From the FDA Drug Label
Sulfamethoxazole and trimethoprim is a synthetic antibacterial combination product Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA). Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the required enzyme, dihydrofolate reductase
Bactrim DS is a type of antibiotic known as a sulfonamide, specifically a combination of sulfamethoxazole and trimethoprim. It works by inhibiting the growth of bacteria by blocking two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria 1.
- Key components:
- Sulfamethoxazole: inhibits bacterial synthesis of dihydrofolic acid
- Trimethoprim: blocks the production of tetrahydrofolic acid from dihydrofolic acid
- Mechanism of action: blocks two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria 2 1
From the Research
Bactrim DS is a combination antibiotic that belongs to the class of medications called folate antagonists or antifolates, containing sulfamethoxazole and trimethoprim. This antibiotic works by inhibiting two consecutive steps in the bacterial folate synthesis pathway, which is essential for bacterial DNA production and cell reproduction. Specifically, sulfamethoxazole blocks the incorporation of para-aminobenzoic acid (PABA) into folic acid, while trimethoprim inhibits the enzyme dihydrofolate reductase. This dual mechanism creates a synergistic effect that makes Bactrim effective against many gram-positive and gram-negative bacteria, as noted in a study published in the Journal of the American Medical Association 3. Bactrim is commonly used to treat urinary tract infections, respiratory infections like pneumocystis pneumonia, ear infections, traveler's diarrhea, and certain types of MRSA skin infections. The standard adult dose is typically one double-strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours, though dosing varies by condition, and patients should stay well-hydrated while using this medication to prevent kidney complications, as recommended in the Mayo Clinic proceedings 4. Some key points to consider when prescribing Bactrim include:
- The medication is relatively nontoxic and available in oral and intravenous forms 4
- The native compounds and the metabolites of trimethoprim and sulfamethoxazole are excreted primarily in the urine, and dosage adjustments may be necessary in patients with decreased creatinine clearance 4
- Trimethoprim-sulfamethoxazole is the antimicrobial agent of choice for Pneumocystis carinii pneumonia 4
- Patients should take the full course as prescribed, even if symptoms improve, to ensure complete eradication of the infection.