Methenamine is an interesting compound with several uses. It's primarily known for its medical applications, particularly as an antibiotic agent. When methenamine is ingested, it's converted in the acidic environment of the urinary tract into formaldehyde and ammonia, which are toxic to bacteria. This property makes it useful in the treatment and prevention of urinary tract infections (UTIs). It's often prescribed prophylactically for individuals prone to recurrent UTIs.

Methenamine (Hiprex) is available as Methenamine Hippurate and Mandelate. It is hydrolyzed in urine to formaldehyde that has bactericidal effects.

Methenamine (Hiprex) Uses:

• Prophylaxis and suppressive treatment of Urinary tract infection:
  • When long-term therapy is necessary following the administration of the proper antimicrobial medication to completely eliminate the infection, it is used as a preventative and suppressive treatment for recurring urinary tract infections.

Methenamine (Hiprex) Dose in Adults:

Methenamine (Hiprex) Dose in the prophylactic and suppressive treatment of Urinary tract infection:

• For the hippurate form: 1,000 milligrams twice a day orally.
• For the mandelate form: 1,000 milligrams four times a day orally.

Taking methenamine as prescribed by your doctor can help fight off UTIs or prevent them from coming back.

Methenamine (Hiprex) Dose in Childrens:

• The Urine should be acidic with a PH preferably less than 5.5 for optimal efficacy.

Methenamine (Hiprex) Dose in the prophylaxis and suppression of Urinary tract infection:

Methenamine hippurate:

• For children aged 6 to 12 years: Take 500 to 1,000 milligrams twice a day by mouth.
• For adolescents: Take 1,000 milligrams twice a day by mouth.

Methenamine mandelate:

• For children under 6 years old: Take 50 to 75 milligrams per kilogram per day, divided into doses every 6 to 8 hours, with a maximum dose of 500 milligrams per dose.
• For children aged 6 to 12 years: Take 500 milligrams four times a day by mouth.
• For adolescents: Take 1,000 milligrams four times a day by mouth.

Pregnancy Risk Factor C (methenamine mandelate)

• When it comes to pregnancy, methenamine hippurate, another form of methenamine, hasn't shown any adverse effects in animal studies, but there haven't been studies on methenamine mandelate.
• Methenamine can pass through the placenta to the amniotic fluid, but studies haven't found an increased risk of harm to the baby.
• However, it's important to note that methenamine might affect urine estriol levels if measured using acid hydrolysis, but using enzyme hydrolysis can prevent this issue.

Use of methenamine during lactation

• Since methenamine can be passed into breast milk, there's a chance it could cause serious reactions in the nursing baby.
• Because of this risk, the manufacturer suggests deciding whether to stop breastfeeding or stop taking the medication, considering how crucial the treatment is for the mother.
• It's important to weigh the benefits of the treatment against the potential risks to the baby when making this decision.

Methenamine (Hiprex) Dose in Kidney Disease:

• In individuals with kidney problems, there's not much information available about how methenamine affects them.
• When it comes to mild to severe kidney issues, using methenamine is not recommended and considered unsafe.
• It's best to avoid using it in such cases to prevent any potential complications.

Methenamine (Hiprex) Dose in Liver disease:

• For people with mild to moderate liver problems, the manufacturer doesn't specify any changes in dosage in their instructions. However, it's advised to use methenamine cautiously in these cases.
• For individuals with severe liver impairment, using methenamine is not recommended and considered unsafe.

Large doses that exceed the recommended doses may result in bladder irritation resulting in dysuria, frequent and painful urination, albuminuria, and hematuria.

Side Effects of Methenamine (Hiprex):

• Dermatologic:
  • Pruritus
  • Skin rash
• Gastrointestinal:
  • Dyspepsia
  • Nausea
  • Vomiting

Contraindications to Methenamine (Hiprex):

Methenamine shouldn't be used in individuals who have:

• Hypersensitivity to methenamine or any part of the medication.
• Severe dehydration.
• Kidney problems.
• Severe liver problems.
• If they are currently receiving treatment with sulfonamides.

These conditions indicate situations where methenamine could potentially cause harm or worsen existing health issues.

Warnings and precautions

Gout

• For individuals with gout, it's best to steer clear of using methenamine because it could lead to the formation of urate crystals in the urine.
• This can worsen gout symptoms and potentially cause complications.

Hepatic impairment

• For people with liver issues, using methenamine requires caution because it can sometimes cause temporary rises in liver function tests during treatment.
• It's important to keep an eye on liver function, especially in those with liver problems.
• However, for individuals with severe liver impairment, using methenamine is not recommended due to the increased risk of complications.

Monitoring parameters:

Urinalysis:

• Your doctor may periodically check your urine to monitor for any changes, especially if you're prone to urinary tract issues.
• This helps ensure that methenamine is effectively preventing or treating infections without causing any unexpected problems.

Liver Function Tests:

• If you have liver issues or are at risk of them, your healthcare provider might conduct periodic liver function tests.
• These tests help assess how well your liver is functioning and whether methenamine treatment is affecting it.
• Monitoring liver function is crucial, especially in those with liver impairment, to catch any potential issues early on.

How to administer Methenamine (Hiprex)?

Maintaining Urine pH:

• It's important to limit alkalinizing foods and medications to keep urine pH at or below 5.5.
• This helps ensure the effectiveness of methenamine in preventing urinary tract infections.

Administration Schedule:

• Hippurate: Take twice daily, once in the morning and once at night.
• Mandelate: Take four times daily, after each meal and at bedtime. Following this schedule helps maintain consistent levels of methenamine in the body for optimal effectiveness.

Mechanism of action of Methenamine (Hiprex):

• When you take methenamine, it breaks down into formaldehyde and ammonia in acidic urine.
• Formaldehyde has the power to kill bacteria in a general way.
• Alongside methenamine, there are other parts like hippuric acid or mandelic acid that help in keeping your urine acidic.
• This acidity can also help in stopping bacteria from growing in your urine.

Absorption:

• Methenamine is readily absorbed from the gastrointestinal tract.
• However, 10% to 30% of the drug can be hydrolyzed by gastric juices unless it's protected by an enteric coating.

Distribution:

• The volume of distribution (V) is approximately 0.6 liters per kilogram of body weight, indicating that methenamine is distributed throughout the body.

Metabolism:

• Methenamine undergoes hydrolysis to formaldehyde and ammonia primarily in the urine, with approximately 10% to 25% undergoing metabolism in the liver.

Half-life Elimination:

• The half-life of methenamine is approximately 4 hours, indicating the time it takes for half of the drug to be eliminated from the body.

Time to Peak:

• Methenamine reaches peak plasma concentrations within 1 to 2 hours after administration.

Excretion:

• The primary route of excretion for methenamine is through urine, with approximately 70% to 90% of the drug being excreted unchanged within 24 hours after administration.

International Brands of Methenamine:

• Hiprex
• Mandelamine
• Antihydral
• Haiprex
• Hexamandin
• Hipeksal
• Hiprex
• Mandehexan
• Mandelamine
• Pedipur
• Reflux
• Stoppot
• Urotractan

Methenamine Brands Names in Pakistan:

No Brands Available in Pakistan.