After oral administration after 30 minutes is detected in the blood, the period of maximum concentration is 8-12 hours.Unlike other representatives of long-acting sulfonamides, it penetrates poorly through the blood-brain barrier and its concentration in the cerebrospinal fluid is low. However, with the inflammation of the meningeal membranes, the permeability of the blood-brain barrier sharply increases. Therapeutic concentration in adults is noted when taking 1-2 g in the first day and 0.5-1 g in the following days. The drug accumulates in the blood, primarily due to the high degree of binding to blood proteins (90 -99%). Well distributed to organs and systems. It penetrates well into the pleural fluid (60-90% of the concentration in the blood), in the biliary system, where its concentration is 1.5-4 times higher than in the blood. Unlike other sulfonamides, the preferential metabolism is carried out along the path of microsomal glucuronation, NADP-H-dependent and associated with cytochrome P450.
It is withdrawn slowly, first of all, due to plasma retention in the blood and due to a high degree of reabsorption in the tubule of the kidneys (93-97.5%). The blood contains 5-15% of acetylated metabolites, in urine - 10-25% of acetyl derivatives and 75-90% of glucuronide sulfadimethoxin; the latter is readily soluble and does not provoke the development of crystalluria. The acetyl derivative is not reabsorbed and is completely excreted by the kidneys.After 24 hours, 20-44% of the dose given is taken out, after 48 hours - up to 56%, after 96 hours - up to 83.3%.