Methenamine
Methenamine is a widely used ingredient in cosmetics, personal care, and skincare formulations. Depending on its function, it may serve as a moisturizer, preservative, emulsifier, or active ingredient to enhance the overall effectiveness and performance of a product.
Methenamine, also known as hexamine or hexamethylenetetramine and sold under the brand names Hiprex, Urex, and Urotropin among others, is a urinary tract antiseptic and antibacterial medication which is used in the prevention of recurrent urinary tract infections (UTIs). It is not an antibiotic, and unlike antibiotics, has no risk of bacterial resistance. Methenamine can reduce the risk of UTIs by 44 to 86% and has been found to be non-inferior to low-dose prophylactic antibiotics. It is taken by mouth. The drug is available both by prescription and at lower doses over the counter. Besides for UTI prevention, methenamine is also available in a topical form to treat hyperhidrosis.
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| Pronunciation | meh-THEH-na-meen |
| Trade names | Antihydral, Hiprex, Urex, Urotropin, others |
| Other names | Hexamethylenetetramine; HMTA; Hexamine; Hexamethylenamine; Hexamethyleneamine; Metenamine; Urometine; Hippramine; E-239; R-657; 1,3,5,7-Tetraazaadamantane |
| Routes of administration | Oral, topical |
| Drug class | Antiseptic; Antibacterial |
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| Bioavailability | High (≥70%) |
| Protein binding | Unknown |
| Metabolism | Hydrolysis in acidic urine |
| Metabolites | • Formaldehyde • Ammonia • Formic acid |
| Onset of action | ≤30 minutes |
| Elimination half-life | 2–6 hours |
| Excretion | Urine: 70–90% unchanged within 24 hours |
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| Formula | C6H12N4 |
| Molar mass | 140.190 g·mol−1 |
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Side effects of methenamine are generally minor and include upset stomach, nausea, and headache, among others. Methenamine is a prodrug of formaldehyde in acidic urine. Formaldehyde is a non-specific antiseptic and bactericide which works via denaturation of bacterial proteins and nucleic acids. Conversion of methenamine into formaldehyde only occurs in acidic environments and hence its actions show selectivity for tissues like the bladder and stomach. Chemically, methenamine is a simple cyclized hydrocarbon and is similar in structure to adamantane.
Methenamine was discovered in 1859 and was first introduced for medical use as a urinary antiseptic in 1895. It was formally approved for medical use in the United States in 1967. Though it became a "forgotten drug" following the discovery of antibiotics in 1928, there has been a resurgence in interest in methenamine since 2010 owing to increasing rates of bacterial resistance with antibiotics. Larger and higher-quality clinical trials of methenamine for UTI prevention have started to be published in the 2020s and it may soon be recommended by more medical guidelines. Methenamine has been found to be more cost-effective than low-dose prophylactic antibiotics for preventing UTIs.
