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).
You may not be able to take methenamine, or you may require a dosage
adjustment or special monitoring during treatment if you are taking any of the medicines listed
above.
Drugs other than those listed here may also interact with methenamine. Talk to your doctor
and pharmacist before taking any prescription or over-the-counter medicines, including vitamins,
minerals, and herbal products.
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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