Hiprex (Methenamine Hippurate)

Hiprex is indicated for the prevention of recurrent urinary tract infections in patients who have a history of such infections.

• Prophylaxis of uncomplicated urinary tract infections in women.
• Prophylaxis of uncomplicated urinary tract infections in men.
• Adjunct to non‑antibiotic measures for patients with recurrent cystitis.
• Long‑term maintenance therapy to reduce infection frequency.
• Use in patients with sterile, acidic urine to enhance drug activation.
• Prophylaxis in patients with neurogenic bladder.
• Prevention of urinary infections associated with catheter use.

• Methenamine hippurate is a pro‑drug that is excreted unchanged in the urine. In an acidic urinary environment (pH < 6), it hydrolyzes to release formaldehyde, a broad‑spectrum antimicrobial agent. Formaldehyde denatures bacterial proteins and nucleic acids, inhibiting bacterial growth and facilitating eradication of susceptible organisms. The conversion is dependent on urinary acidity, making the drug most effective when the urine remains sufficiently acidic.

Adverse reactions to Hiprex are generally uncommon, but they can be categorized by frequency and severity.

Common

• Nausea or an upset stomach, often mild and transient.
• Mild headache that does not require medical intervention.
• Transient dysuria, described as a temporary burning sensation during urination.
• Metallic taste in the mouth, usually resolving after continued use.
• Dry mouth sensation, which is usually mild.
• Mild dizziness.

Serious

• Allergic reactions such as rash, itching, swelling of the face, lips, or tongue.
• Severe skin reactions, including Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Acute renal impairment, particularly in patients with existing kidney disease or dehydration.
• Severe gastrointestinal bleeding, though rare.

When prescribing Hiprex, clinicians should consider several precautionary factors to ensure safe and effective use.

• Assess urinary pH; the drug requires acidic urine (pH < 6) for optimal activation.
• Evaluate renal function before initiation, as impaired kidneys may reduce drug excretion.
• Avoid use in patients with known hypersensitivity to methenamine or hippurate salts.
• Monitor for signs of dehydration, which can concentrate urine and affect drug conversion.
• Use caution in patients with liver disease, although hepatic metabolism is minimal.
• Pregnancy and lactation status should be reviewed, as safety data are limited.
• Consider potential interactions with urinary alkalinizing agents that may raise urine pH.

Hiprex may interact with other medicines or substances that alter urinary pH or renal handling of the drug.

Avoid

• Alkalinizing agents such as sodium bicarbonate, potassium citrate, or acetazolamide.
• Strong urinary acidifiers that may cause excessive acidity and irritation.
• Concurrent use of nephrotoxic drugs in patients with compromised renal function.
• Urinary alkalizing supplements such as potassium bicarbonate.

Use with caution

• Diuretics, which can affect urine concentration and pH.
• Antibiotics that are also excreted in urine, potentially altering urinary flora.
• Drugs that may cause hypersensitivity reactions, such as sulfonamides.
• Medications that affect liver enzymes, although hepatic metabolism of Hiprex is minimal.