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Generic name: methenamine [ meh-THEH-na-meen ]
Brand names: Hiprex, Mandelamine, Urex
Dosage form: oral tablet (hippurate 1 g; mandelate 0.5 g; mandelate 1 g)
Drug class: Urinary anti-infectives

Medically reviewed by on May 19, 2023. Written by Cerner Multum.

What is methenamine?

Methenamine is an antibacterial medicine used to treat or prevent bladder infections in adults and children at least 6 years old.

Methenamine may also be used for purposes not listed in this medication guide.

Methenamine side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Methenamine may cause serious side effects. Call your doctor at once if you have:

Common side effects of methenamine may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Use only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Before taking this medicine

You should not use methenamine if you are allergic to it, or if you have:

Ask a doctor or pharmacist if methenamine is safe to use if you've ever had liver problems.

Ask a doctor before using this medicine if you are pregnant.

Do not breastfeed.

How should I take methenamine?

Use exactly as directed on the label, or as prescribed by your doctor.

Methenamine works best when your urine has a low pH and is acidic. You can measure your pH levels at home using urine test strips purchased from a pharmacy. Your doctor may occasionally test your urine to make sure an infection has cleared.

Learn about the foods to eat or avoid to help keep your urine acidic. Your doctor may also prescribe other medicines. Drink plenty of liquids.

Follow your doctor's diet and medication instructions very closely.

Keep using this medicine even if your symptoms quickly improve. Skipping doses could make your infection resistant to medication. Methenamine will not treat a viral infection (flu or a common cold).

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using methenamine.

Do not use methenamine to treat any condition that has not been checked by your doctor.

Do not share this medicine with another person, even if they have the same symptoms you have.

Store at room temperature away from moisture, heat, and light. Keep the bottle tightly closed when not in use.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking methenamine?

Avoid taking extra methenamine, or you could have side effects such as bladder irritation, pain, increased urination, and blood in the urine.

What other drugs will affect methenamine?

Other drugs may affect methenamine, especially a sulfa drug. Tell your doctor about all other medicines you use. This includes prescription and over-the-counter medicines, vitamins, and herbal products.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.