Methenamine hippurate is the generic name (meaning it is not a
brand name) of a drug that fights off bacteria in the urinary system.
Thus, methenamine hippurate is known as a urinary antibacterial
and as you may have guessed, is used to treat chronic urinary tract
infections, or those occurring suddenly. When treating suddenly
occurring infections, methenamine hippurate is never used by itself.
Methenamine hippurate is sometimes used to prevent a urinary
tract infection if instruments are going to be used to treat or
diagnose a problem in the urinary system.
HOW DOES IT WORK?
When methenamine hippurate enters the body, and is in an acidic environment, it is
changed into two colorless gases: ammonia and formaldehyde. Formaldehyde changes
the proteins that make up certain bacteria (such as E. Coli) so that their original
properties are lost. Depending on how acidic the urine is, the levels of formaldehyde may
destroy the bacteria altogether or they may only restrain their growth.
The acidity of urine is measured by the pH (potential hydrogen) level. A pH level of 7.0 is
considered neutral, below 7.0 is acidic, and above 7.0 is alkaline (opposite of acidic).
Methenamine hippurate works best when the urine is acidic (specifically, when the pH
level is 5.5 or less). One type of salt in the urine that acts to keep it acidic is hippurate.
IS METHENAMINE HIPPURATE EASILY ABSORBED?
Although methenamine hippurate is absorbed easily by the body,
acids in the stomach may make up to 60% of the drug ineffective if
the tablets are not covered with a protective layer. For
methenamine hippurate to be effective, the concentration of
formaldehyde in the urine must be greater than 25 micrograms (a
microgram is one millionth of a gram) over milliliters (one thousandth
of a liter). Methenamine hippurate is reduced to one half of its initial
amount (half-life) in 3 to 6 hours. 70-90% of methenamine hippurate
is excreted from the urine within 24 hours.
WHO SHOULD NOT USE METHENAMINE HIPPURATE?
Methenamine hippurate should not be used in individuals with severe liver damage, severe dehydration, or
WHO SHOULD BE ESPECIALLY CAREFUL WHEN USING METHENAMINE HIPPURATE?
Patients with a disease called gout should be careful when using methenamine hippurate because it may
cause crystals to separate from the urine.
WHAT ARE THE SIDE EFFECTS?
Side effects of methenamine hippurate include diarrhea, nausea and vomiting, anorexia, cramps, and
inflammation of the mouth. It can also cause skin rashes, skin eruptions, feeling itchy, headache, painful
urination, increased urine output, bladder irritation, and an increased sense of urgency to urinate. Other
side effects of methenamine hippurate include bloody urine, crystals in the urine, excess proteins in the
urine, a buildup of fluid in the body, shortness of breath, and inflammation of the lungs.
WHAT DRUGS DO METHENAMINE HIPPURATE INTEREACT WITH?
Methenamine hippurate interacts with other drugs. For example, when it interacts with medications known
as "Acetazolamide" and "Sodium bicarbonate", this will decrease the effect of methenamine hippurate
because it will interfere with the change into formaldehyde (see above). The effect of methenamine
hippurate will also be decreased if it is given along with "Thiazide diurectics" because these types of drugs
make the urine less acidic (remember that methenamine hippurate works best when the urine is more
If methenamine hippurate is given at the same time as a class of medications known as sulfonamides, this
increases the chance that crystals will form in the urine.
WHAT IS THE USUAL DOSAGE OF METHENAMINE HIPPURATE?
For children between 6 and 12 years, the dose of methenamine hippurate is generally 0.5 grams twice a
day. For children over 12 years of age and adults, the dose of methenamine hippurate is generally 1 gram
twice a day (morning and evening). Methenamine hippurate is available in tablet form.
WHAT ELSE IS METHENAMINE HIPPURATE CALLED?
Methenamine hippurate has been trademarked (given brand names) by several companies. These names
are as follows: Hiprex, Hip-Rex (based on the word "hippurate"), and Urex. By law, the brand name
versions of a generic drug all need to have the same ingredients as the generic version. The only
difference between medications with brand names and those without brand names is the price.