Closantel Sodium Dihydrate BP Vet is a salicylanilide anthelmintic active with a molecular weight of approximately 721.06 g/mol for the dihydrate sodium salt and 663.07 g/mol for the free acid. The base-equivalent conversion factor is 1.087; therefore a formulation claim of 50 mg/mL closantel base requires 54.35 mg/mL of Closantel Sodium Dihydrate. The API is processed into non-sterile oral and sterile injectable veterinary finished products, with particle-size control, headspace oxygen, and water activity forming the critical quality attributes across all routes. Terminal dosage forms covered are oral suspension, injectable solution, tablet/bolus, oral granule, and hard capsule. Manufacturing ranges are stated only where a parameter is externally verifiable; where published data for a specific configuration are limited, that limitation is stated explicitly.

Table 1: Closantel base-to-dihydrate salt conversion across standard label claims.

Oral Drench Suspension at 50 mg/mL: Dispersion, Viscosity, and Preservative Limits

Compliance for this non-sterile oral liquid is anchored to BP (Vet) assay acceptance criteria of 95.0–105.0 % of label claim, Ph. Eur. 5.1.4 microbial enumeration limits for oral liquids with total aerobic microbial count ≤ 10² CFU/mL, total yeast and mould count ≤ 10¹ CFU/mL, and absence of Escherichia coli, and stability protocols aligned to VICH GL3. The labelled concentration of 50 mg/mL closantel base is obtained with 54.35 mg/mL Closantel Sodium Dihydrate. The vehicle typically contains polysorbate 80 at 0.1–0.3 % w/v as wetting agent, xanthan gum at 0.25–0.40 % w/v as suspending agent, sodium methyl hydroxybenzoate at 0.15 % w/v and sodium propyl hydroxybenzoate at 0.015 % w/v as preservatives, and a phosphate or citrate buffer to a final pH of 7.0–8.0. Processability requires that the API be air-jet milled to a particle size of D90 ≤30 µm verified by laser diffraction per Ph. Eur. 2.9.31 or ISO 13320:2020; unmilled material with a bimodal distribution above 75 µm accelerates sedimentation and produces caking at the container base. The manufacturing sequence is high-shear dispersion: the wetting agent is first dissolved in purified water, the milled API is added through a 180 µm screen into a rotor-stator mixer operated at 2,800–3,200 rpm for 20–30 min, and the hydrated xanthan gum is incorporated under reduced shear to reach an apparent viscosity of 300–500 mPa·s at 20 °C and 10 s⁻¹. Deaeration is conducted at −0.08 MPa until entrapped air is removed, followed by filling into HDPE multidose bottles with graduated dosing chambers. Terminal finished types are 1 L, 2.5 L, and 5 L drench packs for sheep and cattle, and single-dose oral syringes for lambs. A known boundary is that xanthan gum systems should not be exposed to high concentrations of trivalent cations or strong oxidisers because viscosity can collapse or the active can degrade.

Where parenteral administration is selected, the sodium dihydrate form allows formulation of an aqueous injection at 50 mg/mL closantel base without reliance on lipophilic cosolvents, but the salicylanilide oxidation and the multidose container format impose headspace oxygen and preservative limitations. The batch release framework includes Ph. Eur. 2.6.1 sterility, Ph. Eur. 2.6.14 bacterial endotoxin control with a limit justified by the maximum daily dose and route, Ph. Eur. 5.1.1 sterilising filtration or terminal sterilisation validation, ICH Q3D elemental impurity control for parenteral products, and EU GMP Annex 1 requirements for closed aseptic filling of glass vial lines. A representative formulation contains 54.35 mg/mL Closantel Sodium Dihydrate, propylene glycol at 10–20 % v/v as a water-miscible stabilising cosolvent, benzyl alcohol at 1.0–1.5 % w/v as preservative in multidose vials, and a trometamol or sodium hydroxide adjuster to pH 8.5–9.0. Dissolution is performed under vacuum and nitrogen protection because the dihydrate salt is hygroscopic and the ionised salicylanilide is sensitive to oxidative discolouration; residual oxygen in the liquid should be below 0.5 mg/L before filtration. The bulk solution is filtered through 0.22 µm polyethersulfone membranes selected for low extractables and compatibility with alkaline pH, then aseptically filled into Type II amber glass vials. If terminal moist-heat sterilisation at 121 °C for 15 min is claimed, the manufacturer must demonstrate assay loss below 2 % and no increase in subvisible particulate matter under Ph. Eur. 2.9.19; published data for terminal sterilisation of this specific active are limited, so aseptic filtration is the more commonly reported route. Finished presentations are 50 mL, 100 mL, and 250 mL multidose vials sealed with chlorobutyl rubber stoppers and aluminium flip-off caps, and 500 mL collapsible pack formats where regional labels permit. An operational boundary is the incompatibility of the active at acid pH with oily vehicles: the free acid partition can shift, and precipitation occurs if the pH falls below the pKa region without sufficient ionisation.

What Compaction Force Window Prevents Lamination in 500 mg Base Boluses?

Compressed tablet and bolus formats for sheep and cattle require management of a high active load and the 1.087 salt factor, which increases core weight and reduces the room for functional excipients. Release specifications for a 500 mg closantel base bolus should include Ph. Eur. 2.9.5 uniformity of mass for single-dose preparations, Ph. Eur. 2.9.3 dissolution in a surfactant-containing medium, and Ph. Eur. 2.9.36 powder flow evaluation for pre-compression blends. The active content is 543.5 mg Closantel Sodium Dihydrate per unit, equivalent to 45.3 % w/w in a 1,200 mg core. A direct compression route is generally not feasible because the API exhibits poor flow and high punch adhesion; therefore wet granulation is used with povidone K30 at 3–5 % w/w as binder, microcrystalline cellulose at 20–30 % w/w as deforming filler, lactose monohydrate at 15–20 % w/w, croscarmellose sodium at 3 % w/w, and magnesium stearate at 0.75 % w/w. Granulation should be discharged at a loss-on-drying of 2.0–3.0 % after fluid-bed drying at 55–65 °C inlet temperature; over-dried granule below 1.0 % moisture increases friability and capping, while residual moisture above 4.0 % leads to picking and edge splitting. Compression on a rotary press should produce tablets with hardness 100–180 N, friability below 1.0 %, and ejection force below 8 kN to protect tooling. Because the active is light-sensitive and hygroscopic, film coating with an aqueous gastric-soluble polymer system at 3.0–4.5 % weight gain is applied. Terminal finished types are scored 250 mg and 500 mg base tablets for ovine and caprine dose titration, and uncoated or film-coated 1,000 mg ruminant boluses for cattle. Long disintegration times above 30 min in batch testing indicate insufficient croscarmellose sodium hydration or over-lubrication from hydrophobic magnesium stearate.

Granulation for single-dose oral reconstitution addresses operator exposure to dusty active, particle segregation during sachet filling, and the need for rapid wetting in a field-ready suspension. The granule intermediate is not an anhydrous stable form; water activity must be controlled to maintain microbial and chemical stability under tropical distribution. Compliance testing follows Ph. Eur. 5.1.4 for non-sterile oral preparations, Ph. Eur. 2.9.3 dissolution after reconstitution, and sieve analysis per Ph. Eur. 2.9.38 to control the granule fraction between 150 µm and 710 µm. A single-dose sachet labelled at 500 mg closantel base carries 543.5 mg Closantel Sodium Dihydrate. With a total fill weight of 2.5 g, the active load is 21.7 % w/w; higher active loadings above 30 % w/w reduce granule strength and increase dust. The formulation consists of maltodextrin or lactose monohydrate as water-soluble carrier, povidone K30 at 3–5 % w/w as aqueous granulation binder, crospovidone at 2–4 % w/w as disintegration aid, and colloidal silicon dioxide at 0.2–0.5 % w/w as flow aid. Processing is wet granulation in a high-shear mixer followed by fluid-bed top-spray drying at inlet 55–65 °C to a final moisture of 1.5–2.0 % by Karl Fischer titration per Ph. Eur. 2.5.12, with in-process sieve retention of 150–710 µm. Sachet filling is conducted at relative humidity below 40 % and sealed with low-moisture barrier laminate; desiccant is required where the package has water vapour transmission rates above 0.1 g/m²/day. Terminal dosage forms are single-dose sachets reconstituted in 50 mL potable water immediately before oral administration to sheep or calves, and bulk granules for metered dose delivery in specialised applicators. The boundary condition is moisture ingress above 2.5 %, which produces granule softening and a loss of free-flowing character during field use.

Hard Capsule Fill Weight and Dose Titration in Small Ruminants

For low-dose individual animal presentation, capsule filling is used mainly where a lamb or goat dose can be titrated without multi-dose liquid handling and where the active load remains below the flow limit of automatic capsule machines. Batch release testing for capsules uses Ph. Eur. 2.9.5 uniformity of mass, Ph. Eur. 2.9.3 dissolution, and Ph. Eur. 2.9.36 powder flow evaluation of the filled blend; if the product is registered as a single-dose veterinary product, storage stability follows VICH GL3 protocols. A 250 mg closantel base capsule requires 271.75 mg Closantel Sodium Dihydrate, which is 67.9 % w/w of a 400 mg fill. The remaining filler is microcrystalline cellulose at 20–30 % w/w, sodium starch glycolate at 4 % w/w, colloidal silicon dioxide at 0.5 % w/w, and magnesium stearate at 0.5–1.0 % w/w. Dry blending is performed in low-shear tumble mixers, and filling is carried out on an automatic tamping-pin capsule machine at 20–25 °C and 35–45 % RH to prevent shell brittleness and static charging. Terminal finished types are size 0 or 00 hard gelatin or HPMC capsules, often packed in aluminium foil blisters with desiccant. A process boundary is that powder blends with active above 70 % w/w show poor flow and require forced feed, while hygroscopic uptake above 4 % in gelatin shells causes shell deformation and delayed dissolution.