For solid oral dosage manufacture, tetraethylammonium bromide, CAS 71-91-0, molecular weight 210.16 g/mol, is first screened through a 0.5 mm sieve to eliminate storage agglomerates caused by hygroscopic uptake. A representative immediate-release tablet formulation uses the API at 45.0% w/w with microcrystalline cellulose at 33.5% w/w, pregelatinized starch at 10.0% w/w, crospovidone at 6.0% w/w, colloidal silicon dioxide at 0.5% w/w, and magnesium stearate at 1.0% w/w. The granulation vehicle is an aqueous solution of povidone K30 at 5.0% w/w; binder solution addition is set to 18–22% of the dry granulate mass. High-shear granulation is carried out in a top-drive mixer at impeller speed 150 rpm and chopper speed 1800 rpm. Impeller torque is maintained at 8–12 N·m during wet massing; this endpoint avoids over-wetting of the water-soluble salt, which can yield hard, poorly millable granules. The wet granules are dried in a fluidised bed at inlet temperature 55–65 °C until loss on drying is not more than 2.0% w/w by USP <731> or Ph. Eur. 2.2.32. Dried granules are passed through a 1.0 mm oscillating mill and blended in a 300 L bin blender at 10 rpm for 15 min. Compression is performed on a rotary press adjusted to give tablet hardness 80–120 N. Friability after 100 revolutions is not more than 0.8% by USP <1216>. Disintegration in purified water at 37±2 °C is set at not more than 15 min by USP <701>. Dissolution is conducted in 900 mL of 0.1 M hydrochloric acid using USP <711> Apparatus II at 50 rpm; the Q value is 80% at 30 min. The terminal tablet weight is 250 mg with an API content of 112.5 mg. Uniformity of dosage units is assessed by USP <905> with an acceptance value of not more than 15.0. Croscarmellose sodium is intentionally excluded from the formula because its pendant carboxylate groups can form poorly ionised complexes with the quaternary ammonium cation, reducing disintegration efficiency. Published data for this specific configuration is limited; therefore, the formulation is developed through a design-of-experiments matrix varying binder concentration and magnesium stearate level. At magnesium stearate levels above 1.0% w/w, dissolution may become hydrophobic film-limited even for a freely water-soluble active. The final blend is sampled at 10 points; blend uniformity RSD is set at not more than 5.0% for content. If RSD exceeds 5.0%, mixing is extended in 5-min increments. For a moisture-sensitive salt, packaging in aluminium-aluminium blisters is used when the sachet or bottle closure does not maintain headspace humidity below 40% RH.

What Limits Direct Compression of Tetraethylammonium Bromide on a Rotary Press?

Because unmilled salt has a Hausner ratio above 1.30 and a Carr index between 28 and 35, direct compression on a 45-station rotary press is incompatible with high-speed die filling at press speeds above 40 rpm. The hygroscopic surface of the quaternary ammonium bromide promotes sticking to steel tooling at punch tip pressures below 150 MPa. Magnesium stearate at 0.5% w/w may not eliminate picking; an increase to 1.0% w/w can slow dissolution through hydrophobic film formation. Roller compaction is therefore used to convert the blend into free-flowing granules before compression or encapsulation. A dry granulation formula consists of API 55.0% w/w, microcrystalline cellulose 25.0% w/w, lactose monohydrate 17.5% w/w, crospovidone 2.0% w/w, and sodium stearyl fumarate 0.5% w/w. The blend is passed through a roller compactor at roll pressure 4–5 MPa, roll speed 3–5 rpm, and gap 1.5 mm. Ribbon density is controlled between 1.05 and 1.20 g/cm³. The ribbon is milled through a 0.8 mm screen to produce granules with D50 180–250 µm. Hard gelatin capsules size 1 are filled on a dosator capsule machine at 30,000 capsules/h to a fill weight of 450 mg. Content uniformity is checked by USP <905> with acceptance value not more than 15.0. Dissolution is performed in 900 mL 0.1 M HCl at 50 rpm by USP <711>; Q 80% at 30 min. Roll pressure exceeding 6 MPa results in brittle ribbons that generate excess fines below 75 µm and reduce granule compressibility. Sodium stearyl fumarate is preferred over magnesium stearate where the quaternary ammonium cation shows long residence time on the dry blend, because the fumarate ester is less prone to form hydrophobic surface films on highly ionic crystals.

With a fluid-bed top-spray granulation line, the finished dose is produced as a single-dose granule for oral solution or suspension rather than a compressed solid. A representative charge contains API 10.0% w/w, sucrose 82.0% w/w, povidone K30 4.0% w/w, citric acid anhydrous 1.5% w/w, sodium saccharin 0.5% w/w, and a non-ionic flavour 2.0% w/w. The spray solution is povidone K30 at 8% w/w in purified water. In a top-spray fluid bed, inlet air temperature is held at 60–70 °C and product temperature at 35–40 °C. Atomising pressure is set at 1.5–2.0 bar and spray rate at 10–15 g/min per kg of dry charge. Drying is continued to loss on drying not more than 1.5% w/w by USP <731>. The dried granules are sieved through 500 µm; fines below 150 µm are limited to 10% w/w to maintain acceptable flow on auger-type sachet fillers. Sachets are filled to 5.0 g on a vertical form-fill-seal line; fill weight RSD is not more than 2.0%. Granule tests include loss on drying, particle size distribution by USP <786>, and microbial enumeration by USP <61> and USP <62>. A 5 g sachet dispersed in 50 mL water at 25 °C should wet and disperse within 60 s without forming gummy lumps. The pH of the resulting solution or suspension is measured by USP <791> and is specified at 5.0–6.5. Because the quaternary ammonium salt is highly water-soluble, wetting is not the main risk; segregation of the low-dose active in large sugar matrices is controlled by granulating the active with a portion of sucrose rather than dry blending the pure salt. Sachet packaging uses polyethylene-aluminium-paper laminate to keep moisture ingress below 0.5 g/m²/day at 40 °C and 75% RH.

Aqueous Injectable Presentation: Terminal Filtration and Package Integrity

After the active is dissolved in water for injection at 10 mg/mL, sodium chloride is added at 8.5 mg/mL as tonicity contributor; the solution pH is adjusted to 5.5–6.5 with 0.1 M sodium hydroxide or 0.1 M hydrochloric acid. Mixing is performed in a 100 L jacketed stainless steel vessel for 15 min. Pre-filtration uses a 0.45 µm polyethersulfone membrane; terminal filtration uses two 0.22 µm PVDF membranes in series. Nylon membranes are not selected because the quaternary ammonium cation can adsorb to negatively charged nylon surfaces. Filter integrity is tested before and after filling by bubble point and diffusive flow; a minimum bubble point for 0.22 µm PVDF in water is typically 3.2 bar. The solution is filled on a 12-head peristaltic aseptic filling line into 2 mL Type I glass vials at a fill volume of 2.0 mL and fill weight RSD not more than 2.0%. Terminal steam sterilisation is not applied unless thermal stability data for the specific formulation support it; the default process is aseptic filtration. pH is measured by USP <791>; osmolality by USP <785> is controlled between 285–310 mOsm/kg. Subvisible particulate matter is tested by USP <788>, visible particulates by USP <790>, sterility by USP <71>, and bacterial endotoxins by USP <85>. Container closure integrity is verified by USP <1207> using helium leak or dye ingress methods. Sterile filter validation uses Brevundimonas diminuta per ASTM F838-20. Residual elemental impurities are controlled by ICH Q3D; residual solvents, if any, are controlled by ICH Q3C. The bromide counterion is quantified by ion chromatography with conductivity detection to confirm salt stoichiometry in the finished injectable. The terminal product is a 2 mL single-dose vial. Aseptic holding time is limited to 12 h between final filtration and stoppering where no terminal sterilisation is applied.

Where long-term aqueous stability has not been demonstrated, lyophilized presentations are prepared with a pre-lyophilisation solution containing API 20 mg/mL, mannitol 40 mg/mL, trehalose dihydrate 20 mg/mL, and sodium citrate buffer 10 mM at pH 5.0. The solution is filled at 2.0 mL into 5 mL vials; fill volume RSD is not more than 1.0%. Shelf freezing proceeds at 0.5 °C/min to −45 °C and is held for 120 min. An annealing step at −10 °C for 60 min is introduced to crystallise mannitol and reduce the risk of cake collapse. Primary drying is performed at shelf temperature −20 °C and chamber pressure 100 mTorr for 24 h. Secondary drying is performed at 25 °C and 50 mTorr for 8 h. The resulting cake is white to off-white and intact. Moisture content by Karl Fischer is not more than 1.0% w/w by USP <921>. Reconstitution with 2.0 mL water for injection at 25 °C should yield a clear to slightly opalescent solution within 60 s. Subvisible particles after reconstitution are tested using USP <788>. If the cake collapses or moisture exceeds 1.0% w/w, the primary drying time is extended in 2-h increments and the chamber pressure is reduced by 10 mTorr intervals. Published data for this specific lyophilised configuration is limited; cycle design is verified by differential scanning calorimetry for glass transition and collapse temperature. The residual moisture limit is tightened to 0.8% w/w for vials intended for refrigerated storage.

When Continuous Twin-Screw Granulation Replaces Batch High-Shear Granulation for Scale-Up

In continuous manufacturing, the dry feed consists of API 42.0% w/w, mannitol 35.0% w/w, partially pregelatinized starch 12.0% w/w, crospovidone 6.0% w/w, and colloidal silicon dioxide 1.0% w/w. The binder is povidone K30 at 5.0% w/w in purified water. A co-rotating twin-screw granulator with screw diameter 16 mm and L/D ratio 40:1 operates at screw speed 300 rpm and powder feed rate 5.0 kg/h. Binder flow rate is set at 9.0 mL/min; barrel temperature is maintained below 40 °C to avoid thermal softening of the low-melting quaternary salt. Wet granules are dried in a continuous fluid-bed dryer with inlet temperature 65 °C and residence time 6 min. Dried granules are milled through 0.8 mm screen; bulk density is controlled between 0.48 and 0.58 g/mL. Tablets of 200 mg target weight are compressed to hardness 70–110 N, friability not more than 0.8%, disintegration not more than 12 min by USP <701>, and dissolution Q 80% at 30 min by USP <711>. Near-infrared process analytical technology monitors granule moisture in line with a set point of 1.0–1.8% w/w. If the moisture exceeds 2.0% w/w, powder feed rate is automatically reduced by 5% intervals until recovery. Anionic excipients with high carboxylate density are not used because they can interact with the quaternary ammonium cation and alter granule porosity. The continuous line reduces batch residence time but narrows the moisture operating window to approximately ±0.3% w/w. At feed rates above 8 kg/h, the barrel torque rises above 10 N·m per screw, at which point the binder distribution becomes non-uniform and tablet disintegration shifts beyond the 12-min limit.