When is Bactrim (trimethoprim/sulfamethoxazole) indicated for use?

When to Use Bactrim (Trimethoprim-Sulfamethoxazole)

FDA-Approved Indications

Bactrim should be used for specific proven or strongly suspected bacterial infections caused by susceptible organisms, not as a broad-spectrum first-line agent. 1

Primary Indications

• Urinary tract infections caused by susceptible E. coli, Klebsiella, Enterobacter, Morganella morganii, Proteus mirabilis, and Proteus vulgaris 1

  • For uncomplicated UTIs, single-agent therapy is preferred over combination agents initially 1
  • TMP-SMX 160/800 mg twice daily for 14 days is appropriate for pyelonephritis when the pathogen is known to be susceptible 2
  • Effective for both acute and chronic urinary tract infections 3, 4

• Acute otitis media in pediatric patients (≥2 years old) due to susceptible Streptococcus pneumoniae or Haemophilus influenzae, only when it offers advantage over other agents 1

  • Not indicated for prophylaxis or prolonged use in otitis media 1
  • Limited safety data for repeated use in children under 2 years 1

• Acute exacerbations of chronic bronchitis in adults due to susceptible S. pneumoniae or H. influenzae 1

  • Important caveat: Routine antibiotic treatment of uncomplicated acute bronchitis is NOT recommended regardless of cough duration 5

• Shigellosis caused by susceptible Shigella flexneri and Shigella sonnei when antibacterial therapy is indicated 1

• Pneumocystis jiroveci pneumonia for both treatment and prophylaxis in immunosuppressed individuals at increased risk 1

• Traveler's diarrhea in adults due to susceptible enterotoxigenic E. coli 1

Specialized Uses

Surgical Prophylaxis

• Single oral dose of TMP-SMX for urodynamic studies in high-risk patients: those with neurogenic bladder, immunosuppression, recent GU instrumentation, or recent antimicrobial use 5
• Alternatives include first- or second-generation cephalosporins, amoxicillin/clavulanate, or aminoglycoside-ampicillin 5

Skin and Soft Tissue Infections

• MRSA coverage: TMP-SMX is an alternative for skin abscesses when MRSA is suspected or confirmed, particularly in penicillin-allergic patients 5
• Critical limitation: Should NOT be used as single agent for initial cellulitis treatment due to intrinsic resistance of Group A Streptococcus 5

Parasitic Infections

• Effective prophylaxis against Paracoccidioides brasiliensis when used as primary prophylaxis for Pneumocystis jiroveci pneumonia in endemic areas 5

Perioperative Prophylaxis in MDR Colonization

• Consider IV TMP-SMX as alternative for patients colonized with extended-spectrum cephalosporin-resistant Enterobacterales before surgery, if susceptibility is confirmed 5

Key Prescribing Principles

When to Obtain Cultures

• Always obtain urine culture and susceptibility testing before initiating therapy for pyelonephritis 2
• Culture and susceptibility information should guide therapy selection when available 1

Resistance Considerations

• Use only when local resistance patterns support its use 5
• For pyelonephritis, fluoroquinolones are preferred in areas where resistance is <10%; if using TMP-SMX, confirm susceptibility first 2
• Serial surveys suggest increasing trimethoprim resistance among enterobacteria, though emergence during therapy has been infrequent 3

Dosing Duration

• Uncomplicated UTI: Standard course (typically 3-5 days for cystitis) 3
• Pyelonephritis: 14 days when pathogen is susceptible 2
• Prophylaxis for recurrent UTI: 100mg trimethoprim daily as single nighttime dose 3
• Acute otitis media/bronchitis: Per standard protocols 1

Common Pitfalls to Avoid

• Never use for uncomplicated acute bronchitis - this is explicitly not recommended regardless of cough duration or purulent sputum 5
• Never use as monotherapy for cellulitis due to Group A Streptococcus resistance 5
• Do not use in pregnant women - safety has not been established 6
• Avoid indiscriminate use as this fosters resistance and negates value of both TMP-SMX and trimethoprim alone 6
• Do not use for prophylaxis in otitis media at any age 1
• Monitor for hematologic toxicity and nephrotoxicity, especially with long-term use 7

Adverse Effects Profile

• Gastrointestinal intolerance and skin eruptions are most common 6
• Generally better tolerated than co-trimoxazole with fewer skin rashes and GI upset when trimethoprim used alone 3
• Risk of Stevens-Johnson syndrome exists, making it less desirable when alternatives exist 5