Rheological Constraints in High-Shear Wet Granulation of Amisulpride 400 mg Tablets

Amisulpride IP/BP/EP grade received as a crystalline powder is incorporated into 400 mg immediate-release tablets by high-shear wet granulation when direct compression is not feasible due to high drug loading and poor bulk flow. The IP/BP/EP grade API is released against the corresponding monograph for assay, related substances, loss on drying, and residual solvents, with additional particle size control for granulation consistency. Granulation is performed in a top-drive high-shear mixer with a 600 L bowl, three-blade impeller, and side chopper. Purified water containing povidone K30 at 5.0% w/w is sprayed at 2.0–3.0 kg/min until dry binder level reaches 2.5–3.0% w/w. Impeller speed is maintained at 180–220 rpm and chopper speed at 1500 rpm for 4–6 min. Endpoint is controlled by power consumption and wet mass consistency. Over-wet mass produces dense granules with D50 above 350 µm after drying, which increases tablet hardness but retards disintegration. The wet mass is transferred to a fluid bed dryer with inlet air temperature 60–70°C, product temperature 38–42°C, and drying continued until loss on drying per Ph. Eur. 2.2.32 reaches 2.0–3.0% w/w. Dried granules are milled through a 1.25 mm conidur screen and blended with croscarmellose sodium 3.0% w/w, microcrystalline cellulose 10.0% w/w, and magnesium stearate 0.5% w/w in a bin blender at 12 rpm for 15 min.

Compression onto a 27-station rotary tablet press with 13 mm round flat-faced bevel-edge B tooling uses pre-compression force 4–6 kN and main compression force 14–20 kN. Target tablet hardness is 120–160 N. Friability remains below 1.0% w/w when tested per Ph. Eur. 2.9.7. Disintegration time for uncoated tablets tested in water at 37°C per Ph. Eur. 2.9.1 generally falls below 15 min when granule porosity is retained. Dissolution is evaluated with Ph. Eur. 2.9.3 apparatus 2, 50 rpm, in 900 mL of 0.1 M hydrochloric acid at 37°C. When a marketing authorization requires an immediate-release criterion, the typical limit of not less than 80% dissolved at 30 min is applied. Over-granulation, binder migration, or overwetting must be controlled because these reduce pore diameter in the tablet matrix and shift release toward delayed dissolution. Tablets may be film coated with a hypromellose-based coating system to 3.0% w/w weight gain in a perforated pan coater at inlet air 60–70°C, pan speed 6–10 rpm, and spray rate 40–80 g/min. The terminal product is a 400 mg uncoated or film-coated tablet packaged in PVC/PVDC/aluminium blister with desiccant.

Direct compression of amisulpride at 50 mg and 100 mg dose strengths is applicable only when particle size reduction and ordered blending are used to overcome cohesive behavior. Micronized API with D90 not exceeding 20 µm is pre-blended with lactose monohydrate or microcrystalline cellulose through a 0.5 mm sieve at a 1:5 ratio. This pre-blend is loaded into a bin blender with additional excipients and mixed at 12 rpm for 20 min. Finished blend samples from 10 positions must show RSD below 3.0% before compression. Compression is performed on a 16-station rotary press with 8 mm round concave tooling, pre-compression force 2–4 kN, main compression force 6–10 kN, and turret speed 30–60 rpm. Compression force is adjusted to produce tablet hardness between 60 N and 80 N; higher force leads to extended disintegration. Content uniformity measured per Ph. Eur. 2.9.40 is the primary release criterion for the 50 mg strength because the active portion represents only 25% of a 200 mg core. Lubrication with magnesium stearate is limited to 0.5% w/w and 5 min because excessive mixing after lubrication reduces tensile strength through hydrophobic film coverage. Weight variation is monitored during the run; drift beyond ±5.0% of target weight indicates powder bridging or inconsistent forced feeder speed. The terminal product is a 50 mg or 100 mg immediate-release tablet, normally uncoated and packaged in aluminium blister.

What Limits Content Uniformity in Amisulpride 50 mg Capsule Blends?

Capsule filling of amisulpride at 50 mg dose strength is controlled by particle cohesion, electrostatic charging, and powder bed density. The formulation uses amisulpride IP/BP/EP grade micronized to D90 ≤ 20 µm, lactose monohydrate 80 M, maize starch, and colloidal silicon dioxide 0.5% w/w. Blending order follows geometric dilution of API with lactose in a 1:3 ratio, followed by additional excipients in a V-blender operating at 15 rpm for 20 min. Magnesium stearate is added at 0.5% w/w and blended for 3 min. Powder bed depth on a tamping pin capsule filler is maintained between 18 mm and 22 mm; excessive powder bed height increases fill weight variability. Hard gelatin capsules size 3 with a fill weight of 200 mg are used under controlled humidity to avoid shell embrittlement. HPMC capsule shells are selected for tropical packaging conditions to reduce cross-linking risk under 40°C/75% RH. Fill plugs are sampled for weight variation; acceptance per Ph. Eur. 2.9.5 for hard capsules applies. Content uniformity per Ph. Eur. 2.9.40 becomes critical because segregation of micronized API from larger lactose particles can raise acceptance value above 15. Dissolution of filled capsules is tested with Ph. Eur. 2.9.3 using the apparatus and rotation speed specified in the finished product dossier; a typical immediate-release criterion is not less than 80% released at 30 min in 0.1 M HCl. The terminal product is a hard shell capsule containing 50 mg amisulpride, packaged in PVC/PVDC/aluminium blister.

Granule Friability and Sieve Cut Retention in Sachet Filling

Amisulpride granules for oral suspension or sachet presentation are manufactured by top-spray fluid bed granulation to avoid excessive fines. A binder solution of hypromellose 3.0% w/w in purified water is sprayed onto a fluidized blend of amisulpride IP/BP/EP grade, mannitol, and pregelatinized starch. Inlet air temperature is set at 55–65°C, product temperature is maintained at 32–38°C, and spray rate is adjusted to keep bed humidity below 35%. Granules are dried to moisture content 1.5–2.5% w/w and then passed over 500 µm and 150 µm sieves. The retained fraction between 150 µm and 500 µm should exceed 85% w/w; fines below 75 µm are limited to 15% w/w to prevent dusting during vertical form-fill-seal filling. Packing on stick-pack machines uses auger dosing with fill weight control of ±5.0%; product contact parts are 316L stainless steel. The sachet laminate is polyester/aluminium/low-density polyethylene with moisture barrier below 0.5 g/m²/day at 38°C/90% RH. Sieve analysis is documented per Ph. Eur. 2.9.12. For granules intended for reconstitution, dispersibility is checked by stirring a unit dose in 50 mL water at 25°C for 60 s; no large aggregates should remain. Uniformity of content in single-dose sachets is evaluated by Ph. Eur. 2.9.40. The terminal product is a single-dose sachet containing the label dose of amisulpride, packaged for oral administration after dispersion or direct ingestion.

When Amisulpride Is Formulated as a Sterile Solution for Intravenous Infusion

Injectable amisulpride is prepared as a sterile aqueous solution in Water for Injections. The free base is dissolved under pH adjustment; if solubility is insufficient at neutral pH, dilute hydrochloric acid is added stepwise until a clear solution forms. The pH is measured per Ph. Eur. 2.2.3 and is maintained within the range validated for the supplied formulation; there is no universal target because the pH depends on buffer capacity and API concentration. Sodium chloride or mannitol is added to achieve an osmolality of 270–320 mOsm/kg measured by freezing point depression per Ph. Eur. 2.2.35. The bulk solution is filtered through 0.22 µm polyethersulfone membrane filters and filled into Type I glass vials washed and sterilized according to ISO 13408-1. Terminal sterilization by autoclaving at 121°C for 15 min may be used if the finished product specification demonstrates that related substances remain within acceptance limits; if pH-dependent degradation exceeds the threshold, aseptic filtration is mandated instead. Sterility is tested by Ph. Eur. 2.6.1. Bacterial endotoxin limits are calculated from the maximum bolus dose per kilogram body weight using Ph. Eur. 2.6.14. Sub-visible particulate matter is controlled by light obscuration per Ph. Eur. 2.9.19; for small-volume parenterals the general limits are not more than 6000 particles per container at ≥10 µm and not more than 600 particles per container at ≥25 µm. The terminal product is a single-dose injection for intravenous infusion after dilution with 0.9% w/v sodium chloride or 5% w/v glucose solution.

Extemporaneous preparation of amisulpride oral liquid from bulk IP/BP/EP grade API is performed in hospital pharmacy when no commercial oral solution is available. The crystalline powder is dissolved in purified water with pH adjustment using citric acid or hydrochloric acid to a final pH below 5.5 because the solubility of the free base increases under acidic conditions. A preservative system containing methyl parahydroxybenzoate 0.1% w/w and propyl parahydroxybenzoate 0.02% w/w is incorporated when the preparation is stored for multiple doses. The solution is packaged in amber glass bottles and stored at 2–8°C; published stability data for this specific configuration is limited, so a beyond-use date not exceeding 90 days is assigned based on conservative pharmaceutical judgment. Delivered dose uniformity is checked periodically by HPLC with reference to Ph. Eur. 2.2.29. If the API is not fully dissolved, a suspension formulation using xanthan gum 0.3% w/w as suspending agent is prepared, but resuspendability must be demonstrated by vigorous shaking for 30 s. This product is intended for oral administration only and must not be injected due to the absence of sterility and pyrogen control. The terminal product is a 1 mg/mL or similar strength oral liquid labeled with the exact concentration and storage instruction.