Last reviewed 2026-04-22 · How we verify

Sulfamethoxazole / Trimethoprim Injectable Product

Sulfamethoxazole and trimethoprim are synergistic antibiotics that inhibit bacterial folate synthesis by blocking dihydropteroate synthase and dihydrofolate reductase, respectively.

Sulfamethoxazole and trimethoprim are synergistic antibiotics that inhibit bacterial folate synthesis by blocking dihydropteroate synthase and dihydrofolate reductase, respectively. Used for Urinary tract infections, Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment, Bacterial infections (gram-positive and gram-negative).

At a glance

Mechanism of action

Sulfamethoxazole is a sulfonamide that inhibits dihydropteroate synthase, preventing the condensation of para-aminobenzoic acid (PABA) with pteridine to form dihydropteroate. Trimethoprim inhibits dihydrofolate reductase, blocking the conversion of dihydrofolate to tetrahydrofolate. Together, they create a sequential blockade of the bacterial folate synthesis pathway, resulting in bactericidal activity against a broad spectrum of gram-positive and gram-negative organisms.

Approved indications

• Urinary tract infections
• Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
• Bacterial infections (gram-positive and gram-negative)
• Toxoplasmosis

Common side effects

• Rash
• Nausea
• Vomiting
• Hyperkalemia
• Stevens-Johnson syndrome
• Hepatotoxicity
• Bone marrow suppression

Key clinical trials

• Testing a Novel Combination Treatment (Arm D) Versus Standard of Care for Intensive Phase Treatment for Mycobacterium Abscessus Pulmonary Disease in People With or Without Cystic Fibrosis in the Finding the Optimal Regimen for Mycobacterium Abscessus Treatment (FORMaT) Adaptive Platform Trial (PHASE2)
• Oral Antimicrobial Treatment vs. Outpatient Parenteral for Infective Endocarditis (PHASE4)
• Study of Rezafungin Compared to Standard Antimicrobial Regimen for Prevention of Invasive Fungal Diseases in Adults Undergoing Allogeneic Blood and Marrow Transplantation (PHASE3)
• [18F]Fluoropropyl-Trimethoprim ([18F]F-TMP) PET/CT Imaging to Evaluate Biodistribution and Kinetics in Human Subjects (PHASE1)
• 11C-Trimethoprim PET/CT Imaging to Evaluate Biodistribution and Kinetics in Human Subjects (PHASE1)
• A Study of the Safety and Tolerability of ASP7317 in Senior Adults Who Are Losing Their Clear, Sharp Central Vision Due to Geographic Atrophy Secondary to Dry Age-related Macular Degeneration (PHASE1)
• Bacteriophage Therapy for Mycobacterium Abscessus Pulmonary Infection (PHASE1)
• Early Vedolizumab as First-Line for Immune-Related Colitis Therapy Trial (PHASE2)

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.