Sulfinpyrazone is a synthetic uricosuric active pharmaceutical ingredient (API) used to reduce serum uric acid levels. It belongs to the pyrazolidinedione class and is structurally related to phenylbutazone. The API is identified by CAS No. 57-96-5, molecular formula C₂₃H₂₀N₂O₃S, and molecular weight 404.48 g/mol. The current BP 2025/Ph. Eur. monograph identifies Sulfinpyrazone as a uricosuric substance and specifies a content of 99.0%–101.0% on a dried-substance basis.
Sulfinpyrazone is also known internationally as Sulphinpyrazone, with historical brand names including Anturane and Anturan. FDA GSRS assigns the substance UNII V6OFU47K3W.
Sulfinpyrazone acts primarily as a uricosuric agent. It increases renal excretion of uric acid by reducing its tubular reabsorption, thereby helping lower serum urate concentrations. PubChem classifies it as a uricosuric drug used in gout therapy.
The API is supplied as a white or almost white powder. The BP/Ph. Eur. monograph describes it as very slightly soluble in water, sparingly soluble in ethanol (96%), and soluble in dilute solutions of alkali hydroxides.
The pharmacopoeial chemical name of Sulfinpyrazone is 1,2-diphenyl-4-[2-(phenylsulfinyl)ethyl]pyrazolidine-3,5-dione. The molecule contains a sulfoxide functional group and a pyrazolidine-3,5-dione ring system.
PubChem reports an exact mass of 404.11946368 Da, XLogP3 of approximately 2.3, four hydrogen-bond acceptors and six rotatable bonds. The substance has one undefined atom stereocenter, so stereochemical considerations should be appropriately controlled where relevant to the material specification.
Sulfinpyrazone has been used as a uricosuric medicine in gout therapy. Rather than directly reducing inflammation, its principal pharmacological role is to increase urinary elimination of uric acid and reduce serum urate concentrations.
Historical pharmacological literature also describes antiplatelet activity associated with Sulfinpyrazone and its metabolites. However, its principal pharmacological classification is uricosuric.
Sulfinpyrazone promotes uric acid excretion through its effects on renal tubular urate transport. By inhibiting renal tubular reabsorption of urate, it increases urinary uric acid elimination and lowers circulating serum urate levels.
Sulfinpyrazone has a current BP 2025 / Ph. Eur. monograph 0790, which provides specific numerical quality requirements. The content requirement is 99.0%–101.0% on a dried-substance basis.
The monograph controls related substances by liquid chromatography. Impurities A and B are each limited to NMT 1.0%, impurity C is limited to NMT 0.2%, each unspecified impurity is limited to NMT 0.10%, and total impurities are limited to NMT 2.0%. The disregard limit is 0.05%.
Loss on drying is controlled at NMT 0.5%, while sulfated ash is controlled at NMT 0.1%.
Sulfinpyrazone API manufacturing involves controlled chemical synthesis, purification, crystallization and drying. Manufacturing controls should ensure consistent chemical identity, assay, impurity profile, moisture content and solid-state characteristics.
Particular attention is required for related substances because the current Ph. Eur. monograph specifically identifies sulfinpyrazone impurities A, B and C.
Sulfinpyrazone occurs as a white or almost white powder. The BP/Ph. Eur. identification procedure specifies a melting-point range of 131–135°C.
The API is very slightly soluble in water and sparingly soluble in ethanol (96%). It dissolves in dilute alkali hydroxide solutions.
Independent experimental research has also characterized Sulfinpyrazone solubility in water and a range of organic solvents, confirming that solubility is strongly dependent on solvent and temperature.
The BP/Ph. Eur. monograph specifies that Sulfinpyrazone should be protected from light. Pharmaceutical-grade packaging should also protect the API from moisture and contamination.
Typical API documentation can include a Certificate of Analysis (CoA), specification sheet, Safety Data Sheet (SDS), analytical test reports, impurity profile, batch documentation, stability information and applicable regulatory documentation.
A qualified Sulfinpyrazone API manufacturer should maintain validated manufacturing and analytical processes capable of consistently meeting the applicable pharmacopoeial requirements. Key quality attributes include assay, related substances, loss on drying, sulfated ash, identity and physical characteristics.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 99.0–101.0% |
| Loss on Drying | NMT 0.5% |
| Individual Impurity | NMT 0.10% |
| Total Impurities | NMT 2.0% |
| Melting Point | 131–135°C |