This medication may interact with the following:
-Antacids
-Antihistamines for allergy, cough and cold
-Atropine
-Certain antibiotics, such as sulfacetamide, sulfamethoxazole
-Certain medications for bladder problems, such as oxybutynin, tolterodine
-Certain medications for blood pressure, such as hydrochlorothiazide
-Certain medications for depression, anxiety, or mental health conditions
-Certain medications for Parkinson disease, such as benztropine, trihexyphenidyl
-Certain medications for stomach problems, such as dicyclomine, hyoscyamine
-Certain medications for travel sickness, such as scopolamine
-Ipratropium
-Ketoconazole
-MAOIs, such as Carbex, Eldepryl, Marplan, Nardil, and Parnate
-Opioid medications for pain

They need to know if you have any of these conditions:
-Bladder or prostate problems or trouble passing urine
-Dehydration
-Glaucoma
-Heart disease
-High blood pressure
-High levels of phosphate in the blood
-High levels of sodium in the blood
-Kidney disease
-Liver disease
-Myasthenia gravis
-Sodium (salt) restricted diet
-Stomach problems
-An unusual or allergic reaction to methenamine, sodium acid phosphate, methylene blue, hyoscyamine, other medications, foods, dyes, or preservatives
-Pregnant or trying to get pregnant
-Breast-feeding

Tell your care team if your symptoms do not start to get better or if they get worse.
This medication may affect your coordination, reaction time, or judgement. Do not drive or operate machinery until you know how this medication affects you. Sit up or stand slowly to reduce the risk of dizzy or fainting spells. Drinking alcohol with this medication can increase the risk of these side effects.
Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water may help. Contact your care team if the problem does not go away or is severe.
You may need to be on a special diet while taking this medication. Ask your care team how many glasses of fluids you need to drink each day. Also, ask which foods to include and which to avoid to help keep your urine acidic. Your urine must be acidic for this medication to work.
This medication may cause dry eyes and blurred vision. If you wear contact lenses, you may feel some discomfort. Lubricating drops may help. See your eye care team if the problem does not go away or is severe.

Keep out of the reach of children and pets.
Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Get rid of any unused medication after the expiration date.
To get rid of medications that are no longer needed or have expired:
-Take the medication to a medication take-back program. Check with your pharmacy or law enforcement to find a location.
-If you cannot return the medication, check the label or package insert to see if the medication should be thrown out in the garbage or flushed down the toilet. If you are not sure, ask your care team. If it is safe to put it in the trash, empty the medication out of the container. Mix the medication with cat litter, dirt, coffee grounds, or other unwanted substance. Seal the mixture in a bag or container. Put it in the trash.