For sterile aqueous subcutaneous immunotherapy, allergen veterinary-grade API is received as a concentrated extract and transferred from single-use polypropylene containers into a 20±2°C controlled suite. The bulk extract passes through a 0.45 µm polyethersulfone prefilter and a 0.22 µm PVDF sterilizing filter; filtration pressure is held below 1.0 bar to avoid protein aggregation. Final therapeutic dilutions are prepared as 1:50,000, 1:25,000, 1:10,000, and 1:5,000 w/v strengths, with maintenance volumes of 0.2–0.5 mL injected subcutaneously at 14–28 day intervals. The vehicle contains 0.9% w/v sodium chloride and 0.4% w/v phenol, adjusted to pH 6.3–7.0 with 0.1 M hydrochloric acid or sodium hydroxide and verified using a two-point calibrated pH meter at 25°C. Major allergen content is measured by inhibition ELISA against an in-house reference standard, with batch acceptance limits of ±20% of label claim. Phenol preservative content is quantified by reversed-phase HPLC on a 150×4.6 mm C18 column at 25°C with UV detection at 270 nm. Filter integrity is confirmed by bubble point testing before and after filtration, and final product endotoxin is controlled to ≤0.5 EU/mL by kinetic chromogenic LAL per Ph. Eur. 2.6.14. Aqueous therapeutic solutions are packed into 5–10 mL Type I glass multi-dose vials with silicone-treated chlorobutyl stoppers and stored at 2–8°C. Autoclaving is excluded for final sterilization because most allergen proteins denature at temperatures above 60°C; the manufacturing area must therefore maintain Grade C or equivalent controlled conditions under EU GMP Annex 1. Batch sizes commonly range from 5 L to 50 L, with scaling limited by sterile filter capacity and the need to maintain laminar flow conditions during dispensing.

Why does aluminium hydroxide adsorption change the subcutaneous depot profile of veterinary allergen APIs?

Aluminium hydroxide-adsorbed therapeutic suspensions are produced by mixing the aqueous allergen extract with a 1.0–2.0% w/v aluminium hydroxide wet gel at 2–8°C under low-shear stirring at 50–80 rpm for 60–90 min. The binding reaction is pH-dependent; adsorption of acidic allergen fractions is favoured at pH 6.0–6.5, where the aluminium hydroxide surface carries a positive charge. At pH above 7.0, the surface charge becomes less positive and binding may decline. Residual unadsorbed allergen is separated by ultrafiltration with a 10 kDa molecular weight cut-off and quantified by BCA assay or allergen-specific ELISA; the unbound fraction is normally required to be ≤10% of the total dose. Adsorbed products are used for depot immunotherapy because antigen release from the aluminium matrix is slower than from aqueous solution, allowing maintenance injection intervals of 3–4 weeks instead of 2–3 weeks. The suspension is filled into multi-dose vials with a target fill volume of 5–10 mL; resuspendability is tested by manual inversion 10–15 times followed by visual inspection. Viscosity measured with a cone-and-plate viscometer at 25°C stays below 15 mPa·s, and injection through a 25 G needle is not obstructed. Cold-chain distribution at 2–8°C is mandatory; freeze-thaw cycles break the aluminium hydroxide gel structure and produce irreversible sediment that cannot be redispersed by shaking. Phosphate buffer is avoided in Al-adsorbed allergen suspensions because phosphate ions displace adsorbed proteins from aluminium hydroxide via ligand exchange, causing a rapid drop in bound antigen.

Lyophilized injection-grade powders are specified when aqueous allergen solutions demonstrate potency drift or visible precipitate formation after 6 months at 2–8°C. The concentrated allergen API is formulated with trehalose or mannitol at 3–8% w/v as a glass-forming cryoprotectant and sterile-filtered through a 0.22 µm PVDF membrane before filling into 5–10 mL Type I glass vials. Freeze-drying uses a stainless-steel lyophilizer with a shelf ramp of 0.5°C/min from −40°C to −20°C, primary drying at −20°C under 0.08–0.12 mbar for 18–24 h, and secondary drying at 25°C for 6–8 h. Residual moisture is measured by coulometric Karl Fischer titration per Ph. Eur. 2.5.12 and must remain ≤2.0% w/w. Reconstitution with 0.9% sodium chloride injection should produce a clear to slightly opalescent liquid within 60 s at 20–25°C. Phosphate-buffered saline is not used as a reconstitution diluent because sodium phosphate crystallization during freezing causes pH shifts and can destabilize the allergen. The lyophilized format is selected for protease-rich mould and mite allergen mixes because solid-state glass matrices reduce hydrolytic degradation during storage. The allowable shelf-life is typically 24–36 months at 2–8°C when moisture ingress is prevented by bromobutyl stoppers and aluminium flip-off seals; however, stability for each new allergen source must be confirmed by real-time lot monitoring.

Orodispersible tablet matrices engineered for sublingual allergen delivery in cats

Sublingual allergen tablets are manufactured by blending the allergen dry premix with mannitol, microcrystalline cellulose, crospovidone 2–5% w/w, and magnesium stearate 0.5% w/w in a bin blender at 25 rpm for 10–15 min. Direct compression is performed on a rotary tablet press with 8–10 mm flat-faced tooling at 10–18 kN compression force. The target hardness is 25–50 N, measured on a calibrated hardness tester, and disintegration is ≤60 s in 900 mL water at 37°C per Ph. Eur. 2.9.1. The allergen dose is verified by extraction and ELISA with a content uniformity acceptance value ≤15 per Ph. Eur. 2.9.40. The powder bed is maintained at 30–35% relative humidity and 20±2°C during compression because higher moisture promotes mannitol crystallite bridging and die-wall adhesion. Sodium starch glycolate is not used as the primary disintegrant at levels above 5% w/w because its hygroscopicity can activate the allergen matrix prematurely and reduce tablet robustness. Packaging in aluminium/aluminium blister cavities is required; PVC/PVDC blister material is insufficient for moisture protection beyond 6 months in tropical climates. Room-temperature stability claims of 24 months at 25°C and 60% RH are conditioned on real-time stability data and monthly disintegration testing during the first 6 months of production.

Hard capsule dosage forms are compounded when veterinary practitioners require patient-specific allergen potencies outside fixed tablet strengths or for oral immunotherapy induction in dogs that reject sublingual tablets. The allergen API is first triturated with lactose monohydrate in a geometric dilution series from 1:10 to 1:100 w/w, then mixed with microcrystalline cellulose and 0.5% w/w magnesium stearate in a V-blender at 25 rpm for 15 min. The final powder is filled into size 3 or 4 hypromellose capsules at 100–150 mg target fill weight; in-process weight variation is checked on 20 capsules every 15 min, with acceptance of ±5% from mean weight. Allergen content uniformity is analyzed by phosphate-buffered saline pH 7.4 extraction and ELISA, with an RSD limit of ≤15% across 10 capsules. The filling suite is held at 20±2°C and 30–35% RH to prevent hygroscopic clumping and capsule shell brittleness. Mortar pre-rinsing with 1 g lactose blank is used to reduce surface binding of the allergen to the trituration vessel; without this step, allergen recovery in the final capsule can fall below 90% of the intended dose. Hard hypromellose capsules are preferred over gelatin for allergen stability because cross-linking of gelatin by residual aldehydes in some plant allergen extracts can delay dissolution. Filled capsules are placed in high-density polyethylene bottles with desiccant and stored at 2–8°C unless data support room-temperature stability.

When dry granules and premix intermediates are required for solid oral veterinary formulations

Wet granulation is selected when direct compression of low-dose allergen blends shows segregation, poor flow, or content uniformity failures. The allergen concentrate, either spray-dried onto lactose or presented as a freeze-dried milled powder, is combined with povidone K30 2–4% w/w as binder and granulated with purified water at 10–15% w/w liquid addition in a high-shear granulator with impeller speed 200 rpm and chopper speed 1,500 rpm. The wet mass is passed through a 0.8–1.25 mm screen and dried in a fluid-bed dryer with inlet air at 45±5°C until loss on drying is ≤5.0% per Ph. Eur. 2.2.32. The dried granules are blended with croscarmellose sodium 2% w/w and lubricated with sodium stearyl fumarate 0.5% w/w before compression or capsule filling. Sieve analysis requires ≥85% of material between 125 µm and 1,000 µm; oversized granules are re-milled through a 0.8 mm screen and re-sieved. Premix intermediates are packaged in aluminium-laminated bags with desiccant and stored at 2–8°C; reconstitution for oral solution is performed with 10–20 mL of 0.9% sodium chloride or sterile water at the point of dispensing. The granulated premix is also used to prepare multi-allergen veterinary tablets by mixing granules of different allergen species at defined w/w ratios. This format reduces dust formation and cross-contamination during transfer compared with raw milled APIs.

For intradermal allergy testing in dogs and horses, allergen veterinary-grade API is diluted into a glycerinated aqueous vehicle containing 50% v/v glycerol and 0.4% w/v phenol. The glycerol concentration stabilizes allergen proteins against surface adsorption and maintains microbiological quality during repeated withdrawal from 5–10 mL multi-dose vials. Diagnostic dilutions are typically prepared at 1:1,000 or 1:5,000 w/v for pollen, mite, and mould allergens; histamine phosphate 1:100,000 w/v serves as positive control, and glycerinated saline serves as negative control. The test solution is injected intradermally at 0.05–0.10 mL per site using a 27 G needle; immediate wheal and flare reactions are read at 15–20 min and delayed reactions at 24 h. Sterility is achieved by aseptic filtration through a 0.22 µm PVDF membrane; because 50% glycerol roughly doubles viscosity, the filter area is increased to 2–3× the area used for aqueous solutions of equal batch volume. The solution is not intended for subcutaneous therapeutic use at diagnostic volume because the high glycerol content can produce injection-site pain and irritation. Stability is assigned by real-time monitoring at 2–8°C for 12–24 months with allergen-specific ELISA and pH checks every 6 months; published data for some veterinary allergen species in this exact glycerinated configuration is limited.