• Basic Info
• Top Questions
• Clinical Info
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What is methenamine?
Methenamine is a urinary antiinfective medicine. Methenamine fights bacteria in the urine and bladder. Methenamine may be used to treat and prevent urinary tract infections. Methenamine may also be used for purposes other than those listed here.

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What is the price of this medication and similar alternatives?

This pricing information is subject to change at the sole discretion of DS Pharmacy. For the most current and up-to-date pricing information, please visit drugstore.com.

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What are the possible side effects of methenamine?

If you experience any of the following serious side effects, stop taking methenamine and seek emergency medical attention or contact your doctor immediately:

• an allergic reaction (shortness of breath; closing of the throat; swelling of the lips, face, or tongue; or hives;

• lower back or side pain;

• blood in urine; or

• increasingly painful or difficult urination.

Other, less serious side effects may be more likely to occur. Continue to take methenamine and talk to your doctor if you experience

• nausea or upset stomach;

• decreased appetite; or

• skin rash.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

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How should I take methenamine?
Take methenamine exactly as directed by your doctor. If you do not understand these instructions, ask your doctor, nurse, or pharmacist to explain them to you. Take each dose with a full glass of water. Plenty of fluid should be consumed while taking methenamine. Methenamine should be taken with food to reduce stomach upset. Do not crush or chew the enteric-coated tablets. Swallow them whole. They are specially formulated to be less irritating to the stomach. Talk to your doctor if swallowing the tablets is difficult.

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What is the most important information I should know about methenamine?
Take all of the methenamine that has been prescribed for you even if you begin to feel better. Symptoms may start to improve before the infection is completely treated. Take each dose with a full glass of water. Plenty of fluid should be consumed while taking methenamine. Your healthcare provider may recommend drinking additional water and/or certain fruit juices (e.g., cranberry, plum, prune) and increased protein in the diet while taking methenamine to ensure adequate hydration and acidity of the urine. It may also be recommended to avoid citrus fruits and juices (e.g., orange, grapefruit, lemon), milk and dairy products, and antacids during treatment with methenamine. These products may decrease the effectiveness of methenamine. Follow your healthcare provider's instructions.

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What happens if I miss a dose?
Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the dose you missed and take only the next regularly scheduled dose. Do not take a double dose of this medication unless otherwise directed by your doctor.

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What other drugs will affect methenamine?
Do not take methenamine without first talking to your doctor if you are taking: a carbonic anhydrase inhibitor such as acetazolamide (Diamox), dichlorphenamide (Daranide), or methazolamide (Glauctabs, MZM, Neptazane); a sulfa product such as sulfadiazine, sulfamethoxazole (Bactrim, Septra, others), sulfasalazine (Azulfidine), and others; a diuretic (water pill); or a product that contains aluminum, calcium, magnesium, sodium bicarbonate, potassium or sodium citrate, or citric acid (such as antacids, vitamin or mineral pills, urinary alkalinizers, and other medications).

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Can I take this if I am pregnant or trying to get pregnant or if I am breastfeeding?

Methenamine has been assigned to pregnancy category C by the FDA. Animal studies have not been reported. It is known to cross the placenta. Two studies of methenamine use during pregnancy have not reported an increase adverse fetal outcome when compared to controls. Methenamine should only be given during pregnancy when benefit outweighs risk.

The Collaborative Perinatal Project reported 49 pregnancies involving first-trimester exposure to methenamine. Birth defects were reported in 4 infants. In 299 pregnancies involving exposure to methenamine anytime during pregnancy, 12 malformations were reported (5.34 expected). In a review of 229,101 deliveries to Michigan Medicaid patients, 209 first-trimester exposures to methenamine were recorded and 778 exposures anytime during pregnancy. A total of 8 birth defects were reported with first-trimester exposure (8 expected) and included (observed/expected) one cardiovascular defect, one oral clefts, one polydactyly, and one limb reduction.

Methenamine is excreted into human milk. The manufacturer recommends that caution be used when administering methenamine to nursing women.

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Who should NOT use this medication?

• Known hypersensitivity to the drug.
• Renal insufficiency.
• Severe hepatic insufficiency or severe dehydration.

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What does my medication look like?
Methenamine is available with a prescription under the brand names Hiprex, Urex, and Mandelamine. Other brand or generic formulations may also be available. Ask your pharmacist any questions you have about this medication, especially if it is new to you.

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What happens if I overdose?
Seek emergency medical attention if an overdose is suspected. Symptoms of a methenamine overdose are not known.

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What should I discuss with my healthcare provider before taking methenamine?
Before taking methenamine, talk to your doctor if you have liver problems; have kidney problems; have other medical conditions; or take other medications. You may not be able to take methenamine, or you may require a dosage adjustment or special monitoring during treatment. Methenamine is in the FDA pregnancy category C. This means that it is not known whether it will be harmful to an unborn baby. Do not take methenamine without first talking to your doctor if you are pregnant or could become pregnant during treatment.

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Can I stop taking the medication if I feel better?
If you have been diagnosed with a disease for which an antibiotic is needed, you must complete the prescribed course of treatment. Even if you start to feel better, do not skip any doses and remember to take the medication until it is all gone.

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I am on so many medications; do I have to take them all?
This is called polypharmacy—many different medications being used at the same time by one person. Sometimes, being on multiple medications is acceptable and appropriate but at other times it may be problematic. If you are receiving your medications from multiple physicians you need to ensure that they all know what medications you are taking. The best way to do this is to make a list of all the medications you are currently using, including all nutritional supplements, homeopathic remedies, vitamins and over-the-counter drugs (if possible, also include all the diseases you have been diagnosed with). Give a copy to every doctor who takes care of you so they have it on file, this way they can avoid duplicating medications and perhaps even try to consolidate some. After every doctor's visit remember to update the list accordingly. Also, as much as you possibly can, try to use the same pharmacy to fill all your prescriptions, this way any potential drug interactions can be caught and averted.

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Where can I get more information?
More Information

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