HEXAMINE

What it is

HEXAMINE contains methenamine hippurate, a salt of methenamine and hippuric acid, which is absorbed and excreted rapidly. Methenamine hippurate is a urinary antibacterial agent with a wide spectrum covering both gram-positive and gram-negative organisms. Each tablet contains 1 g of methenamine hippurate.

Approved indications

— Prophylaxis or suppression of bacteriuria associated with chronic or recurrent infection of the urinary tract.

Dosing overview

For adults and children 12 years or older: 1 tablet twice daily, with or without food. HEXAMINE is not recommended for use in children under 12 years. No dose adjustments are required for patients with mild or moderate renal insufficiency.

Key safety warnings

The effectiveness of methenamine hippurate as a prophylactic agent depends on the acidity of urine, the bacterial species and counts in urine, their susceptibility to methenamine, and the exposure interval to formaldehyde that is hydrolysed from methenamine. Methenamine may be ineffective when the urinary tract is colonised by new species, when bacteria multiply quickly under certain conditions, or when bacteria migrate from the lower urinary tract to the kidneys; therefore patients should be encouraged to consult their doctor at the onset of signs and symptoms of infection. Some sulphonamides may form an insoluble crystalline precipitate with formaldehyde in urine; therefore concurrent administration with methenamine should be avoided. Methenamine hydrolyses into the therapeutically active formaldehyde under acidic conditions in urine; therefore concomitant use with agents that make urine alkaline or urinary alkalising agents such as potassium citrate or acetazolamide reduce the effectiveness of methenamine and should be avoided. In laboratory tests using acid hydrolysis of urine during pregnancy, the presence of methenamine or formaldehyde can result in unmeasurably low oestriol results; enzymatic hydrolysis will provide more accurate results. Methenamine can affect the determination of steroids, catecholamines and 5-hydroxyindole acetic acid in urine and give false results depending on the analytical method used.

Contraindications

Hypersensitivity or allergy to methenamine hippurate, formaldehyde or to any of the excipients. Severe renal failure (eGFR < 10 mL/min/1.73m²), kidney infection, severe dehydration, or gout. Severe hepatic impairment. Metabolic acidosis.

Regulatory history

HEXAMINE methenamine hippurate 1 g tablets were first listed on the ARTG on 3 December 2021.