SIDE EFFECTS: Nausea, vomiting, diarrhea, abdominal cramps, uncomfortable urination, and loss of appetite may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Tell your doctor immediately if any of these unlikely but serious side effects occur: mouth sores, headache, shortness of breath, ringing in the ears, muscle cramps, body swelling.
High doses (8 or more grams daily for 3 to 4 weeks) of methenamine may cause more severe side effects, including bladder pain/irritation, frequent urination, bloody/pink urine). Tell your doctor immediately if you notice any of these symptoms.
A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching, swelling, severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
Contact your doctor for medical advice about side effects. The following numbers do not provide medical advice, but in the US you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088. In Canada, you may call Health Canada at 1-866-234-2345.
PRECAUTIONS: Before taking methenamine, tell your doctor or pharmacist if you are allergic to it; or to formaldehyde; or to tartrazine or aspirin; or if you have any other allergies.
This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: kidney problems, severe liver problems (e.g., cirrhosis, chronic hepatitis), severe dehydration.
Kidney function declines as you grow older. This medication is removed by the kidneys. Therefore, elderly people may be more sensitive to the effects of this drug.
During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.
This drug passes into breast milk. Since this medication may cause unwanted side effects in your nursing infant, consult your doctor before breast-feeding.