Bactrim is an antibacterial agent. It is based on the substance trimethoprim, which is active against Gram-negative, and some gram-positive bacteria, bakteriostaticheski. The mechanism of action is associated with inhibition of the enzyme dihydrofolate reductase in the synthesis of tetrahydrofolic acid. Rapid absorption from the gastrointestinal tract and nearly complete (90-100%). Plasma protein binding is 45%. Cmax is achieved in 1-4 hours (after a single dose of about 1 mg / ml). Rapidly distributed in tissues and body fluids, including the kidney, liver, spleen sputum, saliva, semen, also found in the bile, bone marrow, the spongy, but not compact layer of the bones. The concentration in the cerebrospinal fluid is 30-50% of the concentration in the serum. Concentration in the tissues and secretions of the prostate gland is 2-3 times higher than the concentration in the serum. Bactrim dosage for adults 40-60 mg maximum daily dose of 100 mg. For children older than 1 year of 2-3 mg / kg 1 time per day. In an application with dapsone may increase concentrations of both dapsone (may increase the frequency and severity of side effects especially methemoglobinemia), and trimethoprim, which may be related to the inhibition of metabolism of dapsone and / or competition between the two drugs for excretion by the kidneys. Other folic acid antagonists (methotrexate, pyrimethamine) with simultaneous admission increases the risk of megaloblastic anemia. Bactrim inhibits hepatic metabolism of phenytoin, increasing its T1 / 2 by 50% and reducing its clearance by 30% and also reduces the renal clearance of procainamide and its metabolite N-acetyl-p-aminophenol, increasing their concentration in blood plasma. With careful use, with the possible deficiency of folic acid, aggravated allergic history, asthma, liver problems and thyroid cancer in childhood. With long-term use should be systematically study the peripheral blood, the functional state of the liver and kidneys. Elderly patients shown supplementation of folic acid.