Co-trimoxazole

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Cotrimoxazole is a combination preparation of two proven antibiotics from the group of folic acid antagonists. It helps particularly well with infections of the urinary tract, the gastrointestinal tract or the upper and lower respiratory tract. Here you can read everything you need to know about the mode of action, side effects and use of co-trimoxazole.

This is how cotrimoxazole works

Cotrimoxazole is a combination preparation of the antibiotics sulfamethoxazole and trimethoprim. Both substances inhibit the formation of folic acid in certain bacteria and fungi. This is required for the synthesis of some building blocks of the genetic material (thymidine and purines). Cotrimoxazole interrupts folic acid synthesis in two different ways.

Sulfamethoxazole prevents the formation of a folic acid precursor (dihydrofolic acid) by binding to the enzyme responsible for it (dihydropteroic acid synthetase) and overriding it. Since this mechanism is reversible, high sulfonamide concentrations are required at all times.

Trimethoprim in turn inhibits the enzyme dihydrofolic acid reductase, which converts the folic acid precursor into the end product, tetrahydrofolic acid. This also stops the formation of the DNA building blocks and prevents the bacteria from multiplying.

Co-trimoxazole works best when the two active ingredients are present in the body in a concentration ratio of 5: 1 (sulfamethoxazole: trimethoprim). The supporting effects of the two preparations increase the effectiveness, expand the spectrum of activity and delay the development of bacterial resistance to the antibiotic.

When is co-trimoxazole used?

Co-trimoxazole is particularly often used for bacterial urinary tract infections. It also helps with infections of the upper and lower respiratory tract, the female and male genitals, or the gastrointestinal tract.

This is how cotrimoxazole is used

Co-trimoxazole can be prescribed as a juice, solution or tablet with various concentrations of the active ingredient. For adults and adolescents aged 13 and over, the average dose is 720 to 960 milligrams of the active ingredient combination per day. The cotrimoxazole is best taken in the evening. Children from six to twelve years of age should take one tablet containing 480 milligrams of co-trimoxazole twice a day. For the treatment of pneumonia caused by fungi (Pneumocystis jiroveci) in patients with immunodeficiency, the dose should be four times higher.

The duration of the therapy depends on the severity of the disease and the course of the disease. Treatment usually lasts five to eight days.

What are the side effects of co-trimoxazole?

Common side effects are allergic reactions of the skin, which can manifest as itching (pruritus) or rash (exanthema). Symptoms of the gastrointestinal tract such as pain in the upper abdomen, loss of appetite, nausea, vomiting and diarrhea are also possible.

Occasional side effects can include increased or decreased potassium levels in the blood, liver dysfunction (cholestatic hepatosis) and tinnitus.

Very rarely, after the use of co-trimoxazole, a decrease in the number of blood platelets (thrombocytopenia), white blood cells (neutropenia) and an increase in liver enzymes are found in the blood. These side effects are more common in patients over 60 years of age.

Taking antibiotics such as co-trimoxazole can affect the effectiveness of oral contraceptives (pill). In general, therefore, if you take the pill, you should use a mechanical contraceptive method, such as condoms, during antibiotic treatment and for seven days afterwards or until after the end of the next pill break, to be on the safe side.

When should you not take cotrimoxazole?

Patients should not take co-trimoxazole if they have already had an allergic reaction to the active substance. Use should also be avoided if the patient has severe liver or kidney damage or a thyroid dysfunction. Even in the case of changes in the blood count or a possible folic acid deficiency, the cotrimoxazole can interact with other drugs that are used at the same time and thus increase or lose its effect. The simultaneous use of local anesthetics (such as benzocaine), gastric acid-regulating substances (mineral antacids) and the sedative paraldehyde should be avoided, as these drugs reduce the effect of co-trimoxazole.

Co-trimoxazole works more than intended if drugs are taken at the same time that make urination easier (e.g. probenecid) or those that are non-steroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or acetylsalicylic acid).

Expectant mothers should not take the active ingredient during pregnancy, as there has not been sufficient research into how cotrimoxazole affects the fetus. In premature babies and newborns, there is a risk of jaundice (jaundice), which is why they are not treated with the active ingredient.