Methenamine Side Effects
Not all side effects for methenamine may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.
For the Consumer
Applies to methenamine: oral suspension, oral tablet, oral tablet enteric coated
In addition to its needed effects, some unwanted effects may be caused by methenamine. In the event that any of these side effects do occur, they may require medical attention.
You should check with your doctor immediately if any of these side effects occur when taking methenamine:Less common
- Skin rash
- Blood in urine
- lower back pain
- pain or burning while urinating
Some of the side effects that can occur with methenamine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:Less common
- Nausea and vomiting
For Healthcare Professionals
Applies to methenamine: compounding powder, oral suspension, oral tablet
Methenamine is generally well tolerated. Minor side effects have been reported in less than 3.5% of patients.
Dermatologic side effects have included rash and pruritus.
Gastrointestinal side effects have included nausea, vomiting, diarrhea, anorexia, and abdominal cramping.
Genitourinary side effects have included dysuria, hematuria, and urinary frequency. High doses have been associated with albuminuria, gross hematuria, bladder wall irritation, and painful/frequent micturition.
Methenamine is contraindicated in patients with severe liver disease due to the risk of systemic acidosis.
Hepatic side effects have rarely included transient elevations of AST (SGOT) and ALT (SGPT).
Hypersensitivity reactions have included rashes in 1% to 4% of patients.
Respiratory system side effects may occur in patients with a poor gag reflex or a swallow disorder. Methenamine oral suspension has a vegetable base, and should be used with caution in elderly patients and in those with swallow disorders to prevent lipid pneumonia. Long-term therapy with methenamine suspension has been associated with lipoid pneumonitis in elderly patients.
Ocular side effects have included rare cases of anterior uveitis.
Renal side effects have been more likely and more severe in patients with mild to moderate renal insufficiency. Methenamine is contraindicated in patients with severe renal insufficiency.
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