Sulfamethoxydiazine, also known as Sulfameter, 5-Methoxysulfadiazine, and Sulphamethoxydiazine, is a synthetic sulfonamide antibacterial active pharmaceutical ingredient. It belongs to the long-acting sulfonamide group and is identified by CAS No. 651-06-9. The API has the molecular formula C₁₁H₁₂N₄O₃S and molecular weight 280.30 g/mol. NIST and PubChem identify the same chemical structure and CAS number.
Sulfamethoxydiazine is structurally related to sulfadiazine, with a methoxy substituent on the pyrimidine ring. It has historically been used as a long-acting sulfonamide antibacterial, particularly in veterinary medicine and older pharmaceutical preparations. IUPHAR/BPS lists sulfamethoxydiazine, also called sulfameter, as an approved antibacterial drug.
Sulfamethoxydiazine is chemically known as 4-amino-N-(5-methoxypyrimidin-2-yl)benzenesulfonamide. Its structure contains a sulfonamide functional group, an aniline amino group and a methoxypyrimidine ring. PubChem reports an exact molecular weight of approximately 280.063 Da, with calculated molecular weight 280.31 g/mol.
The API is distinct from Sulfamethoxydiazine Sodium, which is a separate sodium salt having CAS 18179-67-4 and formula C₁₁H₁₁N₄NaO₃S.
Sulfamethoxydiazine is generally described as a white or slightly yellow crystalline powder. Available pharmaceutical references describe it as almost insoluble in water, slightly soluble in ethanol and soluble in alkaline solutions. A historical Chinese pharmaceutical specification reports a melting range of 210–214°C.
The compound is also known by several synonyms, including Sulfameter, 5-Methoxysulfadiazine, Sulfamethoxine, Sulfametorine and Sulfametoxydiazine. NIST specifically records Sulfamethoxydiazine as a synonym of Sulfameter.
Sulfamethoxydiazine has historically been used as a long-acting sulfonamide antibacterial. Literature describes its use in the treatment and prevention of bacterial infections, particularly in veterinary applications.
Its use in modern pharmaceutical products depends on the regulatory status of the API and the applicable jurisdiction. Pharmaceutical manufacturers should evaluate the current regulatory requirements before incorporating the API into a medicinal or veterinary formulation.
Sulfamethoxydiazine acts as a structural analogue of para-aminobenzoic acid (PABA). Sulfonamide antibacterials competitively inhibit bacterial dihydropteroate synthase, disrupting folate biosynthesis. Reduced folate availability interferes with nucleotide synthesis and consequently inhibits the growth and multiplication of susceptible bacteria.
Quality control of Sulfamethoxydiazine can include identity, assay, related substances, moisture, residue on ignition or sulfated ash, residual solvents and other applicable pharmaceutical quality attributes.
A historical Chinese pharmaceutical source describes a target content of not less than 99.0% for the API and identifies 210–214°C as the melting range. However, this is not sufficient evidence for treating those figures as a current universal USP/BP/Ph. Eur. API release specification.
Therefore, numerical CMS limits for individual and total impurities should not be fabricated where a current authoritative monograph could not be verified.
Sulfamethoxydiazine API manufacturing involves controlled chemical synthesis, purification, crystallization and drying. Process controls are important for maintaining chemical identity, assay and impurity profile.
Analytical controls should cover starting-material and process-related impurities, residual solvents and other potential contaminants according to the applicable risk assessment and regulatory specification.
Sulfamethoxydiazine has a molecular formula of C₁₁H₁₂N₄O₃S and molecular weight of 280.30 g/mol. PubChem reports four rotatable bonds, seven hydrogen-bond acceptors and two hydrogen-bond donors.
The compound is reported as almost insoluble in water and soluble in alkaline solutions. Historical pharmaceutical references report a melting range of 210–214°C.
Sulfamethoxydiazine should be packaged in suitable pharmaceutical-grade, well-closed containers that protect the material from moisture, contamination and excessive environmental exposure. Historical pharmaceutical specifications indicate protection from light and storage in tightly closed containers.
A pharmaceutical API documentation package may include a Certificate of Analysis (CoA), specification sheet, Safety Data Sheet (SDS), batch analytical documentation, residual-solvent information, impurity profile and applicable regulatory documentation.
A qualified Sulfamethoxydiazine API manufacturer should maintain controlled manufacturing processes and validated analytical methods for identity, assay and related substances. Consistent raw-material controls, process monitoring, impurity management and batch traceability are important for maintaining pharmaceutical-grade API quality.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | NLT 99.0% |
| Melting Point | 210–214°C |
| Solubility | Almost insoluble in water; soluble in alkaline solution; slightly soluble in ethanol |