Methenamine - oral

Patient Medicine Information
Why do I need this medicine?
Methenamine is used in the treatment and prevention of bacterial infections of the bladder.

This medicine may be used to treat other conditions as decided by your doctor.
How do I take this medicine?
Take Methenamine exactly as directed by your doctor or according to the instructions on the label. Do not take more or less than instructed by your doctor.

If you have difficulty swallowing tablets, you may crush the tablets and mix it with glass of water, milk, or fruit juice. Stir and drink immediately.

Methenamine must be taken at regular intervals as instructed. Continue to take this medicine even when you feel better. Do not stop taking it unless instructed by the doctor.

Do not skip any doses. You must complete the entire course of antibiotic. If you don't, the infection will not clear completely.
What should I do if I have forgotten to take this medicine?
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and return to your normal dosing schedule.

DO NOT double a dose under any circumstances.

If you often forget to take your medicine, let your doctor and pharmacist know.
When should I not use this medicine?
Do not take Methenamine if you have a history of allergic reactions (swollen eyes or mouth, difficulty breathing, rashes) to this medicine.

Alert your doctor if you have the following conditions:

- severe dehydration
- severe liver disease
- kidney disease
as Methenamine may not be suitable for you.

DO NOT take Methenamine if you are currently taking a certain type of antibiotic called sulfonamides e.g. sulfadiazine, sulfamethoxazole, sulfadoxine, sulfisoxazole.
What should I take note of while taking this medicine?
Inform your doctor if you have gout (abnormal metabolism of uric acid) or liver disease.

Let your doctor know if you are pregnant or breastfeeding.

For as long as you are taking Methenamine, you may need to have urine tests and liver function tests to check your body's response to the medicine. Your doctor will advise you about how often you need to have these tests.
What side effects could I experience?
Methenamine may cause any of the following side effects: stomach upset, nausea, vomiting, painful and difficult urination, rashes and itching of the skin.

Inform your doctor if any of these side effects do not go away or are severe, or if you experience other side effects.
Can I take this with other medicines?
DO NOT take Methenamine if you are currently taking a certain type of antibiotic called sulfonamides e.g. sulfadiazine, sulfamethoxazole, sulfadoxine, sulfisoxazole.

Inform your doctor and pharmacist if you are taking any of these medicines:

- medicines for decreasing the acidity of urine e.g. potassium citrate
- medicines for neutralising stomach acid e.g. calcium carbonate, aluminium hydroxide, magnesium hydroxide
- medicines for water retention (water pills) e.g. chlorothiazide
- medicines for glaucoma (increased pressure in the eyes) e.g. acetazolamide

This list does not include all medicines that may interact with Methenamine.

Always notify your doctor and pharmacist if you are taking any other medicines, including herbal tonics such as traditional Chinese medicines, supplements and medicines that you buy without a prescription.
What special dietary instructions should I follow?
Your doctor may advise you to drink cranberry juice while you are being treated with Methenamine. This will help improve the absorption of the medicine.

Avoid taking Methenamine together with foods that may decrease the acidity of urine such as wheat grass, cucumber, broccoli, soy beans and avocado. Ask your doctor about the types of food you should avoid.

Avoid alcohol.
How should I store this medicine?
Store in a cool, dry place away from the reach of children.

Medicines must not be used past the expiry date.
This information is independently developed by MIMS based on methenamine - oral and is provided for your reference only. It is not a replacement for and should only be used in conjunction with full consultation with a licensed healthcare professional, the information provided by your pharmacist and/or the manufacturer of the medication. It may not contain all the available information you require and cannot substitute professional medical care, nor does it take into account all individual circumstances. Although great effort has been made to ensure content accuracy, we shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2022 MIMS. All rights reserved. Powered by
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