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Important Note

The following information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist or other healthcare professional. It should not be construed to indicate that use of the drug is safe, appropriate, or effective for you. Consult your healthcare professional before using this drug.



COMMON BRAND NAME(S): Hiprex, Mandelamine, Urex


This medication is an antibiotic used to treat infection of the urinary tract (kidney, bladder).

How To Use

Take this medication exactly as prescribed. Take with food to prevent stomach upset. Drink plenty of fluids while taking this medication. Cranberry juice or taking vitamin C supplements may be recommended since they acidify the urine and make the drug more effective. Large amounts of milk products or antacids should be avoided. Shake the liquid form of this medication well before pouring each dose. Antibiotics work best when the amount of medicine in your body is kept at a constant level. Do this by taking the medication at evenly spaced intervals throughout the day and night. Continue to take this medication until the full prescribed amount is finished even if symptoms disappear after a few days. Stopping the medication too early may allow bacteria to continue to grow and may result in a relapse of the infection.

Side Effects

This medication may cause stomach upset, loss of appetite, diarrhea, nausea, or headache. If these symptoms persist or worsen, inform your doctor. Notify your doctor if you develop: skin rash, hives, difficulty breathing, painful urination, blood in the urine, mouth sores. If you notice other effects not listed above, contact your doctor or pharmacist.


Tell your doctor your medical history, especially: kidney or liver disease, any allergies. Methenamine should be used only when clearly needed during pregnancy. Discuss the risks and benefits with your doctor. Methenamine is excreted into breast milk. Though there have been no reports (to date) of harm to nursing infants, consult your doctor before breast-feeding.

Drug Interactions

Tell your doctor of all prescription and nonprescription medications you use, especially: sulfamethizole, antacids (e.g., bicarbonate), other urine alkalinizers (e.g., acetazolamide). Do not start or stop any medicine without doctor or pharmacist approval.


If overdose is suspected, contact your local poison control center or emergency room immediately.


This medication has been prescribed for your current condition only. Do not use it later for another infection or give it to someone else. A different medication may be needed in those cases.

Missed Dose

If you miss a dose, take it as soon as remembered. If, however, it is almost time for the next dose and the dose is two daily, take the missed dose and the next dose 5 to 6 hours apart. If the dose is 3 daily, take the missed dose and the next dose 2 to 4 hours apart. Then resume your usual dosing schedule. Do not double the dose to catch up.


Store at room temperature away from moisture and sunlight. Do not freeze liquid forms of this medication. Do not store in the bathroom.