Hiprex (Methenamine Hippurate)

Hiprex is indicated for the prevention of recurrent urinary tract infections in patients who have experienced multiple episodes.

• Long‑term prophylaxis in adults with a history of uncomplicated cystitis.
• Adjunct to behavioral measures such as increased fluid intake and bladder emptying.
• Use in patients with normal to acidic urine pH where methenamine can be hydrolysed.
• Consideration for individuals who cannot tolerate chronic antibiotic therapy.
• May be prescribed after an acute infection has been successfully treated to reduce recurrence.

• Methenamine hippurate is a pro‑drug that is excreted unchanged in the urine. In an acidic urinary environment (pH ≤ 6), it undergoes non‑enzymatic hydrolysis to release formaldehyde and ammonia. The generated formaldehyde acts as a broad‑spectrum bactericidal agent, denaturing bacterial proteins and nucleic acids, thereby inhibiting the growth of susceptible uropathogens within the bladder and urethra. Because activity depends on urine acidity, patients are advised to keep urinary pH low, and the drug does not have systemic antibacterial effects.

Adverse reactions to Hiprex are generally mild, but rare serious events have been reported.

Common

• Nausea or upset stomach, often mild and transient.
• Dyspepsia or heartburn that may improve with food.
• Mild skin rash or itching without swelling.
• Transient headache that resolves without medication.
• Metallic taste in the mouth during treatment.
• Increased urinary frequency, usually temporary.

Serious

• Severe allergic reaction such as anaphylaxis, requiring immediate medical attention.
• Acute interstitial nephritis presenting with flank pain and impaired kidney function.
• Persistent or worsening urinary symptoms despite therapy, indicating possible infection progression.
• Seizures (rare) that may occur in susceptible individuals.
• Hepatic dysfunction manifested by elevated liver enzymes.
• Blood dyscrasias (e.g., agranulocytosis) leading to low white blood cell counts.

• When prescribing Hiprex, clinicians