The active substance trimethoprim is an antibiotic that belongs to the category of diaminopyrimidines. The drug is used in the treatment of infections caused by bacteria. The drug trimethoprim is especially frequently used for the treatment of cystitis in female patients. As a rule, the drug is taken in the morning and evening after meals. In this case, the average duration of therapy is between three and five days.
What is trimethoprim?
The drug is used in the treatment of infections caused by bacteria. Trimethoprim is an active substance from the group of antibiotics and is used in many cases in combination with the substance sulfamethoxazole. The possible undesirable side effects are similar to those that sometimes occur with other types of antibiotics. Very often, for example, symptoms such as nausea and vomiting, fever and diarrhea, as well as disturbances of the blood count, appear in the course of therapy. The active ingredient trimethoprim is usually available on the market in tablet form and as a liquid syrup. So-called generics are also sold. From a chemical point of view, the substance trimethoprim is trimethoxybenzylpyrimidine. It has a molar mass of 290.3 grams per mole. The substance is a white to yellowish powder and shows low solubility in water.
Pharmacological action
The drug trimethoprim is characterized primarily by a bacteriostatic effect. This is because the substance inhibits the so-called dihydrofolate reductase, so that the metabolism of folic acid is impaired in Gram-negative and Gram-positive bacteria. If the substance is used alone and not in combination with other active ingredients, uncomplicated urinary tract infections or upper respiratory tract infections are often the cause. Basically, the drug trimethoprim impairs the dihydrofolate reductase of bacteria. In this process, dihydrofolic acid is converted into tetrahydrofolic acid. Tetrahydrofolic acid plays an important role for the cells of bacteria as a substrate necessary for the formation of thymidine and purines. If these special building blocks of DNA are not present, the growth of bacterial cells is impaired. In this context, trimethoprim usually has only minor effects on dihydrofolate reductase in humans. In principle, the spectrum of activity of the substance trimethoprim extends to a large number of gram-positive as well as gram-negative pathogens. It should be noted, however, that resistance to antibiotics develops quite rapidly during therapy with trimethoprim alone. When administered orally, the substance trimethoprim is absorbed relatively quickly. Approximately two hours after administration, the active substance reaches its highest concentration in the serum. The half-life is about twelve hours. The drug trimethoprim is metabolized hepatically and subsequently excreted renally. Therefore, it is important to note that in the presence of renal impairment, the metabolites of the drug may accumulate.
Medical use and application
The drug trimethoprim is relatively rarely used as part of monotherapy. Instead, it is usually used in conjunction with the substance cotrimoxazole as a so-called fixed combination, using the active ingredient sulfamethoxazole. If trimethoprim is combined with the active substance sulfamethoxazole, the possible area of application is also expanded. The substance sulfamethoxazole belongs to the sulfonamide category. In combination with trimethoprim, treatment of Toxoplasma gondii or Pneumocystis jirovecii is possible. At the same time, however, the spectrum of potential side effects expands. The combination of the active ingredients trimethoprim and sulfamethoxazole is known as cotrimoxazole. This compound is also suitable, for example, for the treatment of the autoimmune disease granulomatosis with polyangiitis. Pneumocystis pneumonia is a special indication. In this case, cotrimoxazole must be taken in high doses over a longer period of time. In the context of monotherapy, the administration of trimethoprim is possible, for example, in uncomplicated cystitis and for the prevention of recurrent urinary tract infections in children. In principle, however, monotherapy with the active ingredient trimethoprim is the subject of critical debate.
Risks and side effects
In the course of therapy with the drug trimethoprim or combination preparations containing this active substance, various undesirable side effects and complaints are possible. These occur with varying frequency and vary depending on the individual case. In most cases, trimethoprim is a well-tolerated preparation. In some cases, however, gastrointestinal complaints occur. Itchy exanthema is also possible. In rare cases, the drug inhibits the important dihydrofolate reductase in humans, resulting in a deficiency of tetrahydrofolic acid. This disrupts hematopoiesis, resulting in anemia, thrombocytopenia, or leukopenia. In addition, some patients experience rashes on the skin, sometimes associated with itching. More rarely, serious skin irritations or Lyell’s syndrome occur. Aseptic meningitis is also possible in the course of taking trimethoprim. Patients sometimes suffer from fever and blood count disturbances are seen. Very rarely, phototoxic reactions and inflammation of the pancreas occur. The drug trimethoprim interacts with some substances and should therefore not be taken simultaneously with them. These include, for example, antidiabetics, oral contraceptives, diuretics, ciclosporin and indomethacin. If symptoms occur during therapy, consult a physician immediately.
