Methenamine hippurate microbiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Abdurahman Khalil, M.D. [2]
Methenamine hippurate USP has antibacterial activity because the methenamine component is hydrolyzed to formaldehyde in acid urine. Hippuric acid, the other component, has some antibacterial activity and also acts to keep the urine acid. The drug is generally active against E. coli, enterococci and staphylococci. Enterobacter aerogenes is generally resistant. The urine must be kept sufficiently acid for urea-splitting organisms such as Proteus and Pseudomonas to be inhibited
References
http://www.accessdata.fda.gov/drugsatfda_docs/label/2005/17681s014lbl.pdf