Sulfamethoxazole + Trimethoprim is a synthetic antibacterial combination consisting of the sulfonamide antibacterial Sulfamethoxazole and the dihydrofolate-reductase inhibitor Trimethoprim. The combination is widely known as a synergistic antibacterial therapy because the two active ingredients inhibit sequential steps in the bacterial folate pathway.
Sulfamethoxazole is chemically identified as N¹-(5-methyl-3-isoxazolyl)sulfanilamide, with molecular formula C₁₀H₁₁N₃O₃S and molecular weight 253.28 g/mol. Trimethoprim is 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine, with molecular formula C₁₄H₁₈N₄O₃ and molecular weight 290.32 g/mol.
The combination is available in pharmaceutical dosage forms including conventional tablets and double-strength tablets. A commonly marketed strength contains 400 mg sulfamethoxazole + 80 mg trimethoprim, while the double-strength formulation contains 800 mg sulfamethoxazole + 160 mg trimethoprim.
Sulfamethoxazole and Trimethoprim are chemically distinct antibacterial substances that act at different stages of bacterial folate metabolism.
Sulfamethoxazole is a sulfonamide compound and structural analogue of para-aminobenzoic acid. It inhibits bacterial dihydropteroate synthase, thereby interfering with the formation of dihydrofolate.
Trimethoprim inhibits bacterial dihydrofolate reductase, blocking the conversion of dihydrofolate to tetrahydrofolate.
The sequential inhibition of folate metabolism produces enhanced antibacterial activity when the two components are administered together.
Sulfamethoxazole + Trimethoprim is used for the treatment and prevention of susceptible bacterial infections when the combination is clinically appropriate.
FDA labeling identifies the combination as an antibacterial product and states that it should be used only for infections that are proven or strongly suspected to be caused by susceptible bacteria.
Depending on the approved formulation and indication, Sulfamethoxazole + Trimethoprim products are used in the management of susceptible infections involving the urinary tract, respiratory tract and other susceptible bacterial infections. The combination is also used in specific clinical settings for prevention or treatment of Pneumocystis jirovecii pneumonia (PJP/PCP) under appropriate medical supervision.
The precise indication, dosage, strength and regulatory status depend on the finished pharmaceutical product and applicable market authorization.
The antibacterial activity of Sulfamethoxazole + Trimethoprim results from sequential inhibition of bacterial folate synthesis.
Sulfamethoxazole competes with PABA and inhibits dihydropteroate synthase, reducing formation of dihydrofolate precursors.
Trimethoprim subsequently inhibits dihydrofolate reductase, reducing the conversion of dihydrofolate to tetrahydrofolate.
Blocking these consecutive enzymatic steps disrupts bacterial folate metabolism and interferes with synthesis of nucleic acids and other essential cellular components. This produces the characteristic synergistic antibacterial effect of the combination.
USP provides a monograph for Sulfamethoxazole and Trimethoprim Tablets. The USP definition specifies that the tablets contain NLT 93.0% and NMT 107.0% of the labeled amounts of both sulfamethoxazole and trimethoprim.
The USP assay for the combination uses liquid chromatography to separately quantify sulfamethoxazole and trimethoprim. USP reference standards include Sulfamethoxazole RS and Trimethoprim RS.
The individual active ingredients also have their own pharmacopoeial specifications. USP specifies 98.5–101.0% for Trimethoprim on the dried basis.
For Sulfamethoxazole, the USP monograph specifies loss on drying NMT 0.5% and residue on ignition NMT 0.1%, among other requirements.
Swapnroop Drugs and Pharmaceuticals provides pharmaceutical API manufacturing and quality-support capabilities for Sulfamethoxazole and Trimethoprim, with analytical evaluation according to applicable pharmacopoeial and customer-specific requirements.
For combination-product manufacturers, the individual APIs can be evaluated separately for identity, assay, related substances and other applicable quality parameters before formulation into the required Sulfamethoxazole + Trimethoprim dosage form.
For customers seeking Sulfamethoxazole + Trimethoprim pharmaceutical APIs from India, product specifications, analytical documentation and commercial requirements can be evaluated according to the intended formulation and applicable regulatory market.
Sulfamethoxazole and Trimethoprim APIs should be stored in suitable well-closed, protective pharmaceutical-grade packaging according to the applicable individual API specification and stability requirements.
The finished Sulfamethoxazole + Trimethoprim dosage form should be stored according to its approved product labeling and stability data.
Appropriate packaging should protect the APIs or finished product from moisture, contamination, excessive heat and other environmental factors that could adversely affect quality.
Depending on customer and regulatory requirements, documentation may include:
Sulfamethoxazole + Trimethoprim is an established antibacterial combination based on complementary inhibition of the bacterial folate pathway. USP provides specific quality requirements for the finished tablet combination, including 93.0–107.0% of the labeled amount for each active ingredient.
Swapnroop Drugs and Pharmaceuticals focuses on controlled pharmaceutical API manufacturing, analytical quality evaluation and documentation support for customers requiring Sulfamethoxazole and Trimethoprim for pharmaceutical manufacturing.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 93.0–107.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.1% |