Dr Sharon Rees @reesprescribe
Day 1: #methenamine hippurate is an oral urinary antiseptic discovered in 1859. It has a wide antibacterial spectrum & popularity has been revived because of resistance to UTI antibiotics. Active infection is first cleared with antibiotics & methenamine can then be used if needed for ongoing antibacterial activity is needed
Dr Sharon Rees @reesprescribe
Day 2: #methenamine tablet is licensed in adults & children over 6yrs for prevention of simple lower UTIs. Dose over 12 yrs of age is 1g x2/day or for catheterised adults x2-3/day. Can lead to acid crystal formation, so severe dehydration, Cr Cl<10mls/min & gout are all contra-indicated
Dr Sharon Rees @reesprescribe
Day 3: #methenamine has good GI tract absorption, cmax 1-2 hrs. Highly soluble in water & antibacterial effects begin 30 mins after taking. Decomposes to formaldehyde & ammonia in the urinary tract. If liver impairment, risk of ammonia metabolite accumulation. Renal excretion. T ½ ~4hrs
Dr Sharon Rees @reesprescribe
Day 4: In salt form, the 2 components of #methenamine hippurate are both active. The hippuric acid delivers acidity as, in acidic conditions #methenamine decomposes to formaldehyde. This is a strong antibacterial agent > denaturing bacterial proteins. Hippuric acid also has minor bacteriostatic properties
Dr Sharon Rees @reesprescribe
Day 5: Adverse drug effects for #methenamine hippurate. Uncommon include gastric irritation, irritation of the bladder, dysuria, nausea, vomiting, rash pruritis. Unknown frequency diarrhoea and abdominal pain (NOT exhaustive)
Dr Sharon Rees @reesprescribe
Day 6: #methenamine drug-drug interactions; crystalluria risk increases with use of sulphonamides (severe). Alkalising agents & acetazolamide can decrease efficacy. Can affect urine specimen results (NOT exhaustive)
Dr Sharon Rees @reesprescribe
Day 7: Evidence supports use in UTI prevention as equivalent to antibiotics with good safety/tolerance. #methenamine hippurate can be used long term.1 month standard treatment £16 (UK drug tariff). This is a higher cost compared to standard prophylactic antibiotics but there are benefits for anti-microbial resistance
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In addition to the posts, read the BNF monograph on methenamine hippurate and the related treatment summary on ‘Urinary tract infections’. Another useful source is the Summary of Product Characteristics for methenamine hippurate, see links below. Once you have completed this, answer the 10 questions. Submit your answers to reesprescribe@gmail.com. If you answer at least eight out of 10 questions correctly, you will receive your CPD certificate via email.
- Methenamine is an antibiotic drug TRUE or FALSE?
- Methenamine is licensed in those over 6 years old TRUE or FALSE?
- Which of the following is TRUE?
- Methenamine is used for complicated UTIs
- Methenamine is used to prevent complicated UTIs
- Methenamine is used to prevent recurrence of uncomplicated UTIs
- Methenamine is used just for catheter associated UTIs
- Methenamine is always used alongside antibiotics TRUE or FALSE?
- Methenamine requires the urine to be acidic in order to work TRUE or FALSE?
- Which of the following is FALSE?
- Formaldehyde is a weak disinfectant
- Ammonia is a metabolite of methenamine
- Methenamine can encourage uric acid crystal formation
- Methenamine should be avoided in liver impairment
- Methenamine has lots of common side-effects TRUE or FALSE?
- Methenamine may be used for short or long-term treatment TRUE or FALSE?
- Methenamine is helpful to limit the amount of antibiotics used for UTIs TRUE or FALSE?
- Methenamine is a low-cost option compared to antibiotics TRUE or FALSE?
Further reading on #methenamine
- https://bnf.nice.org.uk/drugs/methenamine-hippurate/
- https://bnf.nice.org.uk/treatment-summaries/urinary-tract-infections/
- https://www.medicines.org.uk/emc/product/12707/smpc#gref