Oral Asymptomatic bacteriuria, Treatment and prophylaxis of chronic, uncomplicated lower urinary tract infections
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.
Hypersensitivity. Gout, metabolic acidosis, severe dehydration. Renal and severe hepatic impairment. Concomitant use w/ sulfonamides or alkalinising agents.
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.
Monitor urinalysis, urine culture, LFT. Maintain an acidic urine, or give supplemental acidification (e.g. ammonium Cl, ascorbic acid, methionine), if necessary.
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.
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).
Decreased effect w/ alkalinising food.
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.
Description: 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). Pharmacokinetics: 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.
J01XX05 - methenamine ; Belongs to the class of other antibacterials. Used in the systemic treatment of infections.
Anon. Methenamine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 28/07/2017.Buckingham R (ed). Methenamine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 27/07/201.Joint Formulary Committee. Methenamine Hippurate. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 27/07/2017 .McEvoy GK, Snow EK, Miller J et al (eds). Methenamine, Methenamine Hippurate, Methenamine Mandelate. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 27/07/2017 .Methenamine Hippurate Tablets, USP 1 g (CorePharma, LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 28/07/2017.Methenamine Mandelate USP (Edenbridge Pharmaceuticals, LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 28/07/2017.