For multi-dose veterinary oral solutions, the concentrated Huoxiang Zhengqi extract is transferred into a stainless-steel mixing vessel fitted with a bottom-mounted high-shear impeller and a recirculation loop. The veterinary-grade API is typically supplied as a concentrated extract with reduced ethanol and higher solids than the human oral solution, which directly affects dilution ratio, preservative selection, and long-term physical stability. The extract is diluted with purified water meeting compendial water-for-preparations quality, with conductivity controlled below 1.3 µS/cm at 25°C and total organic carbon monitored to reduce bioburden carryover from the extraction process. pH adjustment with citric acid/sodium citrate buffer is maintained in the range of 4.0–5.5; outside this window the ionisable neolignan markers magnolol and honokiol may precipitate, and the volatile fraction can separate as a surface film. Preservative efficacy is not fixed by formula alone: sodium benzoate is evaluated between 0.05% and 0.15% w/v by challenge testing according to Ph. Eur. 5.1.3 or USP <51>, and the selected concentration is the minimum that meets the compendial acceptance criteria. Polysorbate 80 is incorporated as a solubiliser at the lowest concentration that maintains a visually clear single-phase liquid, typically below 1.0% w/w, because excess surfactant can produce foaming during high-speed filling and may alter the oral acceptance of the drench. The bulk solution is passed through a polypropylene depth filter with nominal retention of 0.45 µm before filling; filter load capacity is recorded because phenolic and polysaccharide residues from the herbal extract can prematurely block depth media. Type III amber glass or high-density polyethylene bottles with foil induction seals are preferred, as prolonged light exposure accelerates oxidation of perillaldehyde and causes colour shifts. Stability is assessed under accelerated storage at 40°C and 75% RH following VICH GL1, with assay of patchouli alcohol, perillaldehyde, magnolol, honokiol, and hesperidin by a validated HPLC method aligned to the Chinese Pharmacopoeia 2020 Huoxiang Zhengqi Oral Liquid monograph.

What Limits Direct Compression of the Extract in Veterinary Tablets?

Direct compression is constrained by the high dose, hygroscopicity, and poor compactability of the spray-dried extract. The neat extract has a low bulk density and a Carr index above 25% when measured according to Ph. Eur. 2.9.34 and 2.9.36, which causes die-fill variability on rotary tablet presses at production speeds above 30 rpm. The API is therefore processed by wet granulation in a jacketed high-shear granulator with impeller speed set between 200 rpm and 400 rpm and chopper speed between 1,000 rpm and 1,500 rpm; the granulating liquid is a dispersion of povidone K30 in ethanol/water, added at 8–15% w/w of the dry blend. The wet mass is discharged through a conical mill fitted with a 1.0 mm screen and dried in a fluid-bed dryer with inlet air temperature of 50–60°C and dew point below 8°C, with drying terminated when loss on drying is not more than 5.0% by Ph. Eur. 2.2.32. The dried granulate is blended with croscarmellose sodium as disintegrant and magnesium stearate at 0.5–1.0% w/w; blend time is limited to 3–5 min to avoid shear-induced over-lubrication. Compression is run on a rotary tablet press with precompression, targeting tablet hardness of 60–100 N, friability below 1.0% by Ph. Eur. 2.9.7, and disintegration not more than 30 min in water at 37°C by Ph. Eur. 2.9.1. Higher compression force improves hardness but delays disintegration because the plastic extract matrix deforms under pressure and closes the porous network that water needs for wicking. Film coating with an aqueous HPMC dispersion is used to mask the characteristic odour and to reduce light oxidation of marker compounds; the pan bed temperature is maintained at 38–42°C with inlet air at 60°C.

Capsule Dosator Fill Accuracy with Spray-Dried Extract

Spray-dried Huoxiang Zhengqi extract powder is cohesive and moisture-sensitive, which makes dosator-type capsule filling more sensitive to powder bed depth and fill pin compression ratio than free-flowing chemical powders. Colloidal silicon dioxide at 0.5–1.5% w/w and microcrystalline cellulose PH-102 are added in a bin blender at 10 rpm for 15 min to improve flow and increase bulk density; loading above 2.0% silicon dioxide reduces flow improvement and can cause dusting at the filling station. The encapsulation room is controlled below 40% relative humidity, because the extract powder reaches a sticky surface state above 5.0% moisture and begins to adhere to dosator pins, causing fill-weight drift outside the acceptance limit of ±5%. Hard gelatin capsule shells containing the extract have a documented failure mode: residual aldehyde components, particularly perillaldehyde, can crosslink gelatin and form a pellicle that delays dissolution. If the capsules fail dissolution at 45 min under USP <711> or Ph. Eur. 2.9.3, hydroxypropyl methylcellulose capsule shells are substituted, because HPMC does not undergo the same aldehyde-mediated crosslinking. After filling, capsules are sealed in polyvinyl chloride/polyvinylidene chloride or Aclar blisters with a desiccant; moisture ingress above 60% RH causes extract caking and capsule deformation. Release testing includes content uniformity by Ph. Eur. 2.9.40, assay of magnolol, honokiol, and hesperidin by HPLC using the Chinese Pharmacopoeia 2020 conditions, and microbial enumeration by Ph. Eur. 2.6.12 and 2.6.13.

At pen-side or feedyard dosing, dry powders are reconstituted immediately before use because the aqueous dispersion is not preserved against microbial growth. The powder is dry-mixed in a double-cone blender to a carrier blend in which the extract is pre-dispersed on maltodextrin, lactose monohydrate, or calcium lactate. Particle size is controlled by air-jet milling or screen milling so that the median particle size falls between 150 µm and 250 µm, measured by laser diffraction according to ISO 13320; finer fractions below 75 µm create dust and may slow wetting because the powder dissolves into a high-viscosity surface layer. Reconstitution is evaluated by adding the intended dose to 1 L of water at 20°C with stirring for 5 min; the acceptance criterion is a uniform suspension with no hard pack after 15 min and no retained particles on a 75 µm wet sieve. Water hardness and dissolved iron affect the appearance of the reconstituted suspension, because phenolic constituents can complex with ferric and ferrous ions and produce dark-coloured precipitates; non-chlorinated, sediment-free water is recommended for field administration. The dry powder is packaged in foil-lined heat-sealed sachets or moisture-barrier pouches, and the moisture permeation rate of the package is verified below 0.1 g/m²/day at 38°C and 90% RH to prevent caking during storage. If the product is intended for in-feed use, a larger particle size fraction may be selected, but this slows reconstitution and shifts the use toward the granulated form described below.

Wet Granulation of Volatile Oil Fractions into Soluble Granules

For soluble granules, the API is split into two processing streams because the volatile oil fraction is lost during prolonged wet mass drying. The aqueous extract solids are dissolved or dispersed in a binder solution and sprayed onto a dry blend of maltodextrin, sucrose or lactose, and pregelatinised starch in a top-spray fluid-bed granulator; the inlet air is set at 55–65°C, atomising air pressure at 2–3 bar, and the spray rate is adjusted to keep the bed temperature between 35°C and 40°C. Separately, the volatile oil fraction is adsorbed onto colloidal silicon dioxide or complexed with beta-cyclodextrin; this adsorbed fraction is added to the dried granulate in a tumble blender to avoid exposing the volatile markers to the highest temperature of the dryer. Drying is continued until loss on drying is not more than 3.0% by Ph. Eur. 2.2.32, and the resulting granule fraction between 200 µm and 500 µm is selected by screening. The dissolution rate in water at 25°C is measured with a paddle apparatus at 50 rpm; the granulated form should disperse completely within 5 min without leaving a hydrophobic oil film on the surface, which indicates incomplete adsorption of the volatile fraction. Residual ethanol from the granulating fluid is controlled under VICH GL18 Class 3 limits, and residual moisture is correlated with glass transition, because the amorphous spray-dried extract can plasticise and collapse if the package allows moisture ingress. Granules are filled into foil sachets under low humidity and sealed with an oxygen scavenger where long-term stability of perillaldehyde is required.

When Extract Solids Enter Medicated Premix Blending Lines

In feed mill premix production, the extract powder is seldom used as the sole ingredient; it is diluted into a mineral and vitamin carrier at an inclusion rate determined by the prescribed feed intake and the assayed marker content of the extract batch. Carrier selection is critical because the extract has a higher density and different particle morphology than ground corn cob or rice hull carriers; particle size ranges of 250–850 µm for the carrier reduce segregation, while finer carriers below 150 µm increase dust and adhesion to mixer surfaces. Mixing is performed in a ribbon mixer or double-shaft paddle mixer with a coefficient of variation for marker distribution below 10%, confirmed by sampling points distributed across the mixer and testing for magnolol, honokiol, and hesperidin by the Chinese Pharmacopoeia 2020 HPLC method; if the coefficient of variation exceeds 10%, the extract is pre-blended with a portion of the carrier before final mixing. Prolonged contact with trace minerals in the premix can accelerate oxidation of phenolic markers; ferrous sulfate and copper sulfate are particularly reactive with polyphenol-rich fractions, and contact is reduced by using chelated trace minerals or by keeping the extract in a separate additive compartment until final feed manufacture. Pelleting after premix addition exposes the volatile oil fraction to die temperatures of 70–85°C; post-pelleting liquid application of the heat-labile fraction is used where the mill has a liquid spray system, but this requires stability data for the marker compounds at the pellet surface. If the final feed is stored above 60% RH, extract particles absorb moisture and can form hard lumps that reduce homogeneity; dry, cool storage is therefore specified.

Injectable development uses the aqueous fraction after ethanol precipitation and membrane clarification, not the raw oral-liquid extract, because the presence of polysaccharides, proteins, and tannins in the unfractionated material creates an unacceptable particulate and pyrogen burden. The manufacturing sequence begins with cold ethanol precipitation at a temperature below 10°C, followed by high-speed tubular centrifugation at approximately 14,000 × g to remove denatured macromolecules. The clarified liquid is then processed by tangential-flow ultrafiltration through a polyethersulfone membrane with a nominal molecular weight cut-off of 10 kDa, which reduces endotoxin and high-molecular-weight colourants; endotoxin content after ultrafiltration is measured by Ph. Eur. 2.6.14, and the acceptance limit is derived from the intended dose per kg body weight and the route of administration rather than from a fixed compendial value. Sterile filtration through a 0.22 µm PVDF or polyethersulfone membrane is used because terminal autoclaving at 121°C degrades volatile marker compounds and shifts the colour of the solution; aseptic processing is therefore required. The filtered solution is filled into Type I borosilicate glass ampoules that have been depyrogenated at 250°C for 45 min; Type I glass limits sorption of lipophilic markers compared with polyolefin plastic containers. Published stability data for this specific injectable configuration are limited, so every batch is placed on a bracketed stability programme under VICH GL1 with assay of patchouli alcohol, perillaldehyde, magnolol, honokiol, and hesperidin, and the injection is not released until visible particles, pH, osmolality, and sterility meet the approved specification.