Methenamine Hippurate Mercury Pharmaceuticals Ltd (Methenamine Hippurate)

Methenamine hippurate is used in the urinary tract infection (UTI) prophylaxis pathway to reduce bacterial colonisation.

• Recurrent urinary tract infections: lowers the frequency of infection episodes in patients with a history of UTIs.
• Uncomplicated urinary tract infections: serves as an adjunctive agent to support bacterial clearance alongside standard therapy.
• Structural urinary abnormalities: provides prophylactic protection in individuals with anatomical factors predisposing to infection.

• After oral administration, methenamine hippurate is excreted unchanged in the urine where, under acidic conditions (pH < 6), it hydrolyses to release formaldehyde and ammonia. Formaldehyde acts as a broad‑spectrum bactericidal agent, denaturing microbial proteins and nucleic acids, thereby inhibiting growth of common urinary pathogens. The resulting antiseptic environment reduces bacterial colonisation of the urinary tract.

Methenamine hippurate may be associated with several adverse reactions, ranging from mild to severe.

Common Side Effects

• Nausea
• Vomiting
• Dyspepsia
• Metallic taste in the mouth
• Headache
• Urinary irritation or burning

Serious or Rare Side Effects

• Allergic skin reactions such as rash or urticaria
• Anaphylaxis
• Hematuria
• Acute renal impairment
• Severe hepatic dysfunction
• Stevens‑Johnson syndrome or toxic epidermal necrolysis

When prescribing methenamine hippurate, clinicians should observe the following precautions.

• Renal function assessment: ensure adequate glomerular filtration before initiating therapy.
• Urine acidity requirement: maintain urinary pH below 6 for optimal drug activation.
• Monitor for hypersensitivity: discontinue if allergic reactions develop.
• Avoid in severe renal impairment: contraindicated when creatinine clearance is markedly reduced.
• Pregnancy and lactation: use only if potential benefit outweighs risk, as safety data are limited.
• Store at ambient temperature: keep below 25 °C in the original packaging, protected from moisture.

Methenamine hippurate can interact with other medicines that alter urine pH or renal handling.

Major Interactions (Avoid)

• Alkalinizing agents (e.g., sodium bicarbonate, potassium citrate): raise urine pH and reduce drug activation.
• Urine‑alkalinizing antibiotics (e.g., nitrofurantoin): diminish antibacterial effect.
• High‑dose vitamin C supplementation: may increase urinary alkalinity.

Moderate Interactions (Monitor Closely)

• Antacids containing magnesium or aluminum: may affect absorption.
• Loop diuretics: alter urinary concentration and excretion.
• Other urinary antiseptics (e.g., methenamine mandelate): additive toxicity risk.
• Renally cleared drugs (e.g., aminoglycosides): monitor renal function.