What are the dosages and indications for Trimethoprim-Sulfamethoxazole (Bactrim)?

From the Guidelines

Bactrim (sulfamethoxazole-trimethoprim) is typically dosed based on the trimethoprim component, with standard adult dosing for urinary tract infections being 160mg trimethoprim/800mg sulfamethoxazole (one double-strength tablet) twice daily for 3-14 days depending on infection severity. For skin infections, the same dosage is used for 7-14 days. For Pneumocystis pneumonia treatment, higher doses of 15-20mg/kg/day of trimethoprim component divided into 3-4 doses for 14-21 days are recommended 1. For PCP prophylaxis, one double-strength tablet daily or three times weekly is standard. Pediatric dosing is calculated at 8-12mg/kg/day of trimethoprim divided into two doses. Bactrim works by inhibiting two sequential steps in bacterial folate synthesis, making it effective against many gram-positive and gram-negative bacteria. Common side effects include rash, gastrointestinal upset, and photosensitivity. Bactrim should be used cautiously in patients with renal impairment, and dose adjustments are necessary for creatinine clearance below 30 mL/min. It's contraindicated in patients with sulfa allergies, pregnant women near term, nursing mothers, and infants under 2 months old.

Some key points to consider when prescribing Bactrim include:

• The need for dose adjustments in patients with renal impairment 1
• The potential for adverse effects such as rash, gastrointestinal upset, and photosensitivity 1
• The importance of using Bactrim in combination with other antibiotics in certain cases, such as in the treatment of skin and soft tissue infections caused by MRSA 1
• The need to monitor patients for signs of resistance or treatment failure, particularly in cases where Bactrim is used as monotherapy 1

In terms of specific dosing recommendations, the following guidelines can be followed:

• For urinary tract infections, use 160mg trimethoprim/800mg sulfamethoxazole (one double-strength tablet) twice daily for 3-14 days depending on infection severity 1
• For skin infections, use the same dosage as for urinary tract infections, for 7-14 days 1
• For Pneumocystis pneumonia treatment, use higher doses of 15-20mg/kg/day of trimethoprim component divided into 3-4 doses for 14-21 days 1
• For PCP prophylaxis, use one double-strength tablet daily or three times weekly 1

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Not recommended for use 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 tablet (double strength) or 2 sulfamethoxazole and trimethoprim tablets (400 mg/80 mg) 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. An identical daily dosage is used for 5 days in the treatment of shigellosis The following table is a guideline for the attainment of this dosage: Children 2 months of age or older: WeightDose-every 12 hours lbkgTablets 2210- 44201 66301½ 88402 (400 mg/80 mg) or 1 (DS) tablet For Patients with Impaired Renal Function: When renal function is impaired, a reduced dosage should be employed using the following table: Creatinine Clearance (mL/min)Recommended Dosage Regimen Above 30Usual standard regimen 15-30½ the usual regimen Below 15Use not recommended Acute Exacerbations of Chronic Bronchitis in Adults: The usual adult dosage in the treatment of acute exacerbations of chronic bronchitis is 1 sulfamethoxazole and trimethoprim tablet (double strength) or 2 sulfamethoxazole and trimethoprim tablets (400 mg/80 mg) every 12 hours for 14 days Pneumocystis Carinii Pneumonia: Treatment: Adults and Children The recommended dosage for treatment of patients with documented Pneumocystis carinii pneumonia is 75 to 100 mg/kg sulfamethoxazole and 15 to 20 mg/kg trimethoprim per 24 hours given in equally divided doses every 6 hours for 14 to 21 days. The following table is a guideline for the upper limit of this dosage WeightDose-every 6 hours lbkgTablets 188- 35161 53241½ 70322 (400 mg/80 mg) or 1 (DS) tablet 88402½ 106483 (400 mg/80 mg) or 1½ (DS) tablets 141644 (400 mg/80 mg) or 2 (DS) tablets 176805 (400 mg/80 mg) or 2½ (DS) tablets For the lower limit dose (75 mg/kg sulfamethoxazole and 15 mg/kg trimethoprim per 24 hours) administer 75% of the dose in the above table Prophylaxis: Adults: The recommended dosage for prophylaxis in adults is 1 sulfamethoxazole and trimethoprim tablet (double strength) daily. Children: For children, the recommended dose is 750 mg/m2/day sulfamethoxazole with 150 mg/m2/day trimethoprim given orally in equally divided doses twice a day, on 3 consecutive days per week. The total daily dose should not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim. The following table is a guideline for the attainment of this dosage in children: Body Surface AreaDose-every 12 hours (m2)Tablets 0.26- 0.53½ 1.061 Traveler's Diarrhea in Adults: For the treatment of traveler's diarrhea, the usual adult dosage is 1 sulfamethoxazole and trimethoprim tablet (double strength) or 2 sulfamethoxazole and trimethoprim tablets (400 mg/80 mg) every 12 hours for 5 days.

The indications for Bactrim are:

• Urinary Tract Infections
• Shigellosis
• Acute Otitis Media
• Acute Exacerbations of Chronic Bronchitis
• Pneumocystis Carinii Pneumonia
• Traveler's Diarrhea The dosages for Bactrim are:
• Adults: 1 sulfamethoxazole and trimethoprim tablet (double strength) or 2 sulfamethoxazole and trimethoprim tablets (400 mg/80 mg) every 12 hours for 10 to 14 days for urinary tract infections and shigellosis
• Children: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days for urinary tract infections and acute otitis media
• For Pneumocystis Carinii Pneumonia: 75 to 100 mg/kg sulfamethoxazole and 15 to 20 mg/kg trimethoprim per 24 hours given in equally divided doses every 6 hours for 14 to 21 days 2

From the Research

Bactrim Dosages and Indications

Bactrim, also known as trimethoprim-sulfamethoxazole, is a synthetic anti-infective preparation that acts synergistically to inhibit the growth of certain microorganisms 3. The combination is effective orally in acute and chronic urinary tract infections, as well as other infectious conditions such as:

• Bacterial upper respiratory tract infections
• Ear infections
• Skin and soft-tissue infections
• Septicemias
• Acute and subacute bacterial endocarditis
• Enteric fever
• Brucellosis
• Prostatitis
• Gonorrhea

Usage and Resistance

The antimicrobial combination of trimethoprim and sulfamethoxazole is active in vitro against a variety of gram-positive and gram-negative bacteria 4. However, resistance to trimethoprim-sulfamethoxazole has been reported, particularly in the treatment of uncomplicated urinary tract infections 5, 6. Studies have shown that:

• Resistance to trimethoprim-sulfamethoxazole is common in Escherichia coli isolates from patients with uncomplicated urinary tract infections
• Prior urinary infection/colonisation with trimethoprim-sulfamethoxazole-resistant Enterobacteriaceae and recent use of trimethoprim-sulfamethoxazole are predictors of resistance
• Fosfomycin may be a viable alternative for the treatment of uncomplicated urinary tract infections, particularly in patients with risk factors for trimethoprim-sulfamethoxazole resistance

Dosage Adjustments

The dosage of trimethoprim-sulfamethoxazole should be adjusted in patients with decreased renal function, particularly when the creatinine clearance is less than 30 ml/min 4. This is because the native compounds and metabolites of trimethoprim and sulfamethoxazole are excreted primarily in the urine.