What is the use of Bactrim (Trimethoprim/Sulfamethoxazole)?

From the Guidelines

Bactrim, also known as trimethoprim-sulfamethoxazole (TMP-SMX), is an appropriate choice for therapy in women with uncomplicated bacterial cystitis, with a recommended treatment duration of 3 days, as long as local resistance rates of uropathogens do not exceed 20% 1.

Key Points to Consider

• The standard adult dose of Bactrim is typically one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) taken twice daily for 3 days in the case of uncomplicated cystitis.
• Common uses of Bactrim include urinary tract infections, but its use should be guided by local resistance patterns and the specific type of infection being treated.
• Patients should be aware of potential side effects, including rash, sun sensitivity, nausea, and rarely more serious reactions like Stevens-Johnson syndrome.
• Those with sulfa allergies should avoid Bactrim.
• Bactrim works by inhibiting two consecutive steps in bacterial folate synthesis, making it effective against many common pathogens, including Escherichia coli, which accounts for more than 75% of all bacterial cystitis.

Important Considerations for Use

• The choice of antibiotic should be based on the type of infection, local resistance patterns, and patient-specific factors such as allergy history and kidney function.
• Regular monitoring may be needed for long-term use due to potential effects on kidney function and blood counts.
• Fluoroquinolones, while highly efficacious in 3-day regimens for cystitis, have a high propensity for adverse effects and should be reserved for patients with a history of resistant organisms or specific indications where their use is justified.
• For pyelonephritis, the treatment recommendations differ, with options including oral fluoroquinolones for 7 days or TMP-SMX for 14 days, based on the IDSA/ESCMID guideline and considering the severity of the infection and patient factors.

From the FDA Drug Label

To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim oral suspension and other antibacterial drugs, sulfamethoxazole and trimethoprim oral suspension should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. Urinary Tract Infections For the treatment of urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis and Proteus vulgaris Acute Otitis Media For the treatment of acute otitis media in pediatric patients due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae Acute Exacerbations of Chronic Bronchitis in Adults For the treatment of acute exacerbations of chronic bronchitis due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae Shigellosis For the treatment of enteritis caused by susceptible strains of Shigella flexneri and Shigella sonnei Pneumocystis jirovecii Pneumonia For the treatment of documented Pneumocystis jirovecii pneumonia and for prophylaxis against P jirovecii pneumonia Traveler’s Diarrhea in Adults For the treatment of traveler’s diarrhea due to susceptible strains of enterotoxigenic E. coli.

The indications for Bactrim (trimethoprim/sulfamethoxazole) include:

• Urinary Tract Infections: due to susceptible strains of Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris
• Acute Otitis Media: in pediatric patients due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae
• Acute Exacerbations of Chronic Bronchitis: in adults due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae
• Shigellosis: due to susceptible strains of Shigella flexneri and Shigella sonnei
• Pneumocystis jirovecii Pneumonia: for treatment and prophylaxis
• Traveler’s Diarrhea: in adults due to susceptible strains of enterotoxigenic E. coli 2

From the Research

Bactrim Overview

• Bactrim, also known as trimethoprim-sulfamethoxazole, is a combination antibiotic used to treat various infections, including urinary tract infections (UTIs) 3, 4, 5, 6, 7.
• It is effective against a wide range of bacteria, but its use has been complicated by the emergence of resistance, particularly among Escherichia coli (E. coli) strains 5, 6.

Resistance Rates

• Studies have reported varying resistance rates to trimethoprim-sulfamethoxazole, ranging from 10% to over 30% 4, 5, 6, 7.
• A study published in 2016 found that E. coli strains were least resistant to fosfomycin (2.4%), while resistance rates to trimethoprim-sulfamethoxazole were significantly higher, particularly among patients over 50 years of age 5.
• Another study published in 2009 reported a resistance rate of 34% to trimethoprim-sulfamethoxazole among E. coli strains isolated from patients with uncomplicated UTIs 6.

Treatment Guidelines

• Guidelines recommend trimethoprim-sulfamethoxazole as a first-line treatment for uncomplicated UTIs, unless resistance rates in the community exceed 10% to 20% 4, 7.
• However, some studies suggest that trimethoprim-sulfamethoxazole may not be the best choice due to increasing resistance rates, and alternative antibiotics such as fosfomycin or nitrofurantoin may be more effective 4, 5.
• A study published in 2014 recommended immediate antimicrobial therapy with trimethoprim-sulfamethoxazole, nitrofurantoin, or fosfomycin for acute cystitis in adult women, while reserving fluoroquinolones for more invasive infections 4.