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Pharmacy and Medications




Is methenamine a prescription medication? I bought an OTC medication for a UTI and this was listed as one of the ingredients (the other one was aspirin). But when I looked this ingredient up on the Internet the info I found says it is a prescription drug.


Methenamine has an FDA labeled indication for the treatment or prevention of recurrent urinary tract infections or urinary tract discomfort.  This medication is considered an antibiotic and works by forming compounds in the body, more specifically in the urine, to suppress bacterial growth and increase urine acidity to help get rid of bacteria causing the UTI.

Methenamine is considered a prescription medication, but at much higher doses than what is contained in OTC products.  For example, methenamine used in a hospital setting or as a prescription medication has a dosage of 1 gram, two to four times daily.  In an OTC product, such as Cystex┬« (containing aspirin, benzocaine, and methenamine), the dosage is equivalent to 162.5 milligrams of methenamine four times a day.  So, the amount of methenamine in over-the-counter products is less than the amount in a prescription from a physician. 

In conclusion, methenamine could be viewed as a prescription medication or an OTC medication.  Large doses (usually 1gram or more) of the medication are considered prescription only, whereas low doses of methenamine (usually 160-170 milligrams) are considered an OTC product and do not require a prescription. Although this medication is an antibiotic used for the treatment of urinary tract infections, an OTC medication containing methenamine will not cure a UTI.  The low dose of methenamine contained in OTC medications is solely used to help prevent the progression of infection until you can see a doctor. 

Submitted by John Mallett, PharmD Candidate

Ohio Northern University College of Pharmacy

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Response by:

Carmen M Hadley, RPh, CSPI
Former Clinical Instructor
College of Pharmacy
The Ohio State University