UTI Prophylaxis: Does Methenamine Hippurate Work?

An updated intervention review of the use of methenamine hippurate for the prevention of urinary tract infections (UTIs) has found that methenamine may effectively prevent UTIs in certain patient populations.¹
 
Methenamine hippurate is often used as an alternative to antibiotics for the prevention of UTI in patients at risk for recurrent UTI. To assess the benefits and harms of methenamine hippurate for the prevention of UTI, researchers identified randomized controlled trials and quasi-randomized controlled trials that compared groups of patients who used methenamine with groups of patients who did not use methenamine. Thirteen studies involving 2032 participants were included in the analysis, of which 6 studies reported symptomatic UTI and 8 studies reported bacteruria. The authors described the study quality as mixed and stated that the underlying heterogeneity of the 13 studies evaluated made it impossible to interpret the overall pooled estimates for the major outcome measures.

In patients without renal tract abnormalities, methenamine hippurate may be beneficial for patients at risk for recurrent UTIs, according to the results of a subgroup analysis. When symptomatic UTI was reported, patients who took methenamine were 76% less likely to have a UTI than patients who took placebo or had no prophylactic treatment. Also in this study group (symptomatic UTI) and compared with patients who did not use methenamine, use of methenamine for 7 days or less was associated with an 86% reduction in risk of UTI in patients without renal tract abnormalities. When bacteruria was reported, patients who used methenamine were 44% less likely to have a recurrent UTI. It was also determined that methenamine has no prophylactic effect in patients with neuropathic bladder. The reported rates of adverse events were low but poorly described. Prescribing information cites nausea, vomiting, dysuria, and rash as the most common adverse effects of methenamine.²
 
The review authors suggest that their results be interpreted cautiously. Despite these new findings, there is insufficient evidence to support the routine use of methenamine hippurate for the prevention of UTIs. Although patients without renal tract abnormalities rarely experience the serious complications that are associated with repeated UTIs, in patients with renal tract abnormalities, such as scarring that causes renal hypertension and possibly eventual renal failure, they are at risk for antibiotic resistance associated with long-term or repeated use of antibiotics. A better understanding of the effectiveness of long-term use of methenamine is needed.

Pertinent Points:
- Methenamine hippurate may effectively prevent UTIs in patients with no abnormalities of the renal tract.
- Additional large, well-designed randomized controlled trials are needed to determine the effectiveness of long-term use of methenamine in patients without neuropathic bladder.

References:

1. Lee BSB, Bhuta T, Simpson JM, Craig JC. Methenamine hippurate for preventing urinary tract infections. Cochrane Database System Rev. 2012;10. DOI: 10.1002/14651858.CD003265.pub3.
2. Methenamine. Available at: http://www.drugs.com/pro/methenamine.html. Accessed November 10, 2012.