From the Guidelines
The dose of sulfamethoxazole (Bactrim) for treating Gram-negative infections is 1-2 double-strength tablets twice per day orally, which is equivalent to 8-12 mg/kg (based on the trimethoprim component) in either 4 divided doses intravenously or 2 divided doses orally.
Key Points
- The dosage of sulfamethoxazole is often given in combination with trimethoprim (TMP-SMX) 1.
- The recommended dose for adults is 1-2 double-strength tablets twice per day orally, with the exact dosage depending on the specific infection being treated and the patient's renal function.
- For children, the dose is 8-12 mg/kg (based on the trimethoprim component) in either 4 divided doses intravenously or 2 divided doses orally 1.
- It is essential to note that the efficacy of sulfamethoxazole for treating Gram-negative infections is poorly documented, and its use should be guided by susceptibility testing and clinical experience 1.
- The choice of antibiotic should always be based on the suspected or confirmed causative pathogen, as well as the patient's medical history, allergies, and potential drug interactions 1.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION Sulfamethoxazole and trimethoprim tablets are contraindicated in pediatric patients less than 2 months of age Urinary Tract Infections and Shigellosis in Adults and Pediatric Patients, and Acute Otitis Media in Children Adults: The usual adult dosage in the treatment of urinary tract infections is 1 sulfamethoxazole and trimethoprim DS (double strength) tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 10 to 14 days An identical daily dosage is used for 5 days in the treatment of shigellosis. Children: The recommended dose for children with urinary tract infections or acute otitis media is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days. The following table is a guideline for the attainment of this dosage: Children 2 months of age or older: Weight Dose – every 12 hours lb kg Tablets 22 10 - 44 20 1 66 30 1½ 88 40 2 or 1 DS tablet
The dose of sulfamethoxazole for treating Gram-negative infections, such as urinary tract infections and shigellosis, is:
- For adults: 1 sulfamethoxazole and trimethoprim DS (double strength) tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 10 to 14 days
- For children: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days 2
From the Research
Dose of Sulfamethoxazole for Treating Gram-Negative Infections
- The studies provided do not specify the exact dose of sulfamethoxazole (Bactrim) for treating Gram-negative infections 3, 4, 5, 6, 7.
- However, the studies suggest that sulfamethoxazole is often used in combination with trimethoprim (TMP) to treat Gram-negative infections, and the combination is effective against a variety of Gram-negative bacteria 3, 4, 5, 6.
- The minimum inhibitory concentrations (MICs) of sulfamethoxazole and trimethoprim against Gram-negative strains were determined in one study, with an MIC90 of less than 2 mg/l for most isolates 4.
- Another study found that the combination of trimethoprim and sulfamethoxazole was active in vitro against various Gram-positive and Gram-negative bacteria, and is useful for prophylaxis and treatment of selected infections of the genitourinary, respiratory, and gastrointestinal tracts 5.
- The dosage of trimethoprim-sulfamethoxazole should be adjusted when the creatinine clearance is less than 30 ml/min 5, 6.
Resistance to Sulfamethoxazole
- Increasing resistance to sulfamethoxazole has been reported, and one study analyzed the resistance genes and their relatedness to class 1 integron and insertion sequence common region in Gram-negative bacilli 7.
- The study found that the resistance mechanisms for sulfamethoxazole were different between Enterobacteriaceae and glucose non-fermenting Gram-negative bacilli, and that class 1 integron was widely disseminated in uropathogenic Gram-negative bacilli 7.