Methenamine

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

Methenamine may also be used for reasons not mentioned in this medication guide.

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

Methenamine works best when your urine is acidic and has a low pH. You can check your pH levels at home with urine test strips bought from a pharmacy. Your doctor may sometimes test your urine to ensure 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 improve quickly. 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. Inform 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.

Use only as directed. Inform your doctor if you are taking other medicines or have other medical conditions or allergies.

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

• kidney disease;
• severe liver disease; or
• if you are dehydrated.

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.

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

Methenamine may cause serious side effects. Call your doctor right away if you have:

• increased urination;
• painful urination;
• blood in your urine; or
• swelling, shortness of breath.

Common side effects of methenamine may include:

• painful urination;
• nausea, vomiting; or
• rash, itching.

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

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

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

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

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.