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Sulfamethizole is a short-acting antibacterial sulfonamide.



Sulfamethizole shares the actions and uses of the other antibacterial sulfonamides. Sulfamethizole is used principally in the treatment of urinary tract infections caused by sulfonamide-susceptible organisms. Blood concentrations of sulfamethizole are too low to use the drug in the treatment of urinary tract infections with systemic involvement or in the treatment of systemic infections.


Dosage and Administration


Sulfamethizole is administered orally.


The usual adult dosage of sulfamethizole is 0.5-1 g administered 3 or 4 times daily. In children older than 2 months of age, the usual dosage of sulfamethizole is 30-45 mg/kg daily administered in 4 equally divided doses.


Sulfamethizole shares the toxic potentials of the sulfonamides, and the usual precautions of sulfonamide therapy should be observed, including maintenance of adequate fluid intake to reduce the risk of crystalluria.



Sulfamethizole is readily absorbed from the GI tract. Following oral administration of a single 2-g dose of sulfamethizole in a limited number of patients, blood concentrations of approximately 30 mcg/mL were attained within 1 hour. Peak blood concentrations of about 60 mcg/mL were reached within 2 hours followed by a gradual decrease to 6.6 mcg/mL within 8 hours and to 5 mcg/mL within 12 hours. Approximately 2-11% of sulfamethizole present in blood is in the N 4-acetylated form.


Sulfamethizole is distributed into most body tissues but does not appear to diffuse into the CSF of patients with normal meninges. Sulfamethizole is approximately 90% bound to plasma proteins. Since the drug is rapidly eliminated in urine, the manufacturers state that accumulation of sulfamethizole in tissues outside the urinary tract is minimal.


Approximately 43-72% of a single oral dose of sulfamethizole may be recovered in the urine intact and as metabolites within 4 hours; approximately 84-97% of the dose is excreted within 10 hours. About 2-9% of the sulfamethizole in urine is in the N 4-acetylated form and approximately 90-95% is excreted unchanged. At pH 5, 6, 7, and 8, sulfamethizole has solubilities of about 154 mg, 724 mg, 8.25 g, and 63. g per dL, respectively. The N 4-acetylated derivative at the same pH values has solubilities of approximately 33 mg, 310 mg, 1.2 g, and 11. g per dL, respectively.

Chemistry and Stability


Sulfamethizole is a short-acting antibacterial sulfonamide. Sulfamethizole occurs as white, practically odorless crystals or powder and has a slightly bitter taste. The drug has solubilities of approximately 0.5 mg/mL in water and 26. mg/mL in alcohol at 25°C.


Sulfamethizole tablets should be stored in well-closed containers. For further information on chemistry and stability, mechanism of action, spectrum, resistance, pharmacokinetics, uses, cautions, drug interactions, and dosage and administration of sulfamethizole.


Sulfamethizole Combinations Oral Capsules 250 mg with Oxytetracycline Urobiotic®, Hydrochloride 250 mg (of Pfizer oxytetracycline) and Phenazopyridine Hydrochloride 50 mg

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