What is the dosage and usage of Co-trimoxazole (trimethoprim/sulfamethoxazole) for treating bacterial infections?

From the Guidelines

Co-trimoxazole (trimethoprim/sulfamethoxazole) is typically dosed based on the trimethoprim component, with a standard dose of one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) taken orally every 12 hours for 7-14 days, depending on the infection type, as recommended by the Infectious Diseases Society of America 1. For most common bacterial infections in adults, this dosing is applicable.

• For urinary tract infections, a shorter course of 3 days may be sufficient, as seen in studies comparing trimethoprim-sulfamethoxazole with other antibiotics for acute uncomplicated cystitis 1.
• Children's dosing is weight-based, usually 8 mg/kg/day of trimethoprim divided into two doses.
• For Pneumocystis pneumonia treatment, higher doses are required: 15-20 mg/kg/day of trimethoprim component divided into 3-4 doses for 14-21 days. The medication should be taken with plenty of fluids to prevent crystal formation in the urine. Co-trimoxazole works by blocking two consecutive steps in bacterial folate synthesis, making it bactericidal. Common side effects include rash, gastrointestinal disturbances, and rarely, severe skin reactions or blood disorders. The medication should be avoided in patients with sulfa allergies, and dose adjustments are necessary for those with kidney impairment, as indicated in guidelines for the diagnosis and management of skin and soft tissue infections 1. It's also important to consider the rising rates of trimethoprim-sulfamethoxazole resistance among uropathogens, especially outside of the United States, as noted in international clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women 1.

From the FDA Drug Label

DOSAGE & ADMINISTRATION Sulfamethoxazole and trimethoprim is 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 four teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension 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: Weight Dose - every 12 hours lb kg Teaspoonfuls 22 10 1 (5 mL) 44 20 2 (10 mL) 66 30 3 (15 mL) 88 40 4 (20 mL) 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 30 Usual standard regimen 15–30 ½ the usual regimen Below 15 Use not recommended Acute Exacerbations of Chronic Bronchitis in Adults: The usual adult dosage in the treatment of acute exacerbations of chronic bronchitis is four teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension every 12 hours for 14 days Pneumocystis jirovecii Pneumonia: Treatment: Adults and Children: The recommended dosage for treatment of patients with documented Pneumocystis jirovecii 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: Weight Dose - every 6 hours lb kg Teaspoonfuls 18 8 1 (5 mL) 35 16 2 (10 mL) 53 24 3 (15 mL) 70 32 4 (20 mL) 88 40 5 (25 mL) 108 48 6 (30 mL) 141 64 8 (40 mL) 176 80 10 (50 mL) 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 four teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension 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 Area Dose – every 12 hours (m2) Teaspoonfuls 0.26 ½ (2.5 mL) 0.53 1 (5 mL) 1.06 2 (10 mL) Traveler's Diarrhea in Adults: For the treatment of traveler's diarrhea, the usual adult dosage is four teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension every 12 hours for 5 days.

The dosage and usage of Co-trimoxazole (trimethoprim/sulfamethoxazole) for treating bacterial infections are as follows:

• Urinary Tract Infections and Shigellosis:
  • Adults: 4 teaspoonfuls (20 mL) every 12 hours for 10 to 14 days
  • Children: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days
• Acute Exacerbations of Chronic Bronchitis in Adults: 4 teaspoonfuls (20 mL) every 12 hours for 14 days
• Pneumocystis jirovecii Pneumonia:
  • Treatment: 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
  • Prophylaxis:
    • Adults: 4 teaspoonfuls (20 mL) daily
    • Children: 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
• Traveler's Diarrhea in Adults: 4 teaspoonfuls (20 mL) every 12 hours for 5 days
• Impaired Renal Function: reduced dosage should be employed based on creatinine clearance 2

From the Research

Dosage and Usage of Co-trimoxazole

• The dosage of Co-trimoxazole for treating bacterial infections can vary depending on the type and severity of the infection.
• A study published in 1980 3 found that a single dose of at least 1.92 g (four tablets Septrin or Bactrim) was effective in treating uncomplicated urinary tract infections.
• Another study from 1980 4 compared the effectiveness of single-day treatment (two tablets of 0.96 grams twice a day) and single-dose treatment (four tablets of 1.92 grams) with a seven-day course of Co-trimoxazole, and found that the infection cure rate was comparable in each group.
• However, the study also found that patients who received the single dose had a high incidence of minor side effects, suggesting that one-day treatment may be the preferred mode of treatment.

Indications for Co-trimoxazole Use

• Co-trimoxazole is effective against a wide range of bacterial, fungal, and protozoal pathogens, including Nocardia, Listeria monocytogenes, Brucella, and Pneumocystis jirovecii 5.
• It is also used to treat toxoplasmosis, brucellosis, nocardiosis, chancroid, and pneumonia caused by Pneumocystis carinii 6.
• However, for many common infections, trimethoprim alone may be preferable to Co-trimoxazole due to its lower risk of adverse events and equivalent effectiveness 6, 7.

Restrictions on Co-trimoxazole Use

• In 1995, the licensed indications for Co-trimoxazole were narrowed to reflect the recommendation that it should only be used for specific infections where its use is justified 7.
• The use of Co-trimoxazole is now restricted to certain cases, and prescribers are advised to be alert to the possibility of unwanted effects and to use the drug only when necessary.