Methenamine
Methenamine is an antibacterial medication used primarily to prevent and treat recurrent urinary tract infections. It works as a urinary antiseptic by converting to formaldehyde in acidic urine, which inhibits bacterial growth.
Methenamine is a urinary antiseptic used for preventing recurrent bladder infections by releasing antibacterial formaldehyde in acidic urine.
Key facts at a glance
- ATC
- J01XX05
- RxNorm
- 6851
- Generic
- Methenamine
- Class
- atc-j01
- Brands
- Hyophen, Phosphasal, Ustell, Prosed DS, Urogesic Blue Reformulated Apr 2012, Urimar Reformulated Oct 2013, Hiprex, Urin DS, Uro-Blue, Azo Urinary Tract Defense, Cystex, Uretron DS, Urex, Uroqid-Acid No.2, Uribel Tabs
- Availability
- otc
- Pregnancy
- C
- Lactation
- caution
- Half-life (h)
- 4
- Onset (min)
- 0
- Duration (h)
- 12
- Routes
- oral
- Forms
- tablet
- Regions
- United States, Canada, United Kingdom, Australia, Germany, France, Europe
- Monitoring
- urine pH, serum creatinine, liver enzymes, complete blood count
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 500mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 250mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 400mg daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
9 groupspregnancy
first trimesteravoid if possible
avoid use during pregnancy unless benefits outweigh risks
regular fetal monitoring
Use of this medication in this population requires careful consideration of risks and benefits.
pregnancy
second trimesteruse lowest effective dose
use only if clearly needed and benefits outweigh potential risks
periodic fetal monitoring
Use with caution and monitor for adverse effects.
pregnancy
third trimesteruse lowest effective dose
use only if clearly needed; avoid close to delivery due to potential formaldehyde exposure
monitor fetal well-being
Use with caution and monitor for adverse effects.
lactation
breastfeedingdiscontinue breastfeeding or avoid drug
methenamine passes into breast milk; avoid breastfeeding during treatment
not applicable
Use of this medication in this population requires careful consideration of risks and benefits.
geriatric
elderlyreduce dose based on renal function
use with caution; assess renal function before initiating therapy; start at lowest effective dose
monitor renal function and for adverse effects
Use with caution and monitor for adverse effects.
pediatric_age
children under 12not recommended
not recommended for children under 12 years of age; safety and effectiveness not established
not applicable
Use of this medication in this population requires careful consideration of risks and benefits.
renal_impairment
mild moderateadjust dose and dosing interval
use with caution; may need reduced dose; ensure adequate hydration and acidic urine
monitor renal function periodically
Use with caution and monitor for adverse effects.
renal_impairment
severeavoid use
contraindicated in patients with severe renal impairment or renal insufficiency
not applicable
Use of this medication in this population requires careful consideration of risks and benefits.
hepatic_impairment
moderate severeuse with caution
use with caution in hepatic impairment; monitor liver function
monitor liver function tests
Use with caution and monitor for adverse effects.
Statistics and clinical data
FDA approval year
Original FDA approval for methenamine hippurate and methenamine mandelate
Drug class
ATC code J01XX01 - methenamine
Common uses
Prevention of recurrent urinary tract infections
Mechanism of action
Antibacterial action via formaldehyde release
Prevention and treatment of recurrent urinary tract infections, particularly uncomplicated cystitis in patients with recurrent infections. Sometimes used for urinary tract antisepsis following urological procedures.
Methenamine is a prodrug that hydrolyzes to formaldehyde in acidic urine (pH below 6). The released formaldehyde denatures proteins and nucleic acids of bacteria, providing a nonspecific antibacterial effect in the urinary tract.
Requires acidic urine (pH < 6) for effectiveness; urine acidification may be necessary. Not suitable for renal parenchymal infections. Avoid in patients with severe hepatic or renal impairment. May cause gastrointestinal upset and urinary irritation. Hipproate and mandelate salts are the common oral formulations.
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 26, 2026. · Read our editorial policy