Classification and Pharmacokinetics
In clinical pharmacology, systemic sulfonamides are strictly categorized by their half-life ($t_{1/2}$). Sulfamethizole belongs to the short-acting drug group ($t_{1/2} < 10$ hours). This category also includes sulfanilamide (streptocide), sulfathiazole, sulfacarbamide (urosulfan), and sulfadimidine (sulfadیمیزin).
For comparison, there are intermediate-acting drugs (10–24 h, e.g., sulfamethoxazole), long-acting (24–48 h, sulfadimetoxine), and ultra-long-acting (> 48 h, sulfalene). The short half-life of sulfamethizole imposes strict dosing requirements: to maintain a therapeutic concentration in the blood, the drug must be administered frequently — 4–6 times per day.
Following oral administration, the drug demonstrates good absorption from the gastrointestinal tract, rapidly penetrating the systemic circulation and providing a resorptive effect.
Use in Urinary Tract Infections (UTIs)
Sulfamethizole is a drug of choice in the treatment of UTIs due to its unique metabolic properties.
Most sulfonamides undergo biotransformation in the liver via acetylation, converting into inactive compounds. However, sulfamethizole (like urosulfan) undergoes minimal acetylation. As a result, it is filtered by the kidneys predominantly in its free (active) form. This allows for exceptionally high active antibacterial concentrations directly within the urine, effectively eradicating infectious pathogens.
Role in the Treatment of Intestinal Infections
In treating intestinal infections (dysentery, shigellosis, gastroenteritis, enterocolitis), as well as for preventing purulent complications in intestinal surgeries, lumen-acting sulfonamides (poorly absorbed agents) are traditionally used.
However, such monotherapy has two significant drawbacks:
- Pathogens localize not only in the lumen but also invade deeply into the intestinal wall, where lumen-restricted drugs do not penetrate.
- Bacterial resistance develops rapidly to monotherapy.
To solve this problem, combination therapy is utilized. Poorly absorbed agents are combined with well-absorbed systemic sulfonamides—such as sulfamethizole or sulfadimidine. Once absorbed into the bloodstream, sulfamethizole reaches the intestinal wall "from the inside" (via systemic circulation), ensuring the eradication of intracellular and intramural bacteria.
Administration Guidelines and Concomitant Therapy
Administration of sulfamethizole requires strict adherence to rules designed to minimize adverse effects:
- Alkaline hydration: The drug is taken orally 30 minutes before meals, and each dose must be taken with ample alkaline fluids. This is a classic requirement for sulfonamides to prevent precipitation of drug crystals in the urinary tract (crystalluria).
- Vitamin supplementation: A mandatory condition for prolonged treatment is the administration of B-complex vitamins (thiamine, riboflavin, nicotinic acid). Sulfonamides suppress normal intestinal microflora, primarily Escherichia coli. This specific bacterium is responsible for the endogenous synthesis of these vitamins in the human body. Without replacement therapy, the patient will rapidly develop hypovitaminosis.
Dosing Schedule and Prescription
The standard course of treatment lasts 7–10 days and requires high starting doses to rapidly achieve therapeutic blood concentrations:
- Initial dose: 2.0 g (loading dose).
- Subsequently: 1.0 g every 4 hours.
- From the 3rd day onward: 1.0 g 4 times a day.
Example of a prescription for tablets:
Rp.: Tab. Aethazoli 0.5 D.t.d. N. 40 S. Take orally 30 minutes before meals, with ample alkaline drink. First dose 2.0 g (4 tablets), then 1.0 g (2 tablets) every 4 hours. From the 3rd day onward — 1.0 g 4 times daily.