Methenamine (By mouth)
Treats bladder and kidney infections.
When This Medicine Should Not Be Used
How to Use This Medicine
Tablet, Coated Tablet, Liquid, Granule
- Your doctor will tell you how much medicine to use and how often. Do not use more medicine or use it more often than your doctor tells you to.
- Drink plenty of water or cranberry juice every day while you are using this medicine.
- Keep using this medicine for the full time treatment time. If you stop using this medicine too soon, your infection may come back.
- Swallow the tablet or coated tablet whole with a full glass of water. Do not chew, crush, or break it.
- Measure the oral liquid with a measuring spoon or dropper. Shake the bottle before using. Take with a full glass of water or with food.
- Empty the granules into a full glass of water and let them dissolve before you drink the mixture.
If a dose is missed:
- Take the missed dose as soon as possible.
- If it is almost time for your next regular dose, wait until then to take the medicine and skip the missed dose.
- You should not use two doses at the same time.
How to Store and Dispose of This Medicine
- Store in the original tightly closed, light-resistant container, away from moisture and direct light. Do not freeze.
- Keep all medicine away from the reach of children.
Drugs and Foods to Avoid
Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.
- Make sure your doctor knows if you are also using a sulfa drug (such as Bactrim® or Septra®).
- It is best to avoid using antacids (such as Maalox® or Mylanta®) while taking methenamine.
- This medicine works best in acidic urine. Drinking cranberry juice will help keep urine acidic. Avoid foods that lower the acid in your urine, such as nuts or milk and other dairy products.
Warnings While Using This Medicine
- Check with your doctor before using this medicine if you have liver or kidney problems, severe dehydration, or other medical problems.
- If you are pregnant or breastfeeding, talk to your doctor before taking this medicine
Possible Side Effects While Using This Medicine
Call your doctor right away if you notice any of these side effects:
- Severe itching or rash
If you notice these less serious side effects, talk with your doctor:
- Mild nausea or upset stomach
- Pain when going to the bathroom (urinating)
If you notice other side effects that you think are caused by this medicine, tell your doctor
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088
- Last reviewed on 4/8/2016
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