In equine trypanosomiasis control programmes where national registrations of organoarsenical injectable products remain active, neoarsphenamine veterinary grade API is converted into sterile lyophilized vials at a unit content of 0.45 g or 0.60 g per vial, producing a dry-fill addition ratio of 100% w/w active substance when no bulking agent is included. Before lyophilisation, the aqueous compounding batch is prepared with nitrogen-sparged Water for Injection at 4–8 °C, held for no more than 8 h, and passed through a 0.22 µm PVDF membrane into amber Type I glass vials under ISO 14644-1 Class 5 conditions. The freeze-drier with 10.5 m² shelf area is programmed to freeze at -45 °C, primary drying at -25 °C for 20–24 h, and secondary drying at +25 °C until the residual moisture by Karl Fischer titration is ≤1.0% w/w per USP <921>. Container closure integrity is verified by USP <1207> vacuum decay, and sterility is confirmed by USP <71> membrane filtration. Residue compliance uses US FDA 21 CFR 556.60, with tolerances of 0.5 ppm in muscle and 2 ppm in liver and kidney, while elemental impurity control follows ICH Q3D(R2) arsenic Class 1 PDE of 15 µg/day. The finished dosage form is a powder for injection reconstituted to 4.5–6.0% w/v with 10 mL Water for Injection immediately before intravenous administration. Production line data show vial breakage rises above 1.3% when fill volume exceeds 3.2 mL or primary drying shelf ramp exceeds 0.5 °C/min.

What Limits the Drinking-Water Stability of Soluble Neoarsphenamine Granules in Poultry?

For avian spirochetosis caused by Borrelia anserina, the drinking-water route requires a granule master batch in which neoarsphenamine veterinary grade API is incorporated at 20.0% w/w on a lactose-mannitol carrier; the addition ratio is fixed at 20.0% w/w because higher loadings depress glass transition during fluid-bed drying and yield fines. Top-spray fluid-bed granulation on a 3.1 kg batch-capacity unit uses inlet air at 60 °C, product bed temperature of 36–40 °C, spray rate of 12–15 g/min/kg, and outlet air humidity ≤20% RH. After drying, the granules are screened through 0.8 mm and blended with sodium citrate dihydrate to buffer the final drinking-water solution at pH 6.5–7.0; the final drinking-water concentration is set at 0.02% w/v for a 24 h administration window. Loss on drying is controlled at ≤2.0% w/w by USP <731>, and microbial quality is evaluated by USP <61> because this is a nonsterile oral dosage form. Regulatory compliance for the finished product is based on EU Regulation 2019/6 and ICH Q3D(R2) arsenic Class 1 PDE 15 µg/day, while residue control for food-producing birds references US FDA 21 CFR 556.60 liver and kidney tolerances of 2 ppm. Finished product type is a water-soluble granule packed in aluminium-lined 1 kg sachets. Field observations from poultry houses show that when atomisation pressure falls below 1.5 bar, the fine particle fraction below 150 µm rises above 25%, and drinking-line nipple clogging increases measurably.

The tablet dosage pathway for companion animal spirochaetosis and trypanosomiasis presents a compaction problem because neoarsphenamine has low compactibility and darkens in the presence of moisture and reducing excipients. The core tablet formula contains 20 mg active per 200 mg tablet, an addition ratio of 10.0% w/w, with mannitol at 60.0% w/w, microcrystalline cellulose at 25.0% w/w, crospovidone at 3.0% w/w, colloidal silicon dioxide at 1.0% w/w, and magnesium stearate at 1.0% w/w; lactose is excluded because reducing sugars accelerate oxidative darkening. Wet granulation in a high-shear mixer runs at impeller 300 rpm and chopper 1500 rpm; the wet mass is screened through 1.0 mm, dried in a fluid-bed unit at inlet air 50 °C and product temperature 38–42 °C to loss on drying ≤2.0% w/w by USP <731>. Compression on a rotary tablet press with D-tooling operates at 8–12 kN compression force, producing tablet breaking force of 60–80 N by USP <1217> and disintegration time ≤15 min by USP <701>. Release testing includes content uniformity by USP <905> acceptance value ≤15 and dissolution by USP <711> with 900 mL of 0.1 M HCl at 50 rpm, Q=75% at 30 min. The terminal product is an immediate-release veterinary tablet packaged in amber glass or aluminium-PVC blister. Elemental impurity limits are set by ICH Q3D(R2) arsenic PDE 15 µg/day; if the tablet is administered to food-producing species, residue control follows US FDA 21 CFR 556.60. Operational boundaries include avoiding amine-based binders and disintegrants because free amine groups promote premature oxidative coupling, and extended compression dwell time below 8 kN increases weight variability due to poor granule flow.

If Terminal Sterilisation of Aqueous Neoarsphenamine Solutions Is Not Feasible, Aseptic Filtration Must Account for Oxidation Sensitivity

For regional markets that license a ready-to-use injectable solution rather than a lyophilized powder, the manufacturing route is aseptic filtration rather than terminal steam sterilisation because aqueous neoarsphenamine degrades rapidly at 121 °C, with published data for this specific configuration limited but forced-degradation studies indicating related-substance increase above 5% by HPLC area-normalisation after autoclaving. The formulation addition ratio is 50 mg/mL (5.0% w/v) active substance in nitrogen-sparged Water for Injection, with sodium metabisulphite at 0.1% w/v, and pH adjustment to 6.5–7.0 using dilute sodium hydroxide. The bulk solution is held at 4 ± 2 °C and filtered through 0.22 µm polyethersulfone membrane under ISO 14644-1 Class 5 conditions, then filled into amber glass ampoules or vials under sterile-filtered nitrogen overlay to headspace oxygen ≤0.5%. Sterility is confirmed by USP <71> with 14-day incubation, bacterial endotoxin limit is set at 0.5 EU/mg by USP <85>, and particulate matter is evaluated by USP <788>. Compliance includes ICH Q3D(R2) arsenic Class 1 PDE 15 µg/day, EU Regulation 2019/6, and US FDA 21 CFR 556.60 edible tissue tolerances where food-producing animals are treated. The finished product type is a sterile injectable solution for slow intravenous or intramuscular administration. Production line experience shows that dissolved oxygen exceeds 0.5 mg/L during tank transfer when the nitrogen sparge line pressure drops below 0.2 bar, causing darkening within 2 h; therefore, each transfer vessel is equipped with in-line oxygen probes.

In smallholder ruminant treatment programmes where parenteral administration is impractical and regulatory access to oral organoarsenical drench products remains, neoarsphenamine veterinary grade API is formulated as a water-soluble oral drench powder at an addition ratio of 5.0% w/w active substance on an acid-stabilised carrier composed of dextrose monohydrate 90.0% w/w, citric acid 3.0% w/w, and sodium metabisulphite 2.0% w/w. Dry mixing is performed in a 300 L twin-shell blender with intensifier bar at 20 rpm for 15 min; blend uniformity is controlled at relative standard deviation ≤5.0% by USP <905> blend sampling, and mixing times beyond 45 min are avoided because segregation of the high-density organoarsenical fraction increases. The powder is reconstituted in clean drinking water at 20 g/L (2.0% w/v) immediately before oral drench administration, and solutions are consumed or discarded within 2 h because oxidative degradation in unsparged water produces a colour shift and reduced assay. The terminal product type is a nonsterile powder for oral solution packed in moisture-resistant high-density polyethylene jars with desiccant. Compliance for nonsterile compounding follows USP <795>; water quality for reconstitution is verified to USP <1231>; and residual arsenic in food-producing ruminants is managed to US FDA 21 CFR 556.60 limits of 0.5 ppm in muscle and 2 ppm in liver and kidney. Elemental impurity control follows ICH Q3D(R2) arsenic PDE 15 µg/day. Compatibility limits exclude contact with hypochlorite-based sanitising solutions because free chlorine reacts rapidly with the trivalent arsenic centre.