What is Bactrim DS (sulfamethoxazole/trimethoprim) used for?

Bactrim DS 800/160: Clinical Indications

Bactrim DS (sulfamethoxazole 800 mg/trimethoprim 160 mg) is FDA-approved and guideline-recommended for treating urinary tract infections, acute otitis media, acute exacerbations of chronic bronchitis, shigellosis, Pneumocystis jiroveci pneumonia, and traveler's diarrhea. 1

FDA-Approved Indications

Urinary Tract Infections

• For acute uncomplicated cystitis in women: Bactrim DS 800/160 mg twice daily for 3 days achieves 90-100% clinical cure rates when the organism is susceptible. 2, 3
• Should only be used empirically when local E. coli resistance rates are <20%. 2, 3
• Effective against susceptible strains of E. coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris. 1
• When the uropathogen is susceptible, cure rate is 84%; when resistant, cure rate drops to only 41%. 2
• The 3-day regimen is optimal for uncomplicated cystitis with early bacteriologic cure rates of 91%. 2

Respiratory Infections

• Approved for acute exacerbations of chronic bronchitis caused by susceptible Streptococcus pneumoniae or Haemophilus influenzae. 1, 4
• Approved for acute otitis media in pediatric patients (≥2 months old) due to susceptible S. pneumoniae or H. influenzae. 1
• Not indicated for prophylactic or prolonged administration in otitis media at any age. 1

Gastrointestinal Infections

• Treatment of shigellosis caused by susceptible Shigella flexneri and Shigella sonnei. 1
• For confirmed Shigella infections, alternatives like ceftriaxone may be more effective than fluoroquinolones. 5
• Treatment of traveler's diarrhea due to susceptible enterotoxigenic E. coli. 1
• For non-typhi Salmonella species: antibiotics not routinely recommended, but Bactrim DS can be used if susceptible for severe infection or high-risk patients (<6 months, >50 years, or with prostheses, valvular heart disease, severe atherosclerosis, malignancy, or uremia). 5

Pneumocystis jiroveci Pneumonia

• Treatment of documented P. jiroveci pneumonia. 1, 6, 7
• Prophylaxis against P. jiroveci pneumonia in immunosuppressed individuals at increased risk. 1
• The dose for Pneumocystis prophylaxis is generally well-tolerated but requires monitoring when used with methotrexate due to potential drug interactions at the 800/160 mg twice daily dosing. 5

Off-Label Uses

Skin and Soft Tissue Infections

• Used for MRSA skin abscesses when susceptible, particularly for localized infections after incision and drainage. 5
• Should not be used as a single agent for initial treatment of cellulitis due to possible group A Streptococcus involvement and intrinsic resistance. 5
• Off-label use for acne vulgaris and other skin infections, especially MRSA. 8

Other Infections

• Effective for Nocardia asteroides infections, either alone or in combination with other antimicrobials. 6, 7
• Used for prostatitis and acute pyelonephritis. 4
• May be used for prophylaxis against recurrent bacterial respiratory infections in HIV-infected patients, though caution is warranted due to potential development of drug-resistant organisms. 5

Critical Prescribing Considerations

Resistance Patterns

• Local resistance surveillance is essential before empiric use—do not use if local resistance exceeds 20%. 2, 3, 9
• Indiscriminate use fosters resistance emergence, negating the value of both trimethoprim and trimethoprim-sulfamethoxazole. 10

Dosing Adjustments

• When creatinine clearance is <30 mL/min, dosage adjustment is required. 6, 7
• The native compounds and metabolites are excreted primarily in urine. 6, 7

Safety Concerns

• Relatively nontoxic in patients without AIDS. 6
• Most common adverse reactions: gastrointestinal intolerance and skin eruptions. 10
• Severe hypersensitivity reactions can occur, particularly when added to other therapies. 5
• Safety in pregnancy has not been established. 10
• Limited data on safety of repeated use in pediatric patients under 2 years of age. 1

Drug Interactions

• Potential interaction with methotrexate when dosed at 800/160 mg twice daily; the lower prophylactic dose is generally tolerated but requires monitoring. 5