Trimethoprim is the antibiotic most widely used by GPs to treat cystitis (urinary infections, urinary tract infections, UTIs). Most GPs prescribe a 3-day course of trimethoprim, although 5-day courses and even 1-day courses are sometimes prescribed.
How to order
3-day courses of trimethoprim are available from Dr Fox for women who are prone to cystitis to keep as a standby treatment for use when needed.
Approximately 90% of cystitis cases in most regions of the UK are sensitive to trimethoprim. Although bacterial resistance to trimethoprim has increased in the last decade it remains effective in most cases.

Alternatives to Trimethoprim

Alternative antibiotics are available for the treatment of urinary infections. Some doctors prefer to use these alternatives as a first choice antibiotic instead of trimethoprim. These antibiotics include quinilones (ciprofloxacin, ofloxacin, norfloxacin), amoxicillin (a type of penicillin) and nitrofurantoin. The best choice of antibiotic depends on the bacterial resistance in an area and factors such as previous responses to treatments.

When trimethoprim started to be used (since 1969) it was given combined with another antibiotic, sulfamethoxazole, in a combination tablet called co-trimoxazole (Septrim). Since 1980 trimethoprim has usually been used on its own to treat cystitis.

Trimethoprim works by blocking one of the steps in the production of DNA and thus preventing bacteria from replicating. Trimethoprim, like all antibiotics, is only effective against susceptible bacteria and has no activity against viruses.

Trimethoprim is used to treat a range of bacterial infections including respiratory and intestinal infections when it is usually taken in course of longer than 3-days. It is sometimes prescribed in low doses for continuous use to prevent recurrent urinary infections, particularly in children. Specialists and not GPs usually initiate this long-term prophylactic use of trimethoprim.

Trimethoprim side effects and cautions

Trimethoprim is usually well tolerated with most people experiencing few, minor or no side effects. The most serious side effects are allergic reactions starting soon after the first dose is taken and skin reactions ranging from minor irritation right through to generalised extreme inflammation and a rare condition known as Stevens-Johnson syndrome in which a skin rash is associated with generalised illness.

Trimethoprim should not be taken in pregnancy unless specifically recommended by a doctor. Minor and non-serious side effects include nausea, muscle aches and tummy upset (Loose stools and abdominal discomfort). People with a history of disorders of the blood, particularly people prone to anaemia and those who have had folic acid deficiency, should not take trimethoprim.

A full list of side effects and interactions with prescribed medication can be found in the trimethoprim information leaflet.

Trimethoprim is prescribed by its generic name (Trimethoprim) and not by brand name. It has been around for too long to be protected by patent or license.