Inactivated combined ovine/caprine braxy, struck and enterotoxaemia vaccine API is formulated into an aqueous aluminium hydroxide-adjuvanted injectable suspension used for subcutaneous immunisation of sheep and goats. The API is a formalin-inactivated whole-culture antigen concentrated from Clostridium septicum, Clostridium perfringens type C, and Clostridium perfringens type D; before release for downstream formulation it is titrated against reference antitoxin to establish the fill volume needed per final dose. Compliance standards governing this application include Ph. Eur. 0062 for vaccines for veterinary use, sterility testing by direct inoculation per Ph. Eur. 2.6.1, bacterial endotoxin limit evaluation per Ph. Eur. 2.6.14, and residual formaldehyde assay by a validated high-performance liquid chromatographic method. The formulation addition ratio is set by batch potency and is not fixed; a representative working range is 10–20% v/v of API concentrate, with the final aluminium concentration adjusted to 1.5–2.5 mg Al³⁺ per 2.0 mL dose. Downstream production proceeds by adding the API concentrate to a sterile aluminium hydroxide gel under low-shear impeller agitation at 100–300 rpm for 45–90 min, followed by pH adjustment to 6.5–7.0, mixing with phosphate-buffered saline, and filling through a peristaltic pump equipped with silicone tubing into siliconised Type I glass vials under a nitrogen overlay. The terminal product is an aqueous suspension for injection supplied in 2 mL, 10 mL, and 100 mL presentations; the 2 mL single-dose presentation is intended for subcutaneous administration to lambs, ewes, and goats. Tablet and capsule presentations are not considered valid downstream options for this parenteral antigen because oral delivery of inactivated clostridial toxoids has no demonstrated field efficacy.

What Lyophilisation Parameters Control Residual Moisture in Clostridial Antigen Powder for Injection?

Freeze-dried powder presentations of the combined API are produced when downstream vaccine manufacturers require a dry intermediate for reconstitution in remote flock handling conditions. The pre-lyophilisation bulk contains the API at a fill-volume target of 1.0 mL per vial, with trehalose at 2–5% w/v and mannitol at 1–3% w/v as cryoprotectants; the API addition ratio is calculated so that each single dose delivers 2.0 IU of Clostridium perfringens type D epsilon toxoid after reconstitution to 2.0 mL. Compliance standards include residual moisture by Karl Fischer titration per Ph. Eur. 2.5.12, sterility per Ph. Eur. 2.6.1, uniformity of mass of single-dose preparations per Ph. Eur. 2.9.5, and container closure integrity testing with a vacuum decay method. The downstream process begins with aseptic filling of the formulated bulk into 3 mL Type I glass vials, followed by lyophilisation in a production freeze-dryer. Shelf temperature is ramped from 4°C to -45°C at 0.5°C/min, held for 4 h, primary drying is performed at -20°C and 0.10–0.20 mbar for 20–28 h, and secondary drying is performed at 25°C for 6–10 h. Collapse temperature is pre-determined by freeze-drying microscopy, and product temperature is kept below the collapse value by controlling shelf temperature and chamber pressure. The terminal product is a white to off-white lyophilised plug for suspension for injection, reconstituted with 2.0 mL Water for Injections immediately before subcutaneous administration.

In sheep and goat vaccination programmes where multiple clostridial diseases occur concurrently, the combined braxy/struck/enterotoxaemia API is blended with separately produced inactivated Clostridium tetani, Clostridium novyi, and Clostridium chauvoei antigens to form a single multivalent clostridial vaccine. The combined API occupies 25–40% of the total antigen pool volume after potency adjustment, while each supplementary monovalent antigen is added at 5–15% of final bulk; these proportions are determined by reference antitoxin titration and are re-defined for each incoming API batch due to fermentation titre variation. Compliance follows Ph. Eur. 0062, bacterial endotoxin testing per Ph. Eur. 2.6.14, and stability study design aligned with VICH GL44. The downstream production process is sequential antigen adsorption onto aluminium hydroxide gel to avoid competitive displacement; each antigen is adsorbed at 4–8°C for 16–24 h before the next antigen addition, with pH maintained at 6.5–7.0 and the final suspension diluted to the target dose volume after all antigen feeds. Terminal product types are multivalent aqueous suspensions in 100 mL and 250 mL multi-dose polyethylene bottles, intended for subcutaneous flock vaccination of sheep and goats; published data for the exact blend ratio used in each geographical market are limited and must be generated by the formulator.

When Preservative-Free Aqueous Suspension Is Filled into Unit-Dose Syringes

Preservative-free aqueous suspension preparation for prefillable syringe lines requires the formulator to keep the aluminium hydroxide gel particle size distribution within narrow limits because nozzle clogging and syringe plunger drag are observed when the gel is overmixed or aged. The API is added to the sterile suspending vehicle at 10–18% v/v, and the vehicle is prepared with sodium chloride and sodium phosphate buffer to a final pH of 6.8–7.2; the resulting suspension has a viscosity of 15–35 mPa·s at 25°C and a shear rate of 50 s⁻¹, measured on a cone-plate rheometer. Compliance standards for this application are Ph. Eur. 2.6.1 for sterility, Ph. Eur. 2.6.14 for bacterial endotoxins, and ISO 7886-1 for single-use sterile hypodermic syringes when the final container is a prefillable syringe. The downstream filling process uses aseptic lines with ceramic piston pumps, in-line 0.22 µm filtration of the vehicle before API addition, and nitrogen flushing to a headspace oxygen level below 2.5%; line speed is typically limited to 6,000–10,000 units/hour to prevent aggregate formation in the pump head and to maintain fill weight uniformity. Terminal products are single-dose 1.0 mL and 2.0 mL prefillable syringes with attached needles for subcutaneous injection in sheep and goats.

When tropical distribution channels impose short-term cold-chain excursions above 25°C, the combined API can be converted into a granular premix that is reconstituted with sterile Water for Injections at the point of use. The granule matrix is composed of 85–90% w/w lyophilised antigen concentrate, 5–10% w/w maltodextrin as a bulking agent, and 1–3% w/w sodium chloride; the API addition ratio is calculated to produce a 1× suspension after reconstitution of the unit dose. Compliance standards include residual moisture below 3.0% by Karl Fischer titration per Ph. Eur. 2.5.12, uniformity of mass per Ph. Eur. 2.9.5, and microbial enumeration per validated compendial methods. Downstream processing is performed in a containment isolator at relative humidity below 30%, using dry granulation, sieving through a 1.0 mm mesh, and unit-dose filling into aluminium laminate pouches under vacuum. The terminal product is a granular premix for suspension for injection, intended for reconstitution under field conditions where liquid vaccine cold-chain logistics are restricted; the tablet and capsule powder grades are not used because no oral efficacy data support enteric delivery of this antigen.

Adjuvant Adsorption Kinetics in High-Titre Ovine/Caprine Injectable Suspensions

The formulation of high-titre suspensions from the combined API requires strict control of the protein-to-aluminium ratio because aluminium hydroxide gel has a finite adsorption capacity and its point of zero charge lies above pH 11.0. At the formulation pH of 6.8–7.0 the gel surface remains positively charged and adsorbs negatively charged clostridial toxoids; below pH 6.0 the gel begins to dissolve and releases adsorbed antigen. In this deep-dive configuration, the API is adjusted to 0.8–1.5 mg protein/mL in the final adsorption mixture, the aluminium hydroxide concentration is held at 2.0–3.0 mg Al³⁺/mL, and the API concentrate is added at 15–25% v/v of final bulk. Adsorption is performed at 4–8°C for 20–24 h at pH 6.8–7.0; unbound antigen is measured by size-exclusion high-performance liquid chromatography after 24 h, and the acceptance criterion is ≤10% unbound protein. Compliance is anchored to Ph. Eur. 0062 for vaccines for veterinary use, pH measurement per Ph. Eur. 2.2.3, and sterility per Ph. Eur. 2.6.1. The production process uses a rotor-stator mixer at 3,000–5,000 rpm for gel dispersion before antigen addition, followed by low-shear paddle agitation during the adsorption period to avoid reducing gel particle size and increasing settling. Terminal product is a high-titre suspension for injection; intramuscular administration requires local tolerance data because published data for this specific combined antigen in goats are limited.