Methenamine Side Effects

It is possible that some side effects of methenamine may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to methenamine: oral suspension, oral tablet, oral tablet enteric coated

Along with its needed effects, methenamine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking methenamine:

Less common
  • Skin rash
Rare
  • Blood in urine
  • lower back pain
  • pain or burning while urinating

Some side effects of methenamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common
  • Nausea and vomiting

For Healthcare Professionals

Applies to methenamine: compounding powder, oral suspension, oral tablet

General

Methenamine is generally well tolerated. Minor side effects have been reported in less than 3.5% of patients.

Dermatologic

Dermatologic side effects have included rash and pruritus.

Gastrointestinal

Gastrointestinal side effects have included nausea, vomiting, diarrhea, anorexia, and abdominal cramping.

Genitourinary

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.

Hepatic

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

Hypersensitivity reactions have included rashes in 1% to 4% of patients.

Respiratory

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

Ocular side effects have included rare cases of anterior uveitis.

Renal

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.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. Drugs.com does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.

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