For tablet and capsule production, aged or spray-dried Dihuang powder is not a free-flowing direct-compression substance at relative humidity above 60% because it contains residual oligosaccharides, mineral ash, and water-soluble iridoid glycosides such as catalpol. A direct-compression formulation operating at 20–35% w/w Dihuang powder typically uses 40–55% w/w silicified microcrystalline cellulose, 2–5% w/w crospovidone, 1.0–1.5% w/w colloidal silicon dioxide, and 0.5–1.0% w/w magnesium stearate. Blending is performed in a 300 L V-blender at 15 rpm for 15 min after the API has been passed through a 500 µm stainless steel mesh; the final blend is rejected if the catalpol assay relative standard deviation across 10 sampling points exceeds 3.0%. Compression on a 27-station rotary press with 12 mm round punches uses a pre-compression force of 2–4 kN and a main compression force of 10–18 kN, with target tablet hardness of 80–120 N. Friability is tested according to USP <1216> and should remain ≤1.0% w/w, while disintegration is determined in water at 37±2°C by USP <701> and should complete within 30 min for uncoated tablets. Dissolution testing, where required, is run with USP <711> Apparatus 2 at 50 rpm in 900 mL degassed water at 37±0.5°C, with sampling at 15, 30, 45, and 60 min to report catalpol release as percentage of label claim. For capsules, the same API is dry-granulated instead of direct-blended when fill weight exceeds 400 mg or when the Dihuang fraction exceeds 30% w/w; roller compaction is run with roll force 6–10 kN/cm and ribbon density 1.1–1.3 g/cm³, followed by screening through a 0.8 mm sieve, then filled into size 0 or size 1 HPMC capsules. Content uniformity for both tablets and capsules is assessed by USP <905> with acceptance value ≤15 unless the relevant finished product monograph imposes a tighter limit. The terminal products are individual-animal oral dosage forms used where feed-route dosing cannot guarantee discrete intake, and they are packed in PVC/aluminum blister or HDPE bottles with desiccant because residual moisture above 5.0% w/w accelerates caking and discoloration during storage at 40°C/75% RH.

How Does Dihuang Powder Behave in a Multi-Ingredient Swine Feed Premix?

In multi-ingredient swine feed premix operations, the critical quality attribute shifts from tablet hardness to blend uniformity under low API inclusion and high carrier volume. Dihuang powder is not added directly to finished feed because the cohesive botanical particles segregate and adhere to mixer surfaces; it is first converted into an intermediate concentrate by geometric dilution. A standard premix blend uses ground limestone or rice hull meal as carrier at 45–60% w/w of the total premix, with Dihuang powder adjusted to 5–20% w/w active fraction. Each dilution step is 1:10 by mass, mixed for 5–10 min in a 100 kg paddle or ribbon blender before the next addition. The final premix is mixed in a ribbon blender at 25–35 rpm for 12–20 min with a fill factor of 60–80% of gross volume. Homogeneity is acceptable when assay of catalpol in 10 sampling points yields relative standard deviation ≤5.0%. If the premix is intended for medicated feed use, the manufacturing facility must operate under 21 CFR 225 current good manufacturing practice and the formula must conform to the authorized application in the respective jurisdiction. Carriers containing more than 0.5% w/w free moisture should be pre-dried at 60°C until moisture is ≤0.5% w/w because the extract powder absorbs water and can form agglomerates around mixer blades. The terminal product is a free-flowing dry premix packed in 25 kg valve bags with an inner polyethylene liner, labeled with the exact marker concentration and a storage condition of ≤25°C and ≤60% relative humidity. Batch-to-batch variance of root-derived marker content requires normalization of the premix fill weight against the certificate of analysis before release; published data for this specific low-dose dilution configuration is limited.

Fluid-Bed Granulation of Dihuang Powder for Poultry Drinking-Water Dispersibility

To prepare a drinking-water dispersible granule, Dihuang powder is granulated in a top-spray fluid bed using an aqueous binder solution of povidone K30 at 3–5% w/w of dry solids; the binder solution is sprayed at 60–120 g/min for a 5 kg batch. Inlet air is maintained at 60–70°C and product temperature at 35–42°C, because higher inlet air temperatures darken the extract and may reduce water-soluble marker recovery; the process window is controlled within ±5°C. Sodium lauryl sulfate at 0.1–0.3% w/w is added to the dry blend before granulation to lower surface tension, and citric acid at 1–2% w/w is included when hard water above 250 ppm calcium carbonate equivalent is expected. The finished granule D50 is controlled at 250–600 µm by nozzle aperture and spray rate. Dispersion is tested by adding 5 g of granules to 1 L of water at 25°C while stirring at 150 rpm; the dispersion must pass through a 180 µm sieve within 3 min with undispersed residue ≤1.0% w/w. Loss on drying is controlled by Ph. Eur. 2.2.32 at ≤5.0% w/w, and the product is packed in HDPE jars with silica gel desiccant. The terminal product is a measured-volume granule for poultry or swine drinking-water medicators, stored at ≤25°C and ≤60% relative humidity. If the granule will be used in water lines with a 1:128 proportioner, the formulation must be tested at the maximum stock solution concentration to confirm no precipitation or viscosity increase after 24 h.

Unlike oral solid dosage forms, injection-grade application of Dihuang powder cannot rely on simple dissolution of the spray-dried API because the powder carries insoluble plant cell wall fragments, high-molecular-weight polysaccharides, and potential endotoxin load from root material. The starting powder is dispersed in Water for Injections at 10–20% w/v, heated to 50–60°C for 30 min, and clarified by continuous centrifugation at 10,000×g. The supernatant is then processed by tangential-flow ultrafiltration with a 10 kDa molecular weight cut-off membrane to reduce high-molecular-weight polysaccharides and endotoxin aggregates. The permeate is concentrated, pH-adjusted to 6.0–7.5 with dilute hydrochloric acid or sodium hydroxide, and adjusted to isotonicity with sodium chloride 0.9% w/v or mannitol 5.0% w/v. Terminal sterilization by autoclaving at 121°C for 15 min is permitted only after the finished batch demonstrates marker recovery of at least 95% of the pre-sterilization assay; otherwise, aseptic filtration through a 0.22 µm PVDF membrane is used. The solution is filled under nitrogen into 10 mL or 50 mL amber borosilicate vials. Release testing includes sterility per USP <71>, bacterial endotoxins per USP <85> using the K/M-derived limit, particulate matter per USP <788>, visible particles, pH per Ph. Eur. 2.2.3, and color intensity. The terminal product is a sterile veterinary injection for intravenous or intramuscular administration only when the specific product has a valid marketing authorization.

When the Powder Is Reconstituted as an Oral Drench, What Preservative and Viscosity Limits Apply?

For oral drench solutions, preservation and suspendability present different challenges because the route is non-sterile but the product may be stored after opening in farm conditions. Dihuang powder is dispersed in purified water at 5–15% w/v, and a suspending agent such as xanthan gum at 0.1–0.3% w/v is hydrated before API addition if the formulation retains insoluble components. Preservation uses sodium benzoate 0.1% w/v plus potassium sorbate 0.1% w/v, with the finished pH adjusted to 4.5–6.0 to keep benzoic acid in its active undissociated form while avoiding extreme acid conditions that may promote hydrolysis of iridoid glycosides. Homogenization in a rotor-stator mixer at 5000 rpm for 15 min reduces particle size; viscosity is controlled at 50–200 mPa·s at 25°C using a Brookfield RV spindle 2 at 50 rpm because higher viscosity may cause variable drench gun delivery. Microbiological quality is tested according to Ph. Eur. 5.1.4 category 3B or equivalent, with acceptance criteria of total aerobic microbial count ≤100 CFU/mL, total combined yeasts and moulds ≤10 CFU/mL, and absence of Escherichia coli in 1 mL. Photostability is evaluated under ICH Q1B to set label storage because sorbate-preserved botanical liquids may darken over time. The terminal product is a ready-to-administer oral drench packaged in 1 L or 5 L HDPE containers with a draw-off cap, and it is labeled for non-sterile oral use only. Published data for this specific configuration is limited, so preservative efficacy testing according to Ph. Eur. 5.1.3 or USP <51> is required for shelf-life assignment.

When direct oral powders are packaged as unit-dose sachets, the carrier dry blend must transform the hygroscopic extract powder into a free-flowing mixture without granulation. Dihuang powder is dry-blended with glucose monohydrate or maltodextrin at a ratio of 1:3 to 1:9 by mass to achieve a sachet fill weight of 5–20 g, depending on the required dose. Fumed silica at 0.5–1.0% w/w and magnesium stearate at 0.5% w/w are added to control interparticle cohesion. The blend is filled into foil-laminate sachets under controlled room conditions of ≤35% relative humidity and sealed at 140–160°C. Loss on drying is limited to ≤6.0% w/w by Ph. Eur. 2.2.32, and the final powder must pass through a 500 µm sieve to prevent feed refusal caused by coarse particles. Stability screening is run at 40°C/75% RH for 6 months as specified in ICH Q1A, although published data for this exact Dihuang powder configuration is limited. The terminal product is a non-sterile oral powder for top-dress application in cattle, horses, pigs, or companion animals, packed in unit-dose sachets within a secondary HDPE carton containing desiccant.