Methenamine hippurate

Description

Methenamine hippurate is a broad-spectrum urinary antiseptic agent. Under acidic conditions, methenamine hippurate is hydrolyzed to formaldehyde and ammonia, which exerts an antibacterial effect. It is effective against a wide range of bacteria but lacks activity against Proteus and other bacteria that increase urine alkalinity. Formulations containing methenamine hippurate have been used to treat urinary tract infections.

Chemical properties

White Solid

Originator

Hiprex ,Merrell National,US,1967

The Uses of Methenamine hippurate

Antibacterial (urinary).

Definition

ChEBI: Methenamine hippurate is a N-acylglycine. It is functionally related to a N-benzoylglycine.

Manufacturing Process

179 g (1 mol) hippuric acid (benzoyl glycine) and 140 g (1 mol) hexamethylenetetramine were heated under reflux in 500 ml methanol. The small amount of water necessary to give a clear, homogeneous solution was added to the resulting reaction mixture which was then evaporated to dryness. The residue soon crystallized, a procedure that could be greatly accelerated by seeding with crystals of hexamethylenetetramine hippurate from a previous preparation. The resulting solid product was broken up and pulverized. Hexamethylenetetramine hippurate is stable on exposure to air and is soluble in water and alcohol. It melts at 105° to 110°C.

brand name

Urex(Vatring).

Therapeutic Function

Antibacterial (urinary)

General Description

Methenamine hippurate (Hiprex) is the hippuric acid salt ofmethenamine. It is readily absorbed after oral administrationand is concentrated in the urinary bladder, where it exerts itsantibacterial activity. Its activity is increased in acid urine.

Clinical Use

Antibacterial agent

Drug interactions

Potentially hazardous interactions with other drugs
Antibacterials: increased risk of crystalluria with sulphonamides.
Diuretics: effects antagonised by acetazolamide.

Metabolism

Under acid conditions methenamine is slowly hydrolysed to formaldehyde and ammonia. Almost no hydrolysis of methenamine takes place at physiological pH, and it is therefore virtually inactive in the body. Methenamine is rapidly and almost completely eliminated in the urine, and provided this is acidic (preferably below pH 5.5) bactericidal concentrations of formaldehyde occur. Because of the time taken for hydrolysis, however, these do not occur until the urine reaches the bladder.