Trimethoprim is an antibiotic used to treat the infection that causes the symptoms of cystitis. This is the same treatment that your doctor would usually prescribe for simple cystitis. In some simple cases, antibiotics won’t be prescribed and over-the-counter medicines can be used to ease the symptoms and lower the acidity of the urine
Like all medicines, trimethoprim can cause side effects. Most commonly these include nausea, vomiting, diarrhoea or an allergic rash. It is possible to be allergic to trimethoprim, and this can cause anaphylaxis and other serious problems, so you should not take trimethoprim if you are allergic to it.
This antibiotic shouldn’t be taken if you have certain blood disorders, liver or kidney problems, or if you are taking certain medicines from your doctor, such as methotrexate.
As soon as you recognise the cystitis symptoms as previously diagnosed by your doctor, you should start the course of trimethoprim provided. Take one, 200mg tablet twice a day. The tablet should be swallowed with a full glass of water at the same time each day. If the cystitis you are suffering from is caused by a bacterial infection, your symptoms should improve within a couple of days, and you should complete the course to ensure all of the infection is treated. You should also drink lots of fluid.
It is possible that your symptoms are not caused by a simple bladder infection, however. If so, the treatment provided will not improve your symptoms and they may worsen. In this case, it is very important that you visit your GP immediately to investigate the cause. You should, however, continue the course of antibiotics unless your GP directs otherwise.