A 40 mL/L dilution of the 2% w/v bromhexine HCl and 4.4% w/v menthol oral concentrate in a 60% w/w sucrose syrup containing 15% w/w sorbitol liquid yields a clear to slightly opalescent linctus with final bromhexine hydrochloride concentration of 0.08% w/v and menthol concentration of 0.176% w/v. This matrix supports a 10 mL unit dose containing 8 mg bromhexine HCl and 17.6 mg menthol when the concentrate is added as the sole source of both actives. Because L-menthol exhibits a melt transition at 41–43 °C and poor aqueous solubility, the concentrate must be pre-mixed with an equal volume of propylene glycol or warmed to 20–25 °C before introduction into the aqueous syrup to prevent local crystallisation and droplet entrapment in the bottom vortex. The syrup is adjusted to pH 3.0–3.5 with citric acid monohydrate and sodium citrate dihydrate to stabilise bromhexine hydrochloride in the ionised state. Mixing is carried out in a 316L stainless steel jacketed tank with bottom-entry propeller agitation at 350–500 rpm, followed by a rotor-stator homogeniser at 1500–2500 rpm for 15 min; the batch is then passed through a 10 µm inline filter and filled at 10–20 °C into amber glass Type III or HDPE bottles with child-resistant closures.

Compliance for the syrup is anchored to 21 CFR 211.110 in-process sampling, 21 CFR 211.113 microbial control, and ICH Q3C(R8) residual solvent limits where the concentrate contains ethanol or propylene glycol. Assay of bromhexine hydrochloride is performed by liquid chromatography per Ph.Eur. 2.2.29 using a C18 column and UV detection, while menthol is quantified by gas chromatography with flame-ionisation detection per Ph.Eur. 2.2.28; the menthol mass balance must account for headspace loss during transfer and filling. The final syrup contains 0.8 mg/mL bromhexine HCl and 1.76 mg/mL menthol. Terminal storage is specified at 15–25 °C, protected from light, with in-use stability evaluated after closure opening to confirm that menthol content does not fall below the lower assay limit because of volatilisation into the headspace.

What Processing Constraints Govern Chewable-Lozenge Granulation with the 4.4% Menthol Concentrate?

The 41–43 °C melt transition of L-menthol controls every drying and compression decision for chewable lozenges wet-massed with the concentrate. A 1200 mg chewable lozenge unit is formulated using 45% w/w D-mannitol, 25% w/w sorbitol powder, 15% w/w pregelatinized starch, 5% w/w crospovidone, and 0.4 mL concentrate per unit, which supplies 8 mg bromhexine HCl and 17.6 mg menthol. The wet massing step is performed in a 150 L planetary mixer at 120 rpm; the concentrate is pre-diluted 1:1 with propylene glycol to reduce localised menthol crystallisation and then poured into the dry powder over 3–4 min with the mixer running. Granulation end point is reached when the wet mass forms a compact mass without liquor seepage or visible syrup film on the bowl wall.

Tray drying is restricted to 30–35 °C with a chamber relative humidity of 30–40% until loss on drying is ≤1.5%; any dryer zone above 38 °C causes menthol sublimation and produces a drop in menthol assay and sticky granules that adhere to the punch face during compression. The dried granules are passed through a 1.0 mm oscillatory sieve and lubricated with 1% magnesium stearate by V-blender at 25 rpm for 5 min. Compression is performed on a 16-station rotary tablet press with B tooling at 40–55 kN compression force to achieve hardness 60–90 N and friability ≤1.0% per Ph.Eur. 2.9.7. Disintegration is tested per Ph.Eur. 2.9.1 with a limit of ≤15 min. The finished lozenges are sealed in cold-form aluminium/aluminium blister packs because menthol migrates through PVC/PVDC and can soften or embrittle conventional thermoformed films over long storage at 25 °C/60% RH.

When the Concentrate Replaces Separate Granulating Fluid in Immediate-Release Tablet Cores

In a 200 L top-driven high-shear granulator, the concentrate is metered as the sole granulating fluid into a preblend of 52% w/w lactose monohydrate, 25% w/w microcrystalline cellulose, 3% w/w croscarmellose sodium, and 20% w/w pregelatinized starch. The impeller speed is held at 120–150 rpm and the chopper at 1500 rpm; liquid addition rate is controlled at 0.4–0.6 kg/min for a 50 kg batch to prevent overwetting, which in this formulation produces a high-torque mass that cannot be discharged without scraper intervention. The amount of concentrate added is 400 mL per 1000 tablet cores, corresponding to 8 mg bromhexine HCl and 17.6 mg menthol per tablet. The wet mass is discharged through a 6 mm square-hole screen and transferred to a fluid-bed dryer.

Drying is executed with inlet air at 30–35 °C, product temperature at 22–26 °C, and inlet-air dew point below 5 °C; the endpoint is loss on drying ≤2.0%. A final screen at 0.8 mm is followed by lubrication with 0.5% w/w magnesium stearate in a bin blender at 12 rpm for 10 min. Compression on a rotary tablet press with D tooling at 10–15 kN force yields cores with hardness 50–80 N and disintegration ≤15 min per Ph.Eur. 2.9.1. Dissolution testing is conducted in 900 mL of 0.1 M hydrochloric acid at 37 °C and 50 rpm per USP <711>, with Q = 75% at 45 min as the release criterion. If a film coat is applied, the pan air temperature is kept below 35 °C to limit menthol loss through the coating suspension during 20–30 min of spray time; the cores are then sealed in cold-form aluminium/aluminium blister packs.

For stick-pack granules dosed at 8 mg bromhexine HCl per sachet, the concentrate is sprayed onto a fluidised powder bed of 70% w/w sucrose powder, 15% w/w maltodextrin, 5% w/w citric acid anhydrous, and 10% w/w pregelatinized starch in a top-spray fluid-bed granulator. The concentrate volume is 400 mL per 1000 sachets, providing 17.6 mg menthol per unit. Spray rate is set at 0.5–1.0 kg/min through a 2.8 mm nozzle, atomising air at 2.0–2.5 bar, inlet air temperature at 30–35 °C, product temperature at 23–27 °C, and filter shaking interval 30 s per 10 min to manage the partial wetting caused by menthol-laden droplets. After spraying, drying continues at the same inlet temperature until loss on drying is ≤2.0%; the granules are then sieved to retain not more than 10% on 710 µm and not more than 15% below 150 µm per Ph.Eur. 2.9.12.

The terminal stick-pack granule is filled into polyester/aluminium/low-density polyethylene laminate sachets on a vertical form-fill-seal machine with sealing temperature 150–170 °C and seal integrity verified by ASTM F88/F88M. Final sachet mass is adjusted to 4.5 g to provide acceptable dispersion in 150 mL of water at 20–25 °C within 60 s. Uniformity of mass is tested per Ph.Eur. 2.9.5; bromhexine hydrochloride assay is by Ph.Eur. 2.2.29 HPLC, menthol assay by Ph.Eur. 2.2.28 GC-FID, and residual solvent compliance is assessed under ICH Q3C(R8). The sachet product is stored below 25 °C and protected from moisture; menthol sublimation can generate headspace pressure inside the laminate and reduce assay if the seal barrier is interrupted, although published data for this specific laminate configuration is limited.

Hard Capsule Adsorption on Porous Carriers and Low-Relative-Humidity Filling

Adsorption of the concentrate onto a 50:10:40 mixture of microcrystalline cellulose, colloidal silicon dioxide, and pregelatinized starch converts the liquid into a free-flowing fill for two-piece hard capsules. For a 1000-capsule batch, 400 mL of concentrate is added to 800 g of carrier blend in a 300 L low-shear planetary mixer or V-blender fitted with an intensifier bar at 1500 rpm for 10–15 min. The liquid is added at 10–15 °C to maintain menthol in the dispersed state; if the carrier temperature rises above 25 °C, the menthol fraction can partition into the headspace and produce tacky agglomerates that bridge on the dosator pins. The resulting adsorbed powder is screened through a 0.8 mm sieve and lubricated with 0.5% magnesium stearate for 5 min.

Filling is performed on a dosator-type capsule machine at 60,000 capsules/h using size 1 hard gelatin or HPMC capsules under room relative humidity ≤40% to avoid moisture-induced stickiness and shell deformation. The capsule contents supply 8 mg bromhexine HCl and 17.6 mg menthol per unit. Uniformity of dosage units is verified per Ph.Eur. 2.9.40 or USP <905>; disintegration is tested at 37 °C in 900 mL of water per Ph.Eur. 2.9.1 with a limit of ≤15 min. The filled capsules are packaged in Aclar/PVC or cold-form aluminium blisters; menthol loss through standard PVC/PVDC is controlled by blister cavity design and by storage at 15–25 °C in sealed aluminium pouches. Dissolution testing for the capsule is carried out per USP <711> in 0.1 M hydrochloric acid with a Q = 75% at 45 min criterion, although published data for this specific menthol-containing bromhexine capsule formulation is limited and should be verified during scale-up.

Evaluating Parenteral Use and the Solvent-Menthol Exclusion Boundary

Parenteral manufacture requires an entirely different starting material from this 2% bromhexine HCl and 4.4% menthol oral concentrate. The menthol component and any ethanol or propylene glycol co-solvents found in oral concentrates are not established parenteral excipients, and the presence of 17.6 mg menthol per 8 mg bromhexine HCl dose creates injection-site irritation and haemolysis risk if formulated as an aqueous injectable. Injectable bromhexine hydrochloride is instead manufactured from a separate monograph-grade bromhexine HCl powder dissolved into Water for Injections under aseptic conditions; terminal sterilisation at 121 °C for 15 min is typical for a 2 mg/mL solution. Sterilisation method validation is conducted per Ph.Eur. 5.1.1, and water quality is specified under USP <1231>. The oral concentrate is therefore excluded from injectable downstream applications, and batch records must segregate liquid handling lines used for oral syrups from any injectable compounding area to prevent cross-contamination.