Methenamine

What is methenamine used for?

• Methenamine is used to treat or prevent a urinary tract infection (UTI).

Before taking methenamine, tell your doctor:

• If you are allergic to methenamine; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
• If you have any of these health problems: Fluid loss (dehydrated), kidney disease or liver disease.
• If you are taking a sulfa (sulfonamide) drug. Ask your doctor if you are not sure if any of your drugs are a sulfa drug.

This is not a list of all drugs or health problems that interact with methenamine.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take methenamine with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take methenamine?

• Tell all of your health care providers that you take methenamine. This includes your doctors, nurses, pharmacists, and dentists.
• Have blood work checked as you have been told by the doctor. Talk with the doctor.
• If you are allergic to tartrazine, talk with your doctor. Some products have tartrazine.
• You may need to check the acid content (pH) of your urine using a dipstick test.
• Talk with your doctor before you take aspirin, antacids, or drugs that raise the pH of the urine while on methenamine.
• Talk with your doctor before you eat citrus fruits, dairy products, and some vegetables while taking methenamine.
• This medicine may affect certain lab tests. Tell all of your health care providers and lab workers that you take methenamine.
• Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using methenamine while you are pregnant.
• Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

How is methenamine best taken?

Use methenamine as ordered by your doctor. Read all information given to you. Follow all instructions closely.

• Keep using methenamine as you have been told by your doctor or other health care provider, even if you feel well.
• Take with or without food.

What do I do if I miss a dose?

• Take a missed dose as soon as you think about it.
• If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
• Do not take 2 doses at the same time or extra doses.

What are the side effects of methenamine that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Very upset stomach or throwing up.
• Bladder pain or pain when passing urine or change in how much urine is passed.
• Blood in the urine.

What are some other side effects of methenamine?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Upset stomach.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out methenamine?

• Store at room temperature.
• Store in a dry place. Do not store in a bathroom.
• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.

Consumer information use and disclaimer

• If your symptoms or health problems do not get better or if they become worse, call your doctor.
• Do not share your drugs with others and do not take anyone else's drugs.
• Some drugs may have another patient information leaflet. Check with your pharmacist. If you have any questions about methenamine, please talk with your doctor, nurse, pharmacist, or other health care provider.
• If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

This information should not be used to decide whether or not to take methenamine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to methenamine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.