Trimethoprim

What is Trimethoprim?

Trimethoprim is a broad use antibiotic that comes as an oral tablet. It’s used to treat lots of different bacterial infections, and is often used to treat cystitis, a common UTI.

Cystitis is an inflammation of the bladder, usually caused by bacteria. It mostly affects women, with around 50% of women suffering from cystitis by age 32.^[1] It can also affect men, but it’s a lot less common. It can clear up on its own but for persistent and severe symptoms it may require antibiotics, such as Trimethoprim.

How does Trimethoprim work?

Trimethoprim is a type of antibiotic that prevents the growth of bacteria. Bacteria requires a substance called folate in order to grow. Trimethoprim stops bacteria from producing folate, and this prevents the bacterial cells from duplicating themselves as they cannot produce DNA.

Because the bacteria can no longer grow and spread, your body’s own immune system can clear up the remaining infection by destroying any bacteria that are left.

What doses of Trimethoprim are there?

Trimethoprim comes in two doses, either 100mg or 200mg. The dosage you’re prescribed will depend on the severity and nature of your symptoms, your age, and how well your kidneys work.^[2]

How to take Trimethoprim

For instructions on specific dosages, you should always refer to the package information leaflet or the advice of your clinician. Please note Trimethoprim is not suitable for children under 6.

To take Trimethoprim, swallow one tablet with a glass of water. If you’re taking multiple tablets a day, try to take them around the same time each day.

Usually, your doses will be as follows:

200mg twice a day for three days for women and seven days for me.

How long does it take Trimethoprim to work?

You should see an improvement in your symptoms within 24 hours, and your infection should continue to clear up during the remaining course of your Trimethoprim. But if you see no improvement after the first 48 hours of starting your medication, you should send our clinician a message and speak to them about the next steps.

You should always continue the course of treatment as advised, even if you start to feel better before it’s finished. Although it may appear that the treatment has fully worked, there may be some residual bacteria remaining, which can become resistant to the antibiotic and cause problems further down the line.

What should I do if I make a mistake when taking Trimethoprim?

You should always use Trimethoprim exactly as your clinician tells you. If you accidentally miss a dose, then you can simply take it when you remember – as long as it is not too close to your next dose. If it is, take the tablet you missed when you would take your next dose, and carry on as normal for the rest of the course. Never attempt to ‘double up’ on doses to make up for a missed dose.

If your day to day activities keep you very busy, it may be helpful to set an alarm on your phone or alarm clock to remind you to take your medication.

If you take too much Trimethoprim, you should seek medical assistance immediately.