Product code RXF-VET-IM-API-220 denotes a sterile micronized rifaximin active pharmaceutical ingredient prepared for veterinary dosage form manufacture across intramammary infusion suspensions, tablets, injectable preparations, capsules, powders, granules, premix, and non-aqueous solutions. The molecule is 4-deoxy-pyrido[1′,2′:1,2]imidazo[5,4-c]rifamycin SV, CAS 80621-81-4, molecular weight 785.88 g/mol, and appears as a reddish-orange to orange-brown crystalline powder. It is practically insoluble in water, freely soluble in dichloromethane, slightly soluble in ethanol, and sparingly soluble in acetone, which limits aqueous solution formulation unless co-solvent or complexation strategies are used. The grade is controlled for bacterial endotoxin, sterility, particle size distribution, residual solvents, heavy metals, and water content to support both aseptic intramammary preparation and oral solid dosage form manufacture in veterinary facilities operating under EU GMP Part II or equivalent. The material is not interchangeable with unmicronized oral rifaximin API because the intramammary specification imposes a D90 particle size control measured by laser diffraction according to ISO 13320:2020 and a sterile claim supported by Ph. Eur. 2.6.1. The low endotoxin acceptance limit of < 0.050 EU/mg is derived from the requirement to avoid pyrogenic reaction after intramammary administration, and the sterile micronized particle population is intended to remain suspended in oleaginous vehicles long enough to deliver the dose from a single-dose intramammary syringe.

Which compendial and sterility limitations distinguish RXF-VET-IM-API-220 from oral rifaximin API?

Compliance assessment includes the USP Rifaximin monograph, Ph. Eur. methods for sterility and endotoxin, and ICH residual solvent classes. Batch-to-batch variance in micronized rifaximin is evaluated by laser diffraction and scanning electron microscopy because particle agglomeration during micronization can shift the D50 and D90 values, altering syringeability in oleaginous intramammary vehicles. The production line uses a nitrogen-inerted spiral jet mill with grinding nozzle pressure maintained within the validated range; feed rate is reduced when inlet humidity exceeds 60 % RH because adsorbed moisture promotes particle agglomeration. Milling is followed by classification and packing under Grade C cleanroom conditions according to ISO 14644-1:2015; aseptic filling of final intramammary suspensions is performed under Grade A conditions at the point of fill. The sterile API is claimed sterile with a sterility assurance level of 10⁻⁶ when gamma irradiation is used as the terminal sterilisation step for the drug substance. Dry heat sterilisation at 160 °C for 120 min is not used because micronized rifaximin may show colour change and related substance increase under these conditions; gamma irradiation above 25 kGy is avoided because degradation products may increase. Table 1 lists batch release controls. Table 2 summarises the interchangeability constraints against conventional oral veterinary rifaximin grades.

In addition to the tabulated controls, the intramammary grade is audited for absence of β-lactam cross-contamination because rifaximin may be processed in facilities that also handle cephalosporin or penicillin APIs. Cleaning validation follows EMA guidance and uses a target carryover limit based on the permitted daily exposure of the most toxicologically active compound. The sterile API is supplied in double low-density polyethylene liners inside aluminium foil laminate; the foil provides a moisture vapour transmission rate below 0.01 g/m²/day at 38 °C/90 % RH and an oxygen transmission rate below 0.01 cm³/m²/day/atm, according to ASTM F1249 and ASTM D3985. This barrier is required because the micronized material adsorbs moisture above 60 % RH, leading to agglomeration and loss of syringeability. Unmicronized oral grade rifaximin is often packed in non-barrier fibre drums and is not suitable for aseptic processing without further micronization and sterilisation.

Direct compression of RXF-VET-IM-API-220 into veterinary tablets is not recommended as a primary route because the micronized D90 ≤ 20 µm population reduces bulk density and flow, typically requiring forced-cage or power-assisted feeders on rotary tablet presses. The powder has high specific surface area and is sensitive to moisture adsorption above 60 % RH; pre-drying in a vacuum tray dryer at 40 °C ± 2 °C for 4–6 h is required when water content exceeds 2.5 %. For capsule filling, tamping-force settings on an automatic capsule machine are adjusted because the micronized powder compresses under excessive tamping, causing weight variability. In one production scenario, a dosator nozzle capsule filler is preferred over tamping-disc machines when the formulation is a simple trituration with lactose monohydrate, because the dosator ejector pin compresses the powder column to a defined height rather than repeatedly tapping the bed. The powder blend should be characterised by angle of repose, bulk density, tapped density, and compressibility index according to USP <1174> before compression. Published data for this specific configuration is limited; therefore each blend must be qualified on the intended rotary press at minimum compaction force and speed settings to avoid punch binding due to particle adhesion to tooling surfaces.

If intramammary syringeability is to be maintained after high-shear dispersion

Intramammary infusion suspensions generally formulate the sterile micronized API in an oleaginous or gel vehicle. High-shear rotor-stator mixing is used to deagglomerate the micronized powder; impeller tip speed and residence time are limited because prolonged shear above 60 °C or repeated passes can induce vehicle viscosity loss and particle aggregation. A representative development protocol uses a rotor-stator mixer at 3000 min⁻¹ for 15 min while maintaining the vessel at 20 °C ± 2 °C. After mixing, the suspension is passed through a 150 µm inline screen and filled under aseptic conditions into single-dose intramammary syringes. Syringeability is assessed by measuring ejection force through a 24 G cannula at 25 °C; the target range is formulation-specific, and published data for this specific configuration is limited. Rheological evaluation according to ISO 3219 records yield stress and plastic viscosity because both parameters control retention in the udder cistern and removal by milking. A pronounced yield stress can prevent sedimentation but may also increase ejection force, so a controlled-stress rheometer is used to measure the cross-over stress where the elastic modulus G′ becomes equal to the viscous modulus G″; formulations are adjusted to keep this value low enough for syringability while avoiding hard settling. Terminal moist-heat sterilisation at 121 °C is not applied to rifaximin suspensions because stability data under saturated steam for this molecule are limited; aseptic processing and sterile API input are therefore mandatory. Particle size during scale-up is monitored because micronized rifaximin tends to form loose agglomerates that are not fully dispersed by low-shear planetary mixers; a rotor-stator mixer with a screen-type stator is specified rather than a simple propeller agitator.

For premix and granule applications, RXF-VET-IM-API-220 is blended with lactose monohydrate or microcrystalline cellulose and wetted with polyvinylpyrrolidone solution in a high-shear granulator. The wet mass is passed through a 1.0 mm screen and dried in a fluid-bed dryer at inlet air temperature 55 °C ± 3 °C until loss-on-drying is ≤ 2.0 %. Granule sieve distribution is controlled between 150 µm and 850 µm; oversize granules are dry-milled and re-screened. The micronized API tends to segregate in low-drug-load premixes if the carrier particle size differs widely, so a two-stage geometric dilution step is required before final blending. For extruded granule forms, a twin-screw extruder with a length-to-diameter ratio of 25:1 and segmented conveying elements is used without kneading blocks in the first barrel zone to avoid frictional heat above 40 °C; the die plate is sized to 0.8 mm and spheronisation is performed at 800–1200 rpm in a spheronizer for 2–5 min. Blend uniformity validation should follow USP <905> or an equivalent veterinary standard, and published data for this specific configuration is limited until process qualification is completed.

Injectable and solution handling requires non-aqueous vehicle selection

Rifaximin is practically insoluble in water, so injectable solutions are constrained to non-aqueous vehicles or co-solvent systems. The API dissolves slowly in propylene glycol, benzyl alcohol, and certain glyceryl esters; dissolution is accelerated by heating to 40 °C ± 2 °C under nitrogen, but prolonged heating above 50 °C should be avoided because degradation products may increase. For injectable suspensions, the sterile micronized powder is wetted with the vehicle under aseptic conditions and deagglomerated using a high-shear mixer. Terminal sterile filtration of the final suspension is not feasible because the suspended particles exceed the sterilising filter pore size; therefore the drug substance must be sterile and aseptic processing is mandatory. The final injectable product is filled in amber glass vials under nitrogen. Subvisible particulate matter is controlled according to USP <788>, with limits for particles ≥ 10 µm and ≥ 25 µm applied to the reconstituted or diluted suspension. This formulation type is not interchangeable with oral powders because the non-aqueous vehicle must be selected for tissue irritation and depot release. Stability studies should follow ICH Q1A(R2) with photostability testing under ICH Q1B; published data for this specific configuration is limited.

Packaging for tropical veterinary distribution uses double low-density polyethylene liners inside a foil laminate pouch, sealed under nitrogen; a desiccant sachet is added when water content exceeds 2.5 %. The material is photolabile in solution, so primary packaging for ampoules or vials is amber glass or opaque polymer. Storage is specified at 2–8 °C for the sterile intramammary grade, with transport excursions not exceeding 25 °C for more than 48 h. Shipment containers include temperature loggers calibrated to ISO 17025; excursions above 25 °C for more than 48 h require stability assessment before use. The product is not stored in unlined high-density polyethylene drums because oxygen permeability and electrostatic attraction of micronized powder cause wall losses. Compatibility with amine-functional excipients must be tested before solution formulation because rifaximin can exhibit oxidative degradation in alkaline media. Each lot is shipped with a certificate of analysis documenting the batch release controls listed in Table 1 and a tamper-evident seal on the outer aluminium pouch.