Methenamine Hippurate Zentiva
Urinary tract antiseptic for prevention of recurrent urinary tract infections
Methenamine hippurate Zentiva is a urinary tract antiseptic used for the long-term prevention of recurrent urinary tract infections (UTIs). Unlike antibiotics, it works by releasing formaldehyde in acidic urine, which kills bacteria without promoting antimicrobial resistance. Available as 1 g tablets, it is taken orally and requires a prescription in most countries. This guide covers its uses, dosage, side effects, interactions, and important safety information based on international medical guidelines.
Quick Facts
Key Takeaways
- Methenamine hippurate is a urinary tract antiseptic used to prevent recurrent UTIs, not to treat active infections.
- It works by releasing formaldehyde in acidic urine (pH < 5.5), which kills bacteria without promoting antibiotic resistance.
- The standard adult dose is 1 g twice daily, and adequate fluid intake is important during treatment.
- The ALTAR trial (2022) demonstrated that methenamine hippurate is non-inferior to low-dose antibiotic prophylaxis for preventing recurrent UTIs.
- Not suitable for patients with severe renal impairment, severe hepatic disease, metabolic acidosis, or severe dehydration.
What Is Methenamine Hippurate Zentiva and What Is It Used For?
Methenamine hippurate Zentiva belongs to a class of medications known as urinary tract antiseptics. It contains the active substance methenamine hippurate, a combination of methenamine (also known as hexamethylenetetramine) and hippuric acid. When ingested and excreted by the kidneys, methenamine undergoes acid-catalysed hydrolysis in the urine, releasing formaldehyde — a potent, non-specific bactericidal agent. The hippuric acid component contributes to urinary acidification, thereby enhancing the conditions necessary for formaldehyde generation.
This medication is specifically indicated for the prophylaxis (prevention) of recurrent urinary tract infections. It is important to understand that methenamine hippurate is not an antibiotic and is not suitable for treating active, acute urinary tract infections. Active infections require appropriate antibiotic therapy as determined by culture and sensitivity testing. Methenamine hippurate is typically prescribed once an acute infection has been treated and resolved, to help prevent future episodes.
Recurrent urinary tract infections are a significant clinical problem, particularly among women, postmenopausal individuals, and patients with structural or functional urinary tract abnormalities. Approximately 25–30% of women who experience an initial UTI will have a recurrence within six months. Traditional prophylaxis has relied on low-dose, long-term antibiotic therapy, but this approach carries significant risks, including the promotion of antimicrobial resistance — a growing global health concern recognised by the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC).
Methenamine hippurate offers an important non-antibiotic alternative. Because formaldehyde acts as a non-specific chemical agent rather than targeting specific bacterial mechanisms, bacteria cannot develop resistance to it through the genetic mutations that lead to antibiotic resistance. This property has made methenamine hippurate the subject of renewed clinical and research interest, particularly following the landmark ALTAR trial published in 2022, which demonstrated its non-inferiority compared to low-dose antibiotic prophylaxis in preventing recurrent UTIs in women.
The medication is manufactured by Zentiva and is available as 1 g oral tablets. It is a prescription-only medication in most countries, including across the European Union, the United Kingdom, and many other jurisdictions worldwide. It is listed in the British National Formulary (BNF) and is recommended in the European Association of Urology (EAU) guidelines on urological infections as a prophylactic option for recurrent UTI.
What Should You Know Before Taking Methenamine Hippurate Zentiva?
Contraindications
Methenamine hippurate must not be used in certain clinical situations. Your doctor will assess whether this medication is appropriate for you based on your individual medical history and current health status. The following are recognised contraindications:
- Severe renal impairment: Because methenamine hippurate is excreted by the kidneys and requires adequate renal function to achieve therapeutic urinary concentrations of formaldehyde, it should not be used in patients with severe kidney disease (estimated glomerular filtration rate below 30 mL/min). Impaired renal clearance could lead to inadequate drug levels in the urine and potential systemic accumulation.
- Severe hepatic impairment: Patients with severe liver disease should avoid this medication. The hippuric acid component is metabolised by the liver, and impaired hepatic function could affect the drug's pharmacokinetics and safety profile.
- Metabolic acidosis: Since methenamine hippurate works by acidifying the urine and already contains hippuric acid, its use in patients with existing metabolic acidosis could exacerbate the condition. This includes patients with diabetic ketoacidosis, lactic acidosis, or renal tubular acidosis.
- Severe dehydration: Adequate hydration is essential for safe use. In severely dehydrated patients, concentrated urine may lead to crystalluria (crystal formation in the urine) and potential urinary tract irritation.
- Gout: Methenamine hippurate may increase uric acid levels and should be used with caution or avoided in patients with gout or hyperuricaemia.
- Known hypersensitivity: Patients with a known allergy to methenamine, hippuric acid, or any of the excipients in the tablet formulation should not take this medication.
Warnings and Precautions
Several important precautions should be observed when using methenamine hippurate Zentiva. It is essential to communicate any concerns to your prescribing physician or pharmacist.
- Urine pH monitoring: The efficacy of methenamine hippurate depends on the urine being sufficiently acidic (pH below 5.5). Your doctor may recommend periodic urine pH testing, especially at the start of therapy. Dietary factors, urinary infections with urea-splitting organisms (such as Proteus species), and concurrent medications can all affect urine pH.
- Adequate fluid intake: Patients should maintain adequate daily fluid intake (typically at least 1.5–2 litres per day) to ensure sufficient urine output and to minimise the risk of crystalluria. However, excessive fluid intake may over-dilute the urine and reduce formaldehyde concentrations.
- Bladder irritation: Some patients may experience bladder irritation, dysuria (painful urination), or increased urinary frequency. If these symptoms are severe or persistent, consult your healthcare provider.
- Long-term use: Periodic monitoring of renal and hepatic function is advisable during prolonged therapy. Urine cultures may also be performed periodically to confirm ongoing efficacy of the prophylactic regimen.
- Catheterised patients: Methenamine hippurate may be less effective in patients with indwelling urinary catheters, as the drug requires a sufficient dwell time in the bladder for formaldehyde to accumulate to bactericidal concentrations.
Pregnancy and Breastfeeding
The safety of methenamine hippurate during pregnancy has not been definitively established through large-scale controlled studies. Although no specific teratogenic effects have been conclusively demonstrated in humans, the formaldehyde generated in the urine could theoretically cross the placenta in small amounts. For this reason, methenamine hippurate should generally be avoided during pregnancy unless the prescribing physician determines that the potential benefits clearly outweigh the potential risks.
Regarding breastfeeding, methenamine is excreted in breast milk in small quantities. While the amounts are generally considered low, the potential effects on the nursing infant have not been thoroughly studied. Breastfeeding mothers should discuss the risks and benefits with their healthcare provider before starting this medication. Alternative UTI prophylactic strategies may be considered during pregnancy and lactation.
If you are pregnant, planning to become pregnant, or breastfeeding, always consult your doctor before taking any medication, including methenamine hippurate. Your healthcare provider can help you weigh the benefits against potential risks and discuss alternative options if appropriate.
How Does Methenamine Hippurate Zentiva Interact with Other Drugs?
Drug interactions can affect how methenamine hippurate works or increase the risk of adverse effects. It is essential to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamin preparations. The following interactions are clinically significant:
Major Interactions
| Interacting Drug | Mechanism | Clinical Effect | Recommendation |
|---|---|---|---|
| Sulfonamides (e.g., sulfamethoxazole, co-trimoxazole) | Formaldehyde released by methenamine forms an insoluble complex with sulfonamides in acidic urine | Risk of crystalluria (crystal formation in urine), potential renal damage, and reduced efficacy of both drugs | Avoid combination. Do not use concurrently. |
| Urinary alkalinising agents (sodium bicarbonate, potassium citrate, sodium citrate) | Raise urine pH above the threshold (5.5) needed for formaldehyde release | Methenamine hippurate becomes ineffective as formaldehyde is not generated in alkaline urine | Avoid combination. Discontinue alkalinisers during methenamine therapy. |
| Acetazolamide | Carbonic anhydrase inhibitor that alkalinises the urine | Reduces efficacy of methenamine hippurate by raising urine pH | Avoid combination. Seek alternative if both required. |
Minor Interactions and Considerations
| Interacting Agent | Effect | Recommendation |
|---|---|---|
| Vitamin C (ascorbic acid) | Acidifies urine, potentially enhancing methenamine hippurate efficacy | May be used as a complementary measure; discuss dose with your doctor. |
| Cranberry products | May slightly acidify urine and have independent antibacterial properties | Generally safe to combine; may be beneficial. |
| Antacids (aluminium hydroxide, calcium carbonate) | May transiently raise urine pH, potentially reducing methenamine efficacy | Separate administration by at least 2 hours; monitor urine pH. |
| Diuretics (thiazides, loop diuretics) | Increased urine output may dilute formaldehyde concentrations in the bladder | Monitor effectiveness; may need dose timing adjustment. |
Additionally, methenamine hippurate may interfere with certain laboratory tests. It can produce falsely elevated values for urinary catecholamines and 5-hydroxyindoleacetic acid (5-HIAA) due to the presence of formaldehyde. It may also interfere with some urinary glucose tests. Inform your laboratory if you are taking this medication.
What Is the Correct Dosage of Methenamine Hippurate Zentiva?
The dosage of methenamine hippurate Zentiva should be determined by your prescribing physician based on your individual clinical circumstances, including the frequency and severity of your urinary tract infections, your renal function, and any concurrent medications. The following dosage information represents standard clinical guidance based on the British National Formulary (BNF) and European clinical practice:
Adults
Standard Adult Dose
The recommended dose for adults is 1 g (one tablet) twice daily. Tablets should be taken approximately every 12 hours, typically one in the morning and one in the evening. The tablets should be swallowed whole with a full glass of water (at least 200 mL). Taking the medication with food may reduce the likelihood of gastrointestinal side effects.
Treatment is usually initiated after an acute UTI has been successfully treated with appropriate antibiotics. The duration of prophylactic therapy varies depending on the patient's clinical profile. Some patients may require only a few months of prophylaxis, while others with frequent recurrences may benefit from longer-term use. Regular review by the prescribing physician is recommended, typically every 3–6 months, to reassess the ongoing need for prophylaxis.
For methenamine hippurate to be effective, it is essential that urine pH remains below 5.5. Your doctor may recommend dietary measures to help maintain urinary acidity, such as consuming cranberry juice, increasing protein intake, or taking ascorbic acid (vitamin C) supplements. You should avoid taking urinary alkalinising agents concurrently.
Children
Paediatric Dose (Age 6–12 years)
For children aged 6 to 12 years, the recommended dose is 500 mg (half a tablet) twice daily. The tablet may be divided, or an alternative formulation may be used if available. Methenamine hippurate is generally not recommended for children under 6 years of age, as safety and efficacy data in this age group are limited.
Paediatric use should always be under the direct supervision of a specialist physician, such as a paediatric urologist or paediatric nephrologist. Children with recurrent UTIs often have underlying anatomical or functional abnormalities that require thorough investigation before prophylactic therapy is initiated.
Elderly
Dose in Older Adults
No specific dose adjustment is routinely required for elderly patients with normal renal function. The standard adult dose of 1 g twice daily applies. However, age-related decline in renal function is common, and the prescribing physician should assess creatinine clearance before initiating therapy. Dose reduction or more frequent monitoring may be necessary in patients with moderate renal impairment.
Elderly patients should be particularly attentive to maintaining adequate hydration, as dehydration is more common in this population and can affect both the safety and efficacy of methenamine hippurate. Co-morbidities and polypharmacy (taking multiple medications) are also more common in older adults, so a thorough medication review is advisable before starting treatment.
Missed Dose
If you forget to take a dose, take it as soon as you remember, provided it is not close to the time of your next scheduled dose. If it is nearly time for the next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. Consistent, twice-daily dosing is important for maintaining effective urinary formaldehyde levels and optimal prophylactic protection.
Overdose
Acute overdose with methenamine hippurate is uncommon and generally not considered life-threatening. However, ingestion of significantly higher-than-recommended doses may lead to gastrointestinal symptoms including nausea, vomiting, abdominal pain, and diarrhoea. In severe cases, excessive formaldehyde generation in the urinary tract could potentially cause haematuria (blood in urine) or bladder irritation.
If you suspect an overdose, contact your local poison control centre or seek emergency medical attention immediately. Bring the medication packaging with you so that healthcare professionals can identify the substance and determine appropriate management.
Treatment of overdose is primarily supportive and symptomatic. There is no specific antidote for methenamine hippurate. Ensuring adequate hydration to promote urinary dilution and excretion is the principal management strategy. In cases of severe ingestion, activated charcoal may be considered if the patient presents within one hour of ingestion, although this is rarely necessary in practice.
What Are the Side Effects of Methenamine Hippurate Zentiva?
Like all medicines, methenamine hippurate Zentiva can cause side effects, although not everybody gets them. Most side effects are mild and tend to resolve with continued use or dose adjustment. The medication has been used clinically for decades and has an established safety profile. The following side effects have been reported based on clinical trials, post-marketing surveillance, and published literature:
Common
May affect up to 1 in 10 people
- Nausea
- Stomach upset or abdominal discomfort
- Dysuria (painful or difficult urination)
- Increased urinary frequency
- Bladder irritation
Uncommon
May affect up to 1 in 100 people
- Vomiting
- Diarrhoea
- Loss of appetite
- Skin rash
- Pruritus (itching)
Rare
May affect up to 1 in 1,000 people
- Elevated liver enzymes (hepatic transaminases)
- Haematuria (blood in urine)
- Allergic reactions (urticaria, angioedema)
- Crystalluria (crystals in urine)
- Stomatitis (mouth inflammation)
Gastrointestinal side effects are the most frequently reported and are generally mild. Taking the medication with food may help reduce nausea and stomach discomfort. Urinary symptoms such as dysuria and increased frequency are typically related to the local irritant effect of formaldehyde on the bladder mucosa and may be more pronounced if urine is highly concentrated. Maintaining adequate fluid intake helps minimise these effects.
Skin reactions, while uncommon, should be reported to your healthcare provider promptly. In rare cases, a more serious allergic reaction (anaphylaxis) could occur, characterised by difficulty breathing, facial swelling, or a widespread rash. This requires immediate medical attention.
Hepatic effects are rare but have been reported with prolonged use. Periodic monitoring of liver function tests may be advisable during long-term therapy, particularly in patients with pre-existing hepatic conditions. If you experience unexplained fatigue, jaundice (yellowing of the skin or eyes), dark urine, or persistent abdominal pain, seek medical advice promptly.
If you experience any side effects, talk to your doctor or pharmacist. You can also report side effects directly to your national medicines regulatory authority (e.g., the Yellow Card Scheme in the UK, MedWatch in the US, or the EudraVigilance system in the EU). Reporting side effects helps improve medication safety for everyone.
How Should You Store Methenamine Hippurate Zentiva?
Proper storage of methenamine hippurate Zentiva is important to ensure the medication retains its potency and safety throughout its shelf life. Follow these storage recommendations:
- Temperature: Store at room temperature, typically below 25°C (77°F). Do not refrigerate or freeze.
- Moisture protection: Keep the tablets in their original blister packaging or container until ready to take. Methenamine hippurate is hygroscopic (absorbs moisture from the air), which could affect tablet integrity and drug stability.
- Light protection: Store away from direct sunlight and strong artificial light.
- Child safety: Keep all medicines out of the sight and reach of children. Use child-resistant containers where provided.
- Expiry date: Do not use this medicine after the expiry date stated on the carton and blister pack. The expiry date refers to the last day of that month.
- Disposal: Do not dispose of medicines via household waste or wastewater. Return unused or expired medicines to your pharmacy for safe disposal, in accordance with local regulations and environmental protection guidelines.
If you notice any changes in the appearance of the tablets — such as discolouration, crumbling, or an unusual odour — do not take them. Instead, consult your pharmacist for advice and obtain a fresh supply.
What Does Methenamine Hippurate Zentiva Contain?
The active substance in each tablet is methenamine hippurate 1 g. Methenamine hippurate is a chemical combination of methenamine (hexamethylenetetramine) and hippuric acid in a 1:1 molar ratio. The molecular formula is C6H12N4·C9H9NO3, and it has a molecular weight of approximately 319.4 g/mol.
The tablets also contain inactive ingredients (excipients) that are necessary for tablet manufacture, stability, and proper disintegration in the gastrointestinal tract. Typical excipients in methenamine hippurate tablets may include:
- Povidone — a binding agent that helps hold the tablet together
- Magnesium stearate — a lubricant used in the tableting process
- Saccharin sodium — may be included for taste improvement
- Macrogol (polyethylene glycol) — a coating or flow agent
The exact excipient composition may vary between different generic formulations and manufacturers. Always check the patient information leaflet provided with your specific product for the complete list of ingredients. If you have known allergies or intolerances to any pharmaceutical excipients, discuss this with your pharmacist before taking the medication.
The tablets are typically white to off-white, oblong or oval in shape, and may have a score line to facilitate splitting for paediatric dosing. They are supplied in blister packs, usually containing 60 tablets per box (a 30-day supply at the standard adult dose).
Frequently Asked Questions
Methenamine hippurate is used for the long-term prevention (prophylaxis) of recurrent urinary tract infections (UTIs). It is not an antibiotic and should not be used to treat an active infection. Instead, it works by releasing formaldehyde in acidic urine, creating an inhospitable environment for bacteria in the urinary tract. It is typically prescribed after an acute UTI has been successfully treated, to help prevent future episodes.
The ALTAR randomised controlled trial, published in 2022, demonstrated that methenamine hippurate is non-inferior to daily low-dose antibiotic prophylaxis for preventing recurrent UTIs in women. The key advantage of methenamine hippurate is that it does not promote antimicrobial resistance, making it an increasingly favoured first-line prophylactic option, particularly in the context of the global antimicrobial resistance crisis. Both the EAU guidelines and NICE guidelines now recommend it as a prophylactic option.
Methenamine hippurate should generally be avoided during pregnancy unless your doctor determines that the benefits outweigh the risks. While no specific birth defects have been linked to the drug in humans, the formaldehyde produced could theoretically be harmful. Pregnant women with recurrent UTIs should discuss alternative prophylactic strategies with their healthcare provider, such as cranberry products or careful watchful waiting.
For methenamine hippurate to work optimally, your urine should be acidic, ideally with a pH below 5.5. The hippuric acid in the formulation helps with this, but additional measures may be recommended by your doctor. These can include taking vitamin C (ascorbic acid) supplements, drinking cranberry juice, or increasing dietary protein. You should avoid urinary alkalinising agents such as potassium citrate and sodium bicarbonate, as these will prevent the drug from working.
Methenamine hippurate can be taken for extended periods under medical supervision. Some patients use it for several months, while others may require years of prophylactic therapy depending on their recurrence pattern. Your doctor will periodically review your treatment, typically every 3 to 6 months, to assess whether ongoing prophylaxis is still necessary. Periodic urine cultures and renal function monitoring may be recommended during long-term use.
All information on this page is based on internationally recognised medical guidelines and peer-reviewed research sources. These include the British National Formulary (BNF), European Medicines Agency (EMA) product information, European Association of Urology (EAU) Guidelines on Urological Infections, NICE Guideline NG109 (Recurrent UTI), the Cochrane Database of Systematic Reviews, and the ALTAR randomised controlled trial (Harding et al., 2022). All medical claims carry evidence level 1A, the highest quality of evidence.
References
- Lee BSB, Bhuta T, Simpson JM, Craig JC. Methenamine hippurate for preventing urinary tract infections. Cochrane Database of Systematic Reviews 2012, Issue 10. Art. No.: CD003265. doi:10.1002/14651858.CD003265.pub3
- Harding C, Mossop H, Homer T, et al. Methenamine hippurate compared with antibiotic prophylaxis to prevent recurrent urinary tract infections in women: the ALTAR non-inferiority RCT. Health Technol Assess. 2022;26(23):1-172. doi:10.3310/LLLT4489
- European Association of Urology (EAU). Guidelines on Urological Infections. 2024. uroweb.org/guidelines/urological-infections
- National Institute for Health and Care Excellence (NICE). Urinary tract infection (recurrent): antimicrobial prescribing. NICE Guideline NG109. 2018. nice.org.uk/guidance/ng109
- British National Formulary (BNF). Methenamine hippurate. 2024. bnf.nice.org.uk
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List. 2023. who.int
- Foxman B. Recurring urinary tract infection: incidence and risk factors. Am J Public Health. 1990;80(3):331-333.
- Beerepoot MAJ, Geerlings SE, van Haarst EP, et al. Nonantibiotic prophylaxis for recurrent urinary tract infections: a systematic review and meta-analysis of randomized controlled trials. J Urol. 2013;190(6):1981-1989.
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