From the Guidelines
Yes, Bactrim (sulfamethoxazole/trimethoprim) is a sulfonamide antibiotic combination. Specifically, the sulfamethoxazole component is a sulfonamide drug, while trimethoprim is not a sulfonamide but rather a dihydrofolate reductase inhibitor. Together, these medications work synergistically to block two consecutive steps in bacterial folate synthesis, making Bactrim effective against many bacterial infections. This combination is commonly used to treat urinary tract infections, bronchitis, traveler's diarrhea, and Pneumocystis jirovecii pneumonia, as seen in the guidelines for preventing opportunistic infections among HIV-infected persons 1. Patients with sulfonamide allergies should avoid Bactrim, as cross-reactivity is likely. Common side effects include rash, gastrointestinal disturbances, and photosensitivity. In rare cases, more serious reactions like Stevens-Johnson syndrome or toxic epidermal necrolysis can occur. The sulfonamide component works by competing with para-aminobenzoic acid (PABA), preventing bacteria from synthesizing folic acid, which is essential for DNA production and bacterial growth.
Some key points to consider when prescribing Bactrim include:
- Resistance patterns of E. coli strains causing uncomplicated UTI vary considerably between regions and countries, as noted in the international clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women 1
- Local antimicrobial susceptibility patterns should be considered in empirical antimicrobial selection for uncomplicated UTIs
- The use of trimethoprim-sulfamethoxazole in the preceding 3–6 months is an independent risk factor for trimethoprim-sulfamethoxazole resistance in women with acute uncomplicated cystitis 1
- Travel outside the United States in the preceding 3–6 months is independently associated with trimethoprim-sulfamethoxazole resistance 1
Overall, Bactrim is a sulfonamide antibiotic combination that should be used judiciously, taking into account local resistance patterns and patient-specific factors.
From the FDA Drug Label
As with all drugs containing sulfonamides, caution is advisable in patients with porphyria or thyroid dysfunction.
- Bactrim contains a sulfonamide: The FDA drug label for Bactrim 2 indicates that it contains a sulfonamide, specifically sulfamethoxazole.
- Sulfamethoxazole is a sulfonamide: The FDA drug label for sulfamethoxazole 3 and 3 also confirms that sulfamethoxazole is a sulfonamide. Bactrim (sulfamethoxazole/trimethoprim) is a sulfonamide.
From the Research
Bactrim Composition
Sulfonamide Classification
- Sulfamethoxazole, a component of Bactrim, is a sulfonamide antibiotic 8.
- Sulfonamides are a class of antimicrobials that exhibit antibacterial properties 8.
Bactrim as a Sulfonamide
- Given that sulfamethoxazole is a sulfonamide, Bactrim (sulfamethoxazole/trimethoprim) can be classified as a sulfonamide-containing antibiotic 4, 8.