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Methenamine

    Brands

    DEA Class; Rx

    Common Brand Names; Hiprex, Urex

    • Antibiotics, Other

    Urinary antiinfective
    Used for suppression and prophylaxis of frequently recurring urinary tract infections
    Contraindicated in patients with renal insufficiency, severe hepatic insufficiency, and severe dehydration

    Indicated for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary

    Hypersensitivity to methenamine or tartrazine (FD&C Yellow No. 5)

    Severe renal or hepatic insufficiency

    Concurrent sulfonamides or acetazolamide may form insoluble precipitate in urine

    Dysuria

    Gastric upset

    Nausea

    Rash

    Patients with pre-existing hepatic insufficiency may suffer adverse effects from the small amounts of ammonia and formaldehyde that are produced; the classical syndrome of acute hepatic failure may be evoked in these patients

    Taking therapy in absence of proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to patient and increases risk of development of drug-resistant bacteria

    Large doses of methenamine (8 g daily for 3 to 4 weeks) have caused bladder irritation, painful and frequent micturition, albuminuria, and gross hematuria

    Maintain acidic pH of urine, especially when treating urea-splitting organisms, e.g. Proteus, Pseudomonas

    Monitor LFTs, especially in patients with history of liver impairment

    Safe use not established during pregnancy, especially 1st and 2nd trimester

    May precipitate uric acid stones in patients with gout

    Pregnancy Category: C

    Lactation: excreted in breast milk; no adverse effects documented

    Adults

    4 g/day PO methenamine mandelate; 2 g/day PO methenamine hippurate.

    Geriatric

    4 g/day PO methenamine mandelate; 2 g/day PO methenamine hippurate.

    Adolescents

    4 g/day PO methenamine mandelate; 2 g/day PO methenamine hippurate.

    Children

    6 to 12 years: 2 g/day PO methenamine mandelate; 2 g/day PO methenamine hippurate.
    Younger than 6 years: 73.6 mg/kg/day PO methenamine mandelate; safety and efficacy of methenamine hippurate have not been established.

    Infants

    Safety and efficacy have not been established.

    Neonates

    Safety and efficacy have not been established.

    Methenamine hippurate

    oral solution

    • 500mg/5mL

    tablet, hippurate

    • 1g

    tablet, mandelate

    • 500mg
    • 1g