What Does the D90 Limit Mean for Capsule Content Uniformity in Low-Dose Veterinary Products?

Low-dose veterinary capsule filling places the granule API into a category where particle size distribution determines content uniformity more than the mean assay. A D90 above 150 µm after dry milling creates superpotent and subpotent pockets in the powder bed because the dosage unit mass is deliberately low. For a nominal fill weight of 250 mg and an API load of 10.0% w/w, the absolute API mass per capsule is 25 mg; a D90 shift from 140 µm to 210 µm raises the risk that the blend relative standard deviation exceeds 5.0% on the USP <905> uniformity of dosage units test. Production-scale filling with an intermittent capsule machine at 3,000–5,000 capsules/h is more sensitive to blend stratification than continuous filling at the same speed, because hopper resonance and die-table vibration compact fines near the auger discharge. The resulting fill weight drift is observed as a negative bias when the hopper level falls below 30% of working volume.

Compliance references for this route include Ph. Eur. 2.9.40, USP <905>, Ph. Eur. 2.9.1 for shell disintegration, and Ph. Eur. 2.9.3 for dissolution. The capsule shell must meet moisture limits, and the filled product must be protected from RH above 60% because the API and lactose monohydrate diluent can form stagnant spots in the dosing disc when residual moisture exceeds 2.5%. This is a specific failure mode on automatic tamping-pin machines; the correction is not higher compaction force but rather pre-drying of the milled blend.

Model addition ratio: 10.0% w/w Jiebai Granules API milled to D90 ≤ 150 µm, 83.5% w/w spray-dried lactose monohydrate, 4.0% w/w sodium starch glycolate, 2.0% w/w talc, and 0.5% w/w magnesium stearate. Lubrication is limited to 3 min after a 20 min V-blender mixing cycle at 12 rpm. The batch size for a 500 L V-blender is typically 250 kg, leaving 50% headspace for dilution and particle movement.

Downstream production starts with dry milling through a hammer mill fitted with a 0.8 mm screen; API is milled at a controlled feed rate to avoid frictional heat above 40°C. The milled API is then passed through a 0.5 mm screen before blending. Encapsulation is performed on a tamping-pin capsule filler at 3,000–5,000 capsules/h or a continuous dosing-disc machine for larger batches; in-process checks require fill weight precision of ± 3.0% and weight variation compliance with USP <905>. Terminal finished product types include size 0 hard gelatin or hydroxypropyl methylcellulose capsules in 30–100 unit HDPE bottles with a desiccant canister and induction seal.

Water-soluble oral powder for poultry and swine administration through automatic dosing pumps places a different set of constraints on the API than feed premix. The dissolved or suspended API is exposed to oxygen, chlorine, iron, and pH excursions in the drinking-water line; the formulation must therefore buffer or chelate the service water before the API degrades. A model batch using 20.0% w/w Jiebai Granules API, 79.0% w/w anhydrous glucose monohydrate, 0.5% w/w citric acid, and 0.5% w/w colloidal silicon dioxide disperses in water at 25°C within 120 s under 100 rpm stirring; with hard water above 300 mg/L calcium carbonate, sodium tripolyphosphate is added at 0.2% w/w to prevent precipitation. The powder is not designed for single-dose sachet accuracy alone; it must also remain chemically stable at a stock solution dilution of 1:100 over 24 h in galvanized or plastic header tanks.

Compliance reference for oral powder manufacture is the finished product marketing authorization; the powder itself is produced under EudraLex Volume 4 Part II, with stability data generated under VICH GL3. Uniformity of filled mass in single-dose sachets is assessed by Ph. Eur. 2.9.5 or USP <905>, while reconstitution performance is controlled by the product specification for dispersibility, final pH 4.0–6.0, and residual moisture ≤ 2.0%.

Model addition ratio: 20.0% w/w API, 79.0% w/w anhydrous glucose monohydrate, 0.5% w/w citric acid, 0.5% w/w colloidal silicon dioxide. If hard-water chelation is required, 0.2% w/w sodium tripolyphosphate is added and the glucose content is reduced to 78.8% w/w. A 100 kg batch therefore contains 20.0 kg API; a 500 g sachet delivers 100 g API.

Downstream production uses dry blending in a 500 L rotary mixer at 15 rpm for 15 min, followed by sachet filling under controlled humidity not exceeding 40% RH. The filling line is fitted with an in-check weigher rejecting sachets outside ± 2.0% of target gross mass. Primary packaging is a laminated film of low-density polyethylene, aluminium foil, and polyester; seal integrity is tested according to ASTM F88/F88M-21. Terminal finished product types include 500 g and 1 kg laminated sachets, 100 g dosing pump cartridges, and 5 kg bulk water-soluble packs for integrated poultry operations.

Tablet compression of a granule API is decided by the loss-on-drying and PSD, not by assay alone.

Compressed veterinary tablets require the API to flow under die-table conditions and to resist attrition during friability testing. The granulated starting material may deliver acceptable flow into a rotary press, but direct compression of untransformed Jiebai Granules API is rarely used when the angle of repose exceeds 40°. A compressed tablet formulation using 30.0% w/w API, 60.0% w/w microcrystalline cellulose PH102, 6.0% w/w crospovidone, 1.0% w/w colloidal silicon dioxide, and 3.0% w/w magnesium stearate produces a 200 mg tablet with 60 mg API. Compression force is mapped on a 16-station rotary press between 8 kN and 18 kN; hardness is held between 60 N and 90 N, friability is ≤ 1.0%, and disintegration is ≤ 15 min. A hardness above 90 N may delay disintegration; a hardness below 50 N raises chipping during film coating or blistering operations.

Compliance references are USP <701>, Ph. Eur. 2.9.1, USP <1216>, Ph. Eur. 2.9.7, and USP <905>. Tablet weight uniformity is assessed on 20 units for each of three compression force levels during the development batch; content uniformity follows USP <905> for low-dose products. The tablet core must be stored below 60% RH when crospovidone is used as the disintegrant because its wicking action is humidity-sensitive.

Model addition ratio: 30.0% w/w API, 60.0% w/w microcrystalline cellulose PH102, 6.0% w/w crospovidone, 1.0% w/w colloidal silicon dioxide, and 3.0% w/w magnesium stearate. In a 100 kg batch, the masses are 30.0 kg, 60.0 kg, 6.0 kg, 1.0 kg, and 3.0 kg. If the API particle size after milling is not controlled to D90 ≤ 150 µm, the magnesium stearate level must be reduced to 2.0% w/w and microcrystalline cellulose raised to 61.0% w/w to avoid delayed disintegration.

Downstream production begins with loss-on-drying measurement of the API granule. If LOD exceeds 2.0%, the API is pre-dried in a vacuum shelf dryer at 40–50°C for 4–6 h, then milled through a 0.8 mm screen. The API is blended with microcrystalline cellulose and crospovidone in a 500 L bin blender at 10 rpm for 20 min; magnesium stearate is added last and mixed for 3 min. Tableting is performed on a 16-station rotary press with turret speed 30–50 rpm and pre-compression force 2–4 kN. Terminal finished product types include 600 mg, 1 g, and 5 g veterinary tablets or large-animal oral boluses packed in aluminium blisters or HDPE bottles with desiccant.

If Terminal Moist-Heat Sterilization Is Applied to Aqueous Injections of Jiebai Granules

Aqueous injectable compounding is constrained by the requirement to dissolve or suspend the API in Water for Injections and to sterilize without generating sub-visible particulate matter. In terminal moist-heat sterilization at 121°C for 15 min, pH, oxygen headspace, and stopper extractables determine the degradation profile. A model aqueous solution at 5.0% w/v API is prepared with 0.9% w/v sodium chloride in Water for Injections; pH is adjusted to 5.5–6.5 before flushing with nitrogen to maintain dissolved oxygen below 0.5 mg/L. If forced degradation at 80°C for 72 h shows impurity increase above the specification threshold, the process is switched to aseptic filtration rather than terminal steam sterilization. Published data for this specific configuration is limited; therefore autoclave mapping must use product-specific worst-case loading in the validation batch.

Compliance references include Ph. Eur. 0520, USP <1>, USP <788>, ISO 14644-1 cleanroom class 5, and EU GMP Annex 1. Particulate matter limits for small-volume parenterals follow USP <788>: not more than 6,000 particles per container at ≥ 10 µm and not more than 600 particles per container at ≥ 25 µm. The vial, stopper, and seal system must be qualified for container closure integrity under USP <1207>.

Model addition ratio: 50.0 g API per litre, equivalent to 5.0% w/v; 9.0 g sodium chloride per litre for isotonicity; Water for Injections q.s. to 1.0 L. A 100 mL vial therefore contains 5.0 g API and 0.9 g sodium chloride. If the final product is a suspension injection, the API is wet-milled to a D90 ≤ 10 µm before sterile compounding; published data for this specific configuration is limited and must be supplemented with pilot-scale particle-size mapping under aseptic conditions.

Downstream production begins in a 500 L stirred stainless tank with Water for Injections at 30–40°C; the API is added under vacuum to avoid foam, and mixing is maintained at 150 rpm for 30 min. The solution is cooled to 20°C, passed through a 0.22 µm PVDF filter, and filled under nitrogen into depyrogenated Type I glass vials. Terminal moist-heat sterilization is performed in an air-overpressure autoclave at 121°C for 15 min only where forced degradation data confirm impurity control. Terminal finished product types include 50 mL and 100 mL single-dose glass vials with butyl rubber stoppers and flip-off seals.

For oral granule top-dress and direct-to-litter delivery, the finished product is a free-flowing granule intended to be sprinkled onto feed or administered directly with a dose cup. The critical processing point is not the API assay but the moisture barrier of the primary package. In a humidity challenge at 40°C / 75% RH for 30 days, a granule with residual moisture above 3.0% will cake and produce sub-visible compacted fragments that fail to disperse in the feed trough. A caked batch also loses dose uniformity because the end user cannot consistently scoop the intended mass; weight deviation from the labelled dose cup can exceed 10% when the granule flow is impaired. The granule route therefore uses a higher mannitol fraction than capsule or tablet routes to reduce hygroscopic surface area and maintain a Hausner ratio below 1.20.

Compliance reference for unit-dose sachets and bottles is USP <905> for mass uniformity and Ph. Eur. 2.9.5 for single-dose preparations. Stability testing follows VICH GL3, with accelerated conditions of 40°C / 75% RH for 6 months. The packaging is tested for seal integrity per ASTM F88/F88M-21 and for moisture vapour transmission rate below 0.1 g/m²/day for aluminium foil laminates. The release specification includes residual moisture ≤ 3.0%, loss on drying not more than 2.5%, and a particle-size distribution in which not more than 15% passes through a 125 µm sieve.

Model addition ratio: 50.0% w/w API, 43.0% w/w mannitol, 5.0% w/w povidone K30, 2.0% w/w crospovidone. In a 100 kg batch, these equal 50.0 kg, 43.0 kg, 5.0 kg, and 2.0 kg. A 100 g unit dose delivers 50 g API; a 250 g bottle delivers 125 g API. If the API assay is not compensated to the 100% potency basis, the batch must be adjusted according to the certificate of analysis.

Downstream production uses a high-shear granulator with impeller speed 300 rpm and chopper speed 1,500 rpm; the binder is purified water added at 8.0% w/w. Wet massing continues for 6 min, then the mass is transferred to a fluid-bed dryer with inlet air at 60°C and dried to residual moisture ≤ 3.0%. The dried granule is sized through a 1.0 mm screen and filled into HDPE bottles or aluminium unit-dose sachets under RH ≤ 40%. Terminal finished product types include 100 g and 250 g granule bottles, 5 kg bulk packs, and unit-dose sachets for feed top-dress.

Oral Drench Solutions: Co-Solvency, Filling Viscosity, and Stability Under Accelerated Shake Testing

Oral drench solutions for ruminants and pigs present a filling-line constraint: the maximum allowable viscosity at 20°C is typically 50 mPa·s for a volumetric piston filler to maintain a fill accuracy of ± 1.0%. A model oral solution using 10.0% w/v API, 20.0% v/v propylene glycol, 0.1% w/v sodium benzoate, and 0.05% w/v sodium saccharin in purified water is filtered through a 0.45 µm cartridge before filling. The co-solvent is not a solubilizer alone; it also shifts the freezing point of the drench product for storage in unheated farm cabinets. A storage chamber at -5°C must not produce precipitation or phase separation in the filled bottle; if separation is observed, the propylene glycol fraction is raised to 25.0% v/v and the API loading is re-validated for dose accuracy.

Compliance reference is the finished product marketing authorization and the relevant compendial general chapter for oral liquids, including Ph. Eur. 0520. Viscosity is measured by USP <911> or the corresponding European Pharmacopoeia method, with a target of ≤ 50 mPa·s at 20°C. Fill volume is checked by Ph. Eur. 2.9.5 for single-dose containers. Preservative efficacy testing follows Ph. Eur. 5.1.3 or USP <51> where the container is a multi-dose bottle.

Model addition ratio: 10.0 g API per 100 mL, 20.0 g propylene glycol per 100 mL, 0.1 g sodium benzoate per 100 mL, 0.05 g sodium saccharin per 100 mL, purified water q.s. to 100 mL. A 1 L batch contains 100.0 g API and 200.0 g propylene glycol. The final product is not terminally sterilized and is not intended for parenteral administration.

Downstream production uses a 500 L stainless mixing tank. Purified water is heated to 30–35°C; sodium benzoate is dissolved first, then propylene glycol is added, and the API is introduced under recirculation. Mixing continues at 200 rpm for 30 min, pH is adjusted to 4.5–6.0 with 0.1 N hydrochloric acid or 0.1 N sodium hydroxide, and the solution is passed through a 0.45 µm cartridge filter. Filling is performed on a volumetric piston line with inert gas blanketing if oxygen-sensitivity data require it. Terminal finished product types include 100 mL, 250 mL, and 1 L HDPE or PET drench bottles with calibrated dosing caps, and 5 L farm packs for automatic oral dosing guns.