Urex Side Effects

Generic Name: methenamine

Note: This page contains side effects data for the generic drug methenamine. It is possible that some of the dosage forms included below may not apply to the brand name Urex.

It is possible that some side effects of Urex 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

As well as its needed effects, methenamine (the active ingredient contained in Urex) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking methenamine, check with your doctor immediately:

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

Some methenamine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common
  • Nausea and vomiting

For Healthcare Professionals

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

General

Methenamine (the active ingredient contained in Urex) 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 (the active ingredient contained in Urex) 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 (the active ingredient contained in Urex) 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 (the active ingredient contained in Urex) is contraindicated in patients with severe renal insufficiency.

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