such as by taking vitamin C/drinking cranberry juice, limiting foods that decrease acidity/increase alkalinity such as milk products/most fruits, adjusting alkalinizing medications). See also Drug Interactions section. Follow your doctor’s instructions.

For the best effect, take this antibiotic at evenly spaced times. To help you remember, take this medication at the same time(s) every day.

Continue to take this medication for the full time prescribed, even if you feel well. Skipping doses or stopping the medication too early may allow bacteria to continue to grow, which may result in a return of the infection and make the bacteria more difficult to treat (resistant). Do not take more of this drug than directed because it may increase your chance of side effects.

Tell your doctor if symptoms of a urinary tract infection return (such as burning/painful/frequent urination).

How do I store Methenamine?

Methenamine is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Methenamine in the bathroom or the freezer. There may be different brands of Methenamine that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Methenamine down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Methenamine?

Before taking methenamine, tell your doctor or pharmacist if you are allergic to it; or to formaldehyde; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney problems, liver problems, dehydration.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This drug passes into breast milk and the effect on a nursing infant is unknown. Consult your doctor before breast-feeding.

Is it safe during pregnancy or breast-feeding?

There are no adequate studies in women for determining risk when using this Methenamine during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Methenamine. Methenamine is pregnancy risk category C according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk,
  • B=No risk in some studies,
  • C=There may be some risk,
  • D=Positive evidence of risk,
  • X=Contraindicated,
  • N=Unknown

Side effects

What side effects can occur from Methenamine?

Nausea, vomiting, diarrhea, abdominal cramps, and loss of appetite may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Painful or difficult urination may occur with methenamine, although less often. Report these side effects to your doctor, who may need to lower your dose of methenamine or change your treatment to make your urine less acidic.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Taking higher than recommended doses of methenamine may cause bladder irritation, painful/frequent urination, and bloody/pink urine. Tell your doctor right away if you have any of these symptoms.

Tell your doctor right away if any of these unlikely but serious side effects occur: mouth sores, unusual headache, ringing in the ears, muscle cramps, swelling of the arms/legs.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.

Interactions

What drugs may interact with Methenamine?

Some products that may interact with this drug include: sulfonamide drugs (including sulfa antibiotics such as sulfamethizole), products that decrease the amount of acid in the urine (urinary alkalinizers such as antacids, sodium bicarbonate, potassium or sodium citrate, carbonic anhydrase inhibitors such as acetazolamide).

This medication may interfere with certain laboratory tests, possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

Methenamine may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Does food or alcohol interact with Methenamine?

Methenamine may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Methenamine?

Methenamine may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Dosage

The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using this Methenamine.

What is the dose of Methenamine for an adult?

Usual Adult Dose for Cystitis

Hippurate: 1 g orally twice a day (morning and night)

Mandelate: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring urinary tract infections (UTIs) when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Adult Dose for Cystitis Prophylaxis

Hippurate: 1 g orally twice a day (morning and night)

Mandelate: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring urinary tract infections (UTIs) when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Adult Dose for Pyelonephritis

Hippurate: 1 g orally twice a day (morning and night)

Mandelate: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring urinary tract infections (UTIs) when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Adult Dose for Urinary Tract Infection

Hippurate: 1 g orally twice a day (morning and night)

Mandelate: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring urinary tract infections (UTIs) when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Renal Dose Adjustments

Renal dysfunction: Contraindicated

Liver Dose Adjustments

Severe liver dysfunction: Contraindicated

Dialysis

Renal dysfunction: Contraindicated

Other Comments

Administration advice:

-Hippurate: Only use after infection eradicated by other appropriate antibacterial drugs

-Restrict alkalinizing foods and drugs; antibacterial activity of this drug is greater in acid urine (maximum efficacy occurs up to pH 5.5).

-Start supplemental acidification of the urine if needed based on urinary pH and clinical response.

Storage requirements:

-Store at 25C (77F); excursions permitted to 15C to 30C (59F to 86F).

-Mandelate: Store in tight, light-resistant bottle

General:

-Mandelate: When used as recommended, this drug is especially suitable for long-term therapy due to its safety and because no resistance to formaldehyde develops; pathogens resistant to other antibacterial agents may respond to this drug.

-Mandelate prophylactic use rationale: As urine is a good culture medium for many urinary pathogens, inoculation by a few organisms (relapse or reinfection) may cause bacteriuria in susceptible patients. The rationale for managing recurring UTI (bacteriuria) is to change urine from growth-supporting to growth-inhibiting medium; data available showing long-term use of this drug can prevent bacteriuria recurrence in patients with chronic pyelonephritis.

-Mandelate therapeutic use rationale: This drug helps sterilize urine; if underlying pathologic conditions prevent sterilization by any means, it can help suppress bacteriuria. This drug should not be used alone for acute parenchymal infections causing systemic symptoms (e.g., chills, fever); thorough diagnostic investigation as a part of overall UTI management recommended with use of this drug.

Monitoring:

-Genitourinary: Urinary pH; urine cultures

-Hepatic: Liver function studies (periodically during therapy)

Patient advice:

-To ensure an acidic pH, restrict or avoid milk products and antacids containing sodium carbonate or bicarbonate.

-Avoid missing doses and complete the entire course of therapy.

What is the dose of Methenamine for a child?

Usual Pediatric Dose for Cystitis

Hippurate:

6 to 12 years: 0.5 to 1 g orally twice a day (morning and night)

13 years or older: 1 g orally twice a day (morning and night)

Mandelate:

6 to 12 years: 0.5 g orally 4 times a day (after each meal and at bedtime)

13 years or older: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring UTIs when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Pediatric Dose for Cystitis Prophylaxis

Hippurate:

6 to 12 years: 0.5 to 1 g orally twice a day (morning and night)

13 years or older: 1 g orally twice a day (morning and night)

Mandelate:

6 to 12 years: 0.5 g orally 4 times a day (after each meal and at bedtime)

13 years or older: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring UTIs when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Pediatric Dose for Pyelonephritis

Hippurate:

6 to 12 years: 0.5 to 1 g orally twice a day (morning and night)

13 years or older: 1 g orally twice a day (morning and night)

Mandelate:

6 to 12 years: 0.5 g orally 4 times a day (after each meal and at bedtime)

13 years or older: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring UTIs when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Usual Pediatric Dose for Urinary Tract Infection

Hippurate:

6 to 12 years: 0.5 to 1 g orally twice a day (morning and night)

13 years or older: 1 g orally twice a day (morning and night)

Mandelate:

6 to 12 years: 0.5 g orally 4 times a day (after each meal and at bedtime)

13 years or older: 1 g orally 4 times a day (after each meal and at bedtime)

Uses:

-Hippurate: For prophylactic or suppressive treatment of frequently recurring UTIs when long-term therapy deemed necessary

-Mandelate: For the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic UTIs; for infected residual urine due to some neurologic diseases

Precautions

Safety and efficacy have not been established in patients younger than 6 years.

How is Methenamine available?

Methenamine is available in the following dosage forms and strengths:

  • Oral tablet,
  • Oral suspension,
  • Compounding powder.

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Methenamine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

 

Hello Health Group does not provide medical advice, diagnosis or treatment.

Sources

Review Date: March 23, 2018 | Last Modified: March 23, 2018