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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
  • 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


This drug was generally well tolerated. Minor side effects have been reported in less than 3.5% of patients and were reversible when the drug was stopped.[Ref]


Uncommon (0.1% to 1%): Rash, pruritus
Frequency not reported: Generalized skin rash[Ref]


Uncommon (0.1% to 1%): Gastric irritation
Frequency not reported: Nausea, vomiting, upset stomach, stomatitis, gastrointestinal disturbances, diarrhea, abdominal cramping[Ref]


High doses have been associated with albuminuria, gross hematuria, bladder irritation, and painful/frequent micturition.[Ref]

Uncommon (0.1% to 1%): Bladder irritation
Frequency not reported: Dysuria, hematuria, urinary frequency, albuminuria[Ref]


Frequency not reported: Elevated AST, elevated ALT[Ref]


Frequency not reported: Hypersensitivity reactions[Ref]


Frequency not reported: Anorexia


Frequency not reported: Anterior uveitis[Ref]


1. "Product Information. Hiprex (methenamine)." Hoechst Marion-Roussel Inc, Kansas City, MO.

2. Cerner Multum, Inc. "Australian Product Information." O 0

3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

4. Gleckman R, Alvarez S, Joubert D, Matthews S "Drug therapy reviews: methenamine mandelate and methenamine hippurate." Am J Hosp Pharm 36 (1979): 1509-12

5. "Product Information. Mandelamine (methenamine)." Parke-Davis, Morris Plains, NJ.

6. Australian Drug Evaluation Committee "Adverse effects of drugs commonly used in the treatment of urinary tract infection." Med J Aust 1 (1972): 435-8

7. Brumfitt W, Hamilton-Miller J, Gargan R, Cooper J, Smith GW "Long-term prophylaxis of urinary infections in women: comparative trial of trimethoprim, methenamine hippurate and topical povidone-iodine." J Urol 130 (1983): 1110-4

8. Brumfitt W, Cooper J, Hamilton-Miller J "Prevention of recurrent urinary infections in women: a comparative trial between nitrofurantoin and methenamine hippurate." J Urol 126 (1981): 71-4

9. Kolker RJ "Medication-induced bilateral anterior uveitis." Arch Ophthalmol 109 (1991): 1343

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