Sulphadimidine Sodium Pharma Grade API is the sodium salt of sulphadimidine (sulfamethazine), produced as a compendial-grade active pharmaceutical ingredient for tablet, capsule, granule, injection, oral liquid, and other aqueous injectable or oral presentations. The molecule is identified by CAS 1981-58-4, empirical formula C12H13N4NaO2S, and molar mass 300.32 g/mol. The sodium counterion changes the solubility and processing profile substantially: sulphadimidine base is practically insoluble in water, whereas the sodium salt dissolves freely and yields an alkaline solution. Pharmaceutical grades are controlled for identity, assay, related substances, residual solvents, elemental impurities, loss on drying, and, where requested, bacterial endotoxins and particle-size distribution. In commerce the API is offered as a standard-milled powder, a micronised variant for higher surface-area dissolution, and a low-endotoxin injectable grade for parenteral manufacture. Each variant is packed in sealed moisture-proof packaging with desiccant and should be stored below 25°C in an environment below 60% RH. Material that is exposed to humid air softens and cakes; before use, any bag opened in uncontrolled conditions should be re-screened and its moisture content rechecked.

How Does the Sodium Salt Form Affect Formulation Behaviour Across Tablet, Capsule, Granule, and Injectable Processes?

Because the sodium salt ionises in aqueous media, it dissolves rapidly in the small volume of surface water present during wet granulation. This behaviour reduces the need for surfactant wetting agents that are commonly required with sulphadimidine base, but it introduces a different set of process controls. In tablet and capsule manufacture, the API can be processed by direct compression, dry granulation, or aqueous wet granulation. Direct compression is feasible only when the starting particle size and bulk density are controlled; a typical oral-solid grade has a d(0.9) not exceeding 100 µm and a loose bulk density in the range 0.35–0.55 g/mL. If the as-received powder is coarse or shows angle of repose above 40° per USP <1174>, dry granulation or wet granulation is preferred.

Wet granulation with the sodium salt requires lower granulating-liquid addition than a poorly water-soluble API because part of the active dissolves in the binder solution and participates in liquid-bridge formation. However, when the bed is dried, dissolved active migrates to the granule surface and can produce a hard surface crust. This crust can increase tablet capping and lamination during compression if the granules are over-dried. A target granule LOD of 2.0–4.0% w/w is therefore maintained; over-drying below 1.5% w/w increases static charging and particle segregation, while residual moisture above 5.0% w/w can cause picking and sticking on tablet tooling. Dissolution testing of finished solid oral forms typically uses USP <711> apparatus II with paddle speed 75 rpm in 900 mL of buffered media selected according to the product monograph; the sodium salt generally shows rapid initial release, which may require disintegrant reduction relative to free-acid formulations.

Specification Profile and Compendial Test Methods

The following table lists representative release parameters for a non-sterile pharmaceutical grade; the current pharmacopoeial monograph applicable in the intended market is the governing document.

For injectable-grade material, additional controls include bacterial endotoxins, visible and subvisible particulate matter, and a low bioburden before sterilising filtration. The API manufacturer commonly provides a TSE/BSE statement, nitrosamine risk evaluation, and residual solvent declaration under ICH Q3C. In production-scale transfers between lots, moisture and particle-size distribution are the two most frequent sources of batch-to-batch variation, so incoming QC should include loss on drying and laser diffraction before the material is released for formulation.

Production-scale blending of sulphadimidine sodium for oral solids typically begins with screening through a 500 µm mesh sieve to break soft agglomerates. The material is charged to a double-cone or V-blender at 50–70% of vessel capacity and combined with microcrystalline cellulose, lactose monohydrate, croscarmellose sodium, and pregelatinised starch. Magnesium stearate is screened separately and added at 0.5–1.0% w/w for the final 3–5 minutes of blending; longer lubrication increases hydrophobicity and slows dissolution. For wet granulation, a binder solution of povidone K30 in purified water or hydroalcoholic vehicle is sprayed into a high-shear granulator at 2–5% w/w binder solids relative to dry mass. Granulation end point is determined by impeller power curve and visual mass consistency; over-wetting produces large agglomerates and solute migration during drying. Fluid-bed drying inlet air temperature is maintained at 50–60°C with bed temperature not exceeding 45°C to avoid discolouration; final granule loss on drying is controlled at 2.0–4.0% w/w. Milled granules are passed through an 800 µm oscillating granulator and lubricated. Tablet compression on a rotary press uses 8–10 mm round concave tooling, main compression force 5–15 kN, and precompression force approximately 10–20% of main force to reduce capping. Target tablet hardness is 50–80 N, friability ≤ 1.0% per USP <1216>, and disintegration ≤ 15 minutes in 0.1 M HCl per USP <701>. Capsule filling of the final blend is performed on a dosator or tamping-pin machine with acceptable weight variation ≤ 5% RSD and content uniformity acceptance value ≤ 15.0 per USP <905>. At relative humidity above 60%, pre-drying of the starting API and humidity-controlled suites are required because the sodium salt softens and cakes.

Dry granulation of sulphadimidine sodium is used when the API is moisture-sensitive or when the product particle-size distribution varies too much for direct compression. The powder is blended with ductile binders such as microcrystalline cellulose and compacted using a roller compactor with roll pressure 30–70 kN and roll gap 1.5–3.0 mm. The ribbons are milled through an 800 µm screen. Dry granulation minimises migration of the soluble active component because no liquid drying step is involved, but it can produce a bimodal granule distribution if the roll pressure is not controlled. The granules are then lubricated and compressed or filled into capsules.

Injectable processing of sulphadimidine sodium begins with dissolution in Water for Injections that has been sparged with nitrogen to limit carbon dioxide ingress. Carbon dioxide lowers solution pH and can precipitate the poorly soluble free acid; for this reason, the solution is maintained in closed stainless-steel or glass-lined equipment and exposed to ambient air as little as possible. The pH is adjusted to 8.5–10.5 with 1.0 M sodium hydroxide or hydrochloric acid. The solution is then filtered through 0.45 µm and 0.22 µm membrane filters, filled into Type I glass containers, and terminally sterilised at 121°C for 15 minutes if the formulation stability supports heat sterilisation. Aseptic filtration is used for formulations that cannot tolerate terminal heat exposure. Injectable-grade API should meet a low endotoxin limit, typically ≤ 0.50 EU/mg, and should be packaged to prevent particulate contamination. Oral liquids and syrups use the sodium salt to dissolve rapidly in a buffered vehicle. A vehicle pH of 5.0–7.5 balances chemical stability and palatability; amber glass or opaque HDPE packaging is used because sulfonamides are light-sensitive. Sodium metabisulfite at 0.1–0.5% w/v can act as an antioxidant, but sulfite must be declared and may be inappropriate in sulfonamide-sensitive patients. Contact with strong oxidising agents is avoided; alkaline solutions above pH 12 are not held for prolonged periods because of accelerated sulfonamide hydrolysis.

Production-scale storage of sulphadimidine sodium powder requires relative humidity below 60% and temperature below 25°C. When the material is stored in unopened double-bagged packaging with desiccant, moisture pick-up is negligible; once the bag is opened, the powder takes up moisture quickly. Weighing rooms should be set at 45–50% RH or lower, and the material should not remain open for more than 24 hours. Moisture content above 5.0% w/w is a typical rejection criterion because damp powder flows poorly, sticks to stainless-steel surfaces, and can generate high punch forces during compression. The stability of solid oral dosage forms containing sulphadimidine sodium is evaluated under ICH Q1A long-term and accelerated conditions; packaging should include an effective moisture barrier such as aluminium foil or PVC/PVDC blister. Light exposure accelerates discolouration; a light-resistant container is therefore used for bulk API and finished oral liquids.

When Sulphadimidine Sodium Replaces the Free Acid in Wet Granulation

Replacement of sulphadimidine base with the sodium salt changes the granulation-liquid demand and the spatial distribution of active substance in dried granules. The free acid requires wetting agent or surfactant because of poor aqueous contact; the sodium salt dissolves in the granulating fluid and reduces the quantity of fluid required to reach the granule coalescence endpoint. For a high-shear granulator, this means impeller power rises earlier in the water-addition curve. If the operator uses the liquid amount established for the free acid, the wet mass becomes over-wet, and the subsequent drying cycle must be extended. Over-wet processing produces large hard agglomerates that survive milling and cause content uniformity drift.

During fluid-bed drying, dissolved sodium salt migrates to the granule surface. A slow drying ramp with inlet air temperature 50–60°C and bed temperature 35–45°C is used to avoid surface crust formation. At high API loads above 20% w/w, a hydroalcoholic granulation vehicle of ethanol:water 70:30 v/v may be selected to reduce bulk dissolution of the sodium salt; published data for this specific configuration is limited. The replacement also changes the disintegration mechanism. Because the sodium salt hydrates rapidly, the tablet can disintegrate faster than the free-acid formulation at the same disintegrant level. Croscarmellose sodium is commonly reduced from 5% w/w to 2–3% w/w, and the dissolution profile is rechecked against USP <711> before process scale-up.

Contrasting Sulphadimidine Sodium with Sulphadimidine Base and Sulfadiazine Sodium

Sulphadimidine sodium is not directly interchangeable with the free acid or with other sulfonamide sodium salts. The counterion alters solubility, solution pH, and route suitability; the pyrimidine-ring substituents differ from sulfadiazine sodium and affect pharmacological and formulation properties. The table below summarises the major technical distinctions.

Sulphadimidine base remains a preferred option in markets where only the free acid monograph is recognised, but its poor aqueous solubility forces suspension or solid oral formulations. Sulfadiazine sodium provides high water solubility and is used in injectable applications, but its different molecular geometry and dissolution behaviour mean that equipment settings and granulation endpoints developed for sulfadiazine sodium cannot be transferred directly to sulphadimidine sodium without verification.

Sulphadimidine sodium is selected when aqueous solubility and flexible oral-to-injectable processing are required. Its operational boundaries include moisture control below 60% RH, protection from carbon dioxide, avoidance of strong oxidising agents, and limited exposure to pH values above 12. Direct substitution for the free acid or another sulfonamide salt requires revalidation of granulation, drying, dissolution, and stability parameters according to current pharmacopoeial and regulatory requirements.