Methenamine hippurate
HIPREX
What it isConverted to formaldehyde in acidic urine; recurrent urinary tract infection prophylaxis.
Why this oneIts formaldehyde mechanism largely avoids conventional antibiotic resistance and microbiome pressure.
What limits itUrine must remain below pH 6, and it cannot treat active infection; avoid sulfonamides and urine-alkalinizing drugs.
FDA-approved for
- urinary tract infection prophylaxis
FDA label
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| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Recurrent UTI — prophylaxis/suppression | Adults and children >12 yr | 1 g (1 tablet) BID (morning and night) | 1 g BID | 1 g BID |
| Recurrent UTI — prophylaxis/suppression | Children 6–12 yr | 0.5–1 g (½–1 tablet) BID (morning and night) | 0.5–1 g BID | 1 g BID |
Renal Contraindicated in renal insufficiency.
Hepatic Contraindicated in severe hepatic insufficiency.
Instructions
- Antibacterial activity requires acid urine — restrict alkalinizing foods and medications.
- Supplement urinary acidification if indicated by urinary pH and clinical response.
- Monitor efficacy with repeated urine cultures.
Contraindications
- Renal insufficiency
- Severe hepatic insufficiency
- Severe dehydration
- Concurrent sulfonamides — may form an insoluble precipitate with urinary formaldehyde
Cautions
- Requires acidic urine for activity; alkalinizing foods/drugs blunt efficacy.
Adverse reactions
- Minor reactions in <3.5% of patients: nausea, upset stomach, dysuria, rash
Pregnancy Undefined
Lactation Undefined
NO BOXED WARNINGS
Principal riskIt needs urine pH below 6; prophylaxis only
Cost, est. cash$5–$150/month
Generic entry2003
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.
Mechanism of action: Methenamine hippurate ballicule
