Drug reference

Methenamine

Antibacterial · Urinary Tract Infection Treatment and Prophylaxis

Also known as Hexamine hippurate, Methenamine hippurate

AntibacterialUrinary Tract Infection Treatment and Prophylaxis

CDSCO approved

EXCRETION

—

not curated

INTERACTIONS

7 major

incl. contraindicated

PREGNANCY

Inadequate evidence of safety; widely used for many years without apparent ill consequence, but manufacturer advises preferable to avoid.

FDA category + note

Top interactionssee all 7 →

Sodium BicarbonateContraindicatedDatabaseDDInter
SulfadiazineSevereDatabaseDDInter
SulfadoxineSevereDatabaseDDInter
SulfamethizoleSevereDatabaseDDInter

Mechanism

Methenamine requires an acidic urine for its antimicrobial activity. It is ineffective for upper urinary-tract infections.

Indications

Prophylaxis and long-term treatment of chronic or recurrent uncomplicated lower urinary-tract infectionsProphylaxis and long-term treatment of chronic or recurrent uncomplicated lower urinary-tract infections in patients with catheterschronic, resistant type of urinary tract infections (not involving kidney substance)

Dosing

Adult: For prophylaxis and long-term treatment of chronic or recurrent uncomplicated lower urinary-tract infections: 1 g by mouth every 12 hours. For prophylaxis and long-term treatment of chronic or recurrent uncomplicated lower urinary-tract infections in patients with catheters: 1 g by mouth every 8–12 hours.
Renal adjustment: Avoid if eGFR less than 10 mL/minute/1.73 m2 due to risk of hippurate crystalluria.
Hepatic adjustment: Manufacturer advises avoid.

Contraindications

Gout
Metabolic acidosis
Severe dehydration
acute urinary tract infections
catheterization prophylaxis
renal impairment (effective concentrations may not be reached in urine)

Side effects

Common

Epigastric discomfortSkin reactionsgastritis

Serious

Hippurate crystalluria (risk with eGFR <10 mL/minute/1.73 m2)
chemical cystitis (with high doses for long periods)
haematuria (with high doses for long periods)
CNS symptoms (occasionally)

Pregnancy & lactation

Pregnancy

Inadequate evidence of safety; widely used for many years without apparent ill consequence, but manufacturer advises preferable to avoid.

Lactation

Amount too small to be harmful.

Drug interactions

Sodium Bicarbonate

Contraindicated

Database

Complete loss of therapeutic efficacy of methenamine, rendering it ineffective for treating urinary tract infections.

Concurrent use is contraindicated. If methenamine is prescribed, avoid all alkalinizing agents, including sodium bicarbonate. Choose an alternative antimicrobial or an alternative urinary acidifier if needed.

Source: DDInter

Sulfadiazine

Severe

Database

Clinical effect not specified

Source: DDInter

Sulfadoxine

Severe

Database

Clinical effect not specified

Source: DDInter

Sulfamethizole