Vitamin K₃ (menadione sodium bisulfite) veterinary-grade active pharmaceutical ingredient for tablets, injections, capsules, powders, granules, premixes, and solutions is supplied as a water-soluble addition compound of 2-methyl-1,4-naphthoquinone and sodium bisulfite. The material is a white to pale-yellow crystalline powder and is identified by CAS 130-37-0 for the anhydrous form and CAS 6147-37-1 for the trihydrate; the corresponding molecular formulas are C₁₁H₉NaO₅S and C₁₁H₉NaO₅S·3H₂O. The trihydrate contains theoretically 16.4% water and a menadione equivalent of 52.1% by molecular weight, while the anhydrous form contains 62.3% menadione equivalent. Because model numbers are manufacturer-specific, procurement specifications should identify the substance by CAS number and hydrate form rather than by commercial product code alone.

The API is used where vitamin K activity is required in poultry, swine, and companion animals. Pharmacological activity depends on conversion to menaquinone-4, which supports γ-carboxylation of glutamate residues in prothrombin and coagulation factors VII, IX, and X. Unlike vitamin K₁, menadione sodium bisulfite does not require bile-salt micellar solubilisation for absorption in most monogastric species, which permits formulation into aqueous drinking-water solutions and low-fat oral dosage forms. Typical release parameters include appearance, identification by high-performance liquid chromatography retention time, assay, loss on drying or water content, residue on ignition, heavy metals, and related substances. Assay acceptance criteria are commonly set at ≥96.0% for trihydrate material intended for parenteral formulation; feed-grade criteria may be lower and are not automatically suitable for injectable manufacture.

Primary veterinary indications include hypoprothrombinemia associated with coumarin rodenticide exposure, dietary deficiency, and hepatobiliary or malabsorptive conditions in which parenteral vitamin K is required. The sodium bisulfite form is used when rapid correction of prothrombin time is needed through injectable administration, followed by oral maintenance.

What Distinguishes Menadione Sodium Bisulfite from Other Vitamin K₃ Derivatives in Veterinary Dosage Manufacture?

Menadione base is practically insoluble in water and is not a practical active ingredient for aqueous injection or drinking-water premixes. The sodium bisulfite addition compound is freely soluble in water, which permits direct dissolution before wet granulation, dissolution into oral vehicles, and sterile filtration for parenteral manufacture. This is a formulation difference rather than a biological difference: all menadione salts serve as pro-drug sources of menaquinone-4 after tissue alkylation.

The selection of menadione sodium bisulfite over menadione nicotinamide bisulfite is based on the absence of the nicotinamide counter-ion when niacin supplementation must be controlled independently. In injectable and drinking-water solutions, the bisulfite moiety is redox-active and can reduce other susceptible actives if no compatibility screening has been performed. Vitamin K₁ has a phytyl side chain and is lipid-soluble; vitamin K₂ is a series of menaquinones with unsaturated isoprene side chains. Menadione sodium bisulfite lacks the side chain entirely and becomes active only after prenylation in tissue. This distinction explains why the product is classified as vitamin K₃ rather than a natural vitamin K source, and why its dose must be expressed as menadione equivalent to avoid potency errors across salt forms.

During steam conditioning ahead of pellet presses, exposure to moisture and elevated temperature can reverse the bisulfite adduct and release free menadione. The released menadione is then oxidised to inactive naphthoquinone degradation products. Production-scale experience indicates that conditioner retention time and pellet die temperature are more important than set steam pressure alone; published data for this specific configuration is limited. Premixes containing menadione sodium bisulfite should not be stored in direct contact with choline chloride or acidic mineral carriers because free moisture and trace metal oxides accelerate degradation. Residual moisture in finished premix or granular intermediates should be controlled below 5.0% before bagging when barrier packaging is not used, and pre-drying is required when ambient relative humidity exceeds 60% during open handling.

In aqueous systems, the bisulfite adduct is most stable under slightly acidic conditions; pH values above 7.0 promote dissociation and oxidative degradation. Chelation of trace copper and iron is beneficial in liquid formulations because free transition metals catalyse redox breakdown. Light exposure also degrades menadione solutions, so amber glass or opaque high-density polyethylene packaging is specified.

High-Shear Granulation and Direct Compression Operating Windows

For tablet and capsule manufacture, menadione sodium bisulfite is normally incorporated as a milled or sieved powder at a low drug load. Blend uniformity requires particle-size overlap with the excipient system. In direct compression, drug-rich agglomerates are resolved by passing the blend through a 500 µm sieve before lubrication; over-processing in high-shear mixers can generate fines that segregate under vibration. Granulation endpoint is controlled by gravimetric moisture and impeller torque rather than time alone.

Tablet processing with microcrystalline cellulose and dicalcium phosphate dihydrate is feasible when final granule moisture is maintained between 1.5% and 3.0%. Magnesium stearate lubrication levels above 1.0% are avoided because hydrophobic lubricant films extend disintegration times and reduce dissolution of the water-soluble API. Compatibility screening is required in fixed-dose combinations with choline salts, reducing sugars, or amine-containing excipients because early discoloration indicates adduct decomposition.

Compressed tablets and capsules should be evaluated against USP <905> for weight variation, USP <701> for disintegration, and USP <711> for dissolution, with species-specific media selected according to the target animal.

Multi-component vitamin/mineral premixes are produced by stepwise dilution from a micro-ingredient premix. Menadione sodium bisulfite is usually added after trace minerals have been dried and cooled; direct addition onto freshly dried mineral oxide carriers can produce darkening and loss of assay. Ribbon blender or twin-shaft paddle mixers are preferred over high-shear mixers for final premix blending because long mixing times in high-shear equipment raise product temperature and promote degradation. When powders and granules are packed in non-barrier liners, storage at ambient temperature above 30°C is not recommended for prolonged distribution cycles.

For oral solutions and drinking-water formulations, the API is dissolved in deionised water with a suitable antioxidant system. Stock solutions should be protected from light and used within the hold time established by stability-indicating high-performance liquid chromatography. The product is not interchangeable with oil-based phytomenadione injections without reformulation because the solvent system and biodistribution differ.

When Menadione Sodium Bisulfite Is Selected for Injectable Solutions

Parenteral formulations require water for injection, control of pH, osmolality, particulate matter, and bacterial endotoxins, and a sterilisation strategy matched to the heat sensitivity of the API. Menadione sodium bisulfite solutions are susceptible to heat-induced degradation; aseptic filtration through 0.22 µm membrane filters is therefore used instead of terminal steam sterilisation when heat stress exceeds the stability window. Finished solutions are filled under nitrogen or argon headspace to reduce oxidative degradation, and the container closure system is selected to minimise oxygen ingress.

Compliance testing includes USP <1> for injectable preparations, USP <788> for subvisible particulate matter, USP <790> for visible particulates, and USP <85> for bacterial endotoxins. Osmolality is adjusted with sodium chloride or dextrose and verified by freezing-point depression according to USP <785>. Published data for terminal steam sterilisation of this specific low-volume parenteral configuration is limited; thermal mapping and degradation profiling should precede any change from aseptic filtration to moist-heat cycles.

The following release and process-control methods are applied by dosage form; inclusion does not imply that every batch is tested against every method unless the product specification requires it.