Methenamine


Full Prescribing Info
Dosage/Direction for Use

Oral
Treatment and prophylaxis of chronic, uncomplicated lower urinary-tract infections., Asymptomatic bacteriuria
Adult: As methenamine hippurate: 1,000 mg bid. In catheterised patient: 1,000 mg tid. As methenamine mandelate: 1,000 mg 4 times daily.
Child: <6 yr As methenamine mandelate: 18 mg/kg 4 times daily; 6-12 yr As methenamine hippurate: 500-1,000 mg bid; As methenamine mandelate: 500 mg 4 times daily; >12 yr
: As methenamine hippurate/mandelate: Same as adult dose.
Renal impairment:
Contraindicated.
Hepatic impairment: Severe: Contraindicated.
Contraindications
Hypersensitivity. Gout, metabolic acidosis, severe dehydration. Renal and severe hepatic impairment. Concomitant use w/ sulfonamides or alkalinising agents.
Special Precautions
Patient w/ indwelling urinary catheters; conditions wherein urine acidification is contraindicated or unattainable (e.g. presence of urea-splitting bacteria in the urine). Mild to moderate hepatic impairment. Childn. Pregnancy and lactation. Not intended for use in upper UTI. Monitoring Parameters Monitor urinalysis, urine culture, LFT. Maintain an acidic urine, or give supplemental acidification (e.g. ammonium Cl, ascorbic acid, methionine), if necessary.
Adverse Reactions
Significant: Increased ALT/AST, dysuria. GI: Dyspepsia, nausea, vomiting, diarrhoea. Genitourinary: Bladder irritation, painful/frequent micturition, albuminuria, haematuria. Dermatologic: Rash, pruritus.
Overdosage
Symptoms: Vomiting, haematuria. Management: Immediately induce emesis or perform gastric lavage. Maintain adequate hydration, give copious quantities of water and 2-3 teaspoonfuls of Na bicarbonate.
Drug Interactions
Acetazolamide may inhibit conversion of methenamine into formaldehyde.
Potentially Fatal: Risk of crystalluria when given w/ sulfonamides (e.g. sulfamethizole) or urinary alkalinising agents (e.g. potassium citrate).
Food Interaction
Decreased effect w/ alkalinising food.
Lab Interference
May interfere w/ determination of urinary catecholamines and vanillylmandelic acid (VMA) using fluorometric procedures, and 17-hydroxycorticosteroid using Porter-Silber method, resulting in falsely high results. May falsely decrease 5-hydroxyindoleacetic acid (5HIAA) levels when using nitrosonaphthol methods, and estriol levels when using acid hydrolysis techniques.
Action
Methenamine is a urinary antibacterial agent. Its action depends on its conversion in acidic urine into formaldehyde, a nonspecific bactericidal agent, that is active against both gram+ve and gram-ve bacteria.
Onset: W/in 30 min (as hippurate).
Absorption: Readily absorbed from the GI tract. Time to peak plasma concentration: 1-2 hr.
Distribution: Widely distributed in the body. Crosses the placenta and enters breast milk. Volume of distribution: 0.6 L/kg.
Metabolism: Undergoes hydrolysis in the urine at pH ≤5.5 into ammonia and formaldehyde. Approx 10-25% is metabolised in the liver.
Excretion: Via urine (approx 70-90%, as unchanged drug). Elimination half-life: Approx 4 hr.
Storage
Oral: Store between 15-30°C.
CIMS Class
ATC Classification
J01XX05 - methenamine ; Belongs to the class of other antibacterials. Used in the systemic treatment of infections.
Disclaimer: This information is independently developed by CIMS based on methenamine from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to CIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, CIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 CIMS. All rights reserved. Powered by CIMSAsia.com
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