methenamine (Mandelamine, Hiprex, Urex)
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Introduction
Tradenames: Mandelamine, Hiprex, Urex.
Indications
- used after erradication of bacterial infection to prevent or eliminate frequently occurring urinary tract infections[4]
Contraindications
- avoid in patients with creatinine clearance < 40 mL/min
Dosage
Tablet: as hippurate (Hiprex, Urex) 1 g
Tablet: as mandelate (Mandelamine) 500 mg, 1 g.
Pharmacokinetics
- 10-20% metabolized by the liver
- 1/2life is 3-6 hours
- 90% eliminated in the urine
- decreased effects are observed in patients with non-acidic urine
elimination via kidney
elimination via liver
Antimicrobial activity
Most strains of Proteus, Pseudomonas & Enterobacter are resistant.
Adverse effects
- not common (1-10%)
- uncommon (< 1%)
- headache, elevated liver function tests, hematuria, bladder irritation, dysuria, crystalluria, gout
Drug interactions
- sulfa drugs may precipitate in renal tubules when used in combination
- milk, bicarbonate, acetazolamide inhibit hydrolysis of methenamine to bactericidal metabolites NH3 & formaldehyde by alkalinizing urine
Mechanism of action
- mandelate lowers urinary pH
- methenamine is hydrolyzed to ammonia plus formaldehyde in the distal renal tubule which are bactericidal[4]
More general terms
Component of
- methenamine/sodium phosphate
- mandelic acid/methenamine/phosphate/sodium phosphate
- hyoscyamine/methenamine/methylene blue/sodium phosphate
- hyoscyamine/methenamine/methylene blue/phenyl salicylate/sodium phosphate
- hyoscyamine/methenamine/methylene blue/phenyl salicylate
- benzoic acid/hyoscyamine/methenamine/methylene blue/phenyl salicylate
- atropine/benzoic acid/hyoscyamine/methenamine/methylene blue/phenyl salicylate
- hyoscyamine/methenamine/methylene blue/phenyl salicylate/salicylate/sodium phosphate
- benzoate/hyoscyamine/methenamine/methylene blue/phenyl salicylate
- mandelic acid/methenamine/sodium phosphate
- methenamine/salicylate
- hyoscyamine/methenamine/methylene blue/salicylate/sodium phosphate
- hyoscyamine/methenamine/methylene blue/salicylate
References
- ↑ Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
- ↑ The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996
- ↑ Kaiser Permanente Northern California Regional Drug Formulary, 1998
- ↑ 4.0 4.1 4.2 Harding C, Forbes R, Currer S et al. Alternative to prophylactic antibiotics for the treatment of recurrent urinary tract infections in women: Multicentre, open label, randomised, non-inferiority trial. BMJ 2022 Mar 9; 376:e068229. PMID: https://www.ncbi.nlm.nih.gov/pubmed/35264408 Free article