methenamine

Action and Spectrum

Action

methenamine has a bactericidal effect, which means it can kill microorganisms on contact. It works well against a range of bacteria, including Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, and Enterobacter species, which can result in UTIs. Because methenamine is active in an acidic environment, it’s crucial to stay hydrated when taking this drug and maintain a low urine pH

Spectrum

Although methenamine is eliminated unchanged in urine and does not significantly accumulate in other body tissues or fluids, its range of activity is restricted to the urinary system. Methenamine is ineffective for treating systemic bacterial infections, and people with severe renal or hepatic dysfunction should not take it.

Drug Interaction

Adverse Reaction

Frequency defined 

1-10%

Nausea

Rash

Dysuria

Gastric upset

Black Box Warning

Black Box Warning:

For patients with renal impairment, the US FDA has issued a black box warning for methenamine. In patients with severe renal impairment (creatinine clearance less than 30 mL/min), phenylephrine is contraindicated because the buildup of formaldehyde in the body might result in metabolic acidosis and other harmful side effects.

Contraindication / Caution

Contraindication

Severe renal impairment: Patients with severe renal impairment (creatinine clearance less than 30 mL/min) may experience metabolic acidosis as a result of methenamine because it might cause formaldehyde to build up in the body. methenamine is therefore not recommended for these patients.

Hypersensitivity: methenamine should not be administered to patients who have a known hypersensitivity to the medication or any of its ingredients

Hepatic dysfunction: Those with hepatic impairment may be more susceptible to negative effects since methenamine is metabolized in the liver. methenamine should therefore be administered to these patients with caution.

Active urinary tract infection: Methenamine should not be used in people who have untreated infections since it is ineffective in treating current urinary tract infection

Caution

Moderate to moderate renal impairment: Individuals who have light to moderate renal impairment may be more susceptible to the body’s ability to accumulate formaldehyde. As a result, these patients should utilize methenamine with caution and have their renal function continuously evaluated during the course of treatment.

Pregnancy and lactation: Methenamine should only be taken if the possible advantages outweigh the dangers during pregnancy and breastfeeding. The drug’s safety during these times has not been verified.

Elderly Patients: Those above the age of 65 should be given methenamine with caution since they may be more susceptible to its side effects.

Patients with a history of bladder cancer: Those with a history of bladder cancer who use methenamine run the risk of developing bladder stones. Throughout treatment, these individuals should be continuously watched for the emergence of bladder stones.

Pregnancy / Lactation

Pregnancy consideration:

Pregnancy category: C

Lactation: Excreted into human milk.

Pregnancy Categories:     

Category A: Studies that were well-controlled and met expectations revealed no risk to the fetus in either the first or second trimester.

Category B: There were lack of studies on pregnant women and no evidence of risk to the fetus in animal experiments.

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.

Category D: adequate data available with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.

Category N: There is no data available for the drug under this category

Pharmacology

Pharmacology:

It works by producing formaldehyde in the urine, which has antibacterial activity against a variety of bacteria that can cause urinary tract infections. Methenamine is a medication used to treat urinary tract infections (UTIs)

Methenamine is metabolized into formaldehyde in an acidic environment after ingestion, which is created by bringing the pH of the urine below 5.5. One effective antibacterial agent is formaldehyde, which can kill bacteria by destroying their DNA and other biological components.

Pharmacodynamics:

methenamine’s conversion to formaldehyde, the urine’s active antibacterial ingredient, is a key component of its pharmacodynamics. Formaldehyde is a highly reactive substance that can attach to and harm microorganisms’ DNA and other biological components, causing their demise.

The level of formaldehyde in the urine, the length of exposure, and the susceptibility of the target bacteria are some of the variables that affect methenamine’s bactericidal activity. E. coli, Proteus mirabilis, Klebsiella pneumoniae, and several Enterobacter species are only a few of the Gram-negative and Gram-positive bacteria that can be successfully treated with methylamine.

Pharmacokinetics:

Absorption

methenamine is not absorbed from the digestive system, and it stays intact until it enters the acidic environment of the urine, when it is digested to produce formaldehyde and ammonia.

Distribution

methenamine is eliminated intact in the urine, therefore it is not disseminated to other body tissues or fluids. Furthermore, methylene blue, which is eliminated in the urine, is quickly formed from formaldehyde

Metabolism

methenamine is eliminated intact in the urine since it is not digested by the organism. 

Elimination and Excretion

methenamine is mainly eliminated in the urine as it is. The principal elimination pathway is through renal clearance, and patients with severe renal impairment should not use this medication.

Adminstartion

Administration:

For oral use, methylphenidate comes in a variety of forms, including pills, capsules, and granules. The patient’s age, weight, renal function, and the intended use all play a role in the dosage and administration of methenamine.

The typical adult dose of methenamine is 1 g (two 500 mg tablets or capsules) used twice day orally for the prophylaxis of recurrent urinary tract infections (UTIs). The length of therapy depends on the frequency and seriousness of UTIs, and the dose may be changed based on the patient’s response.

Patient Information Leaflet

Patient information leaflet

Generic Name: methenamine

Pronounced: [ meh-THEH-na-meen]

Why do we use methenamine?

methenamine is primarily used to prevent and treat urinary tract infections (UTIs), especially in individuals who experience recurrent UTIs or who are intolerant to or have contraindications to taking antibiotics.

methenamine is used as a preventive drug to stop recurrent UTIs. Those who frequently experience UTIs or who are unable to take antibiotics owing to an allergy, an intolerance, or antibiotic resistance can benefit from it the most.