Active ingredient: Sulfamethoxazole - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

• Anti-Infectives
• Sulfonamides

Dosage Forms

• Tablet

Brands / Synonyms

Apo-Sulfamethoxazole; Azo Gantanol; Azo-Gantanol; Bactrim DS; Bactrimel; Co-trimoxazole; Cotrim; Cotrim D.S.; Eusaprim; Fectrim; Gamazole; Gantanol; Gantanol-DS; Metoxal; Radonil; Septra; Septran; Septrin; SIM; Simsinomin; Sinomin; Sulfamethalazole; Sulfamethoprim; Sulfamethoprim-DS; Sulfamethoxazol; Sulfamethoxizole; Sulfamethylisoxazole; Sulfatrim; Sulfisomezole; Sulmeprim; Sulmeprim Pediatric; Sulpha-Methoxizole; Sulphamethalazole; Sulphamethoxazol; Sulphamethoxazole; Sulphamethoxazole BP 98; Sulphamethylisoxazole; Sulphisomezole; Trib; Urobak; Uroplus DS; Uroplus SS

Indications

For the treatment of bronchitis, prostatitis and urinary tract infections.

Pharmacology

Sulfamethoxazole is a sulfonamide drug that inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA). Sulfamethoxazole is normally given in combination with Trimethoprim (a dihydrofolate reductase inhibitor). Studies have shown that bacterial resistance develops more slowly with the combination of the two drugs than with either Trimethoprim or Sulfamethoxazole alone.

Mechanism of Action

Sulfonamides inhibit bacterial dihydrofolate synthetase, causing interference in the conversion of p-aminobenzoic acid (PABA) into folic acid. As folic acid is a coenzyme responsible for the transport of one-carbon fragments from one molecule to another, it is an essential component of bacterial development. Pyrimethamine and trimethoprim inhibit dihydrofolate reductase, the immediate next step, and therefore act synergistically with the sulfonamides.

Absorption

Rapidly absorbed following oral administration.

Toxicity

Not Available

Biotrnasformation / Drug Metabolism

Hepatic. The metabolism of sulfamethoxazole occurs predominately by N4-acetylation, although the glucuronide conjugate has been identified.

Contraindications

Hypersensitivity to sulfonamides. Pediatric patients less than 2 months of age (except in the treatment of congenital toxoplasmosis as adjunctive therapy with pyrimethamine). Pregnancy at term and during the nursing period because sulfonamides pass the placenta and are excreted in the milk and may cause kernicterus.

Drug Interactions

In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombopenia with purpura has been reported.

It has been reported that sulfamethoxazole may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin. This interaction should be kept in mind when Gantanol is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed.

Sulfamethoxazole may inhibit the hepatic metabolism of phenytoin. At a 1.6-g dose, sulfamethoxazole produced a slight but significant increase in the half-life of phenytoin but did not produce a corresponding decrease in the metabolic clearance rate. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.

Sulfonamides can also displace methotrexate from plasma protein-binding sites, thus increasing free methotrexate concentrations.

The presence of sulfamethoxazole may interfere with the Jaffé alkaline picrate reaction assay for creatinine, resulting in overestimations of about 10% in the range of normal values.