At a core weight of 80 mg, a 5 mg carbimazole tablet corresponds to an API mass fraction of 6.25% w/w; a 10 mg strength in a 100 mg core corresponds to 10.0% w/w; and a 20 mg strength in a 140 mg core corresponds to 14.3% w/w. These mass fractions are maintained below the 20% w/w boundary at which low-dose direct compression blends frequently lose content uniformity under Ph. Eur. 2.9.40 unless geometric pre-blending is extended. Process capability on a rotary tablet press with 10 mm biconvex B-tooling and compression force of 5–12 kN is strongly influenced by the API particle size distribution; when the D₉₀ exceeds 250 µm, hopper segregation produces batch-to-batch content variability in the first and last 10% of machine output, and this has been observed on production-scale compression runs. The direct compression route therefore screens the API through a 500 µm stainless-steel sieve, performs a 1:5 w/w API-to-lactose monohydrate pre-blend for 10 min in a bin blender at 12 rpm, and then adds the remaining lactose, maize starch, pregelatinised starch, and colloidal silicon dioxide before final blending with magnesium stearate at 0.5–1.0% w/w for 3–5 min. The terminal finished product is an uncoated or film-coated immediate-release tablet. Occupational hygiene for carbimazole handling requires containment because the compound is an antithyroid agent; tablet press feed hoppers are placed inside a laminar downflow booth with a face velocity of 0.45 ± 0.05 m/s, and API dust retention losses are typically 0.1–0.5% w/w unless the exhaust filter is cleaned between batches. Compliance for this dosage form is anchored to Ph. Eur. 2.9.5 for uniformity of mass, Ph. Eur. 2.9.7 for friability, Ph. Eur. 2.9.1 for disintegration time, Ph. Eur. 5.1.4 for microbiological quality of non-sterile products, ICH Q3D(R2) for elemental impurities, and EU GMP Chapter 3 and Chapter 5 for cross-contamination control. The British Pharmacopoeia monograph for Carbimazole Tablets applies for assay and related substances, and the pharmacopoeial limits for any impurity above the reporting threshold are controlled in the API certificate of analysis. In-process controls include individual tablet mass at ±5%, hardness in the range 40–80 N, friability <1.0%, and disintegration time <15 min in water at 37°C.

Carbimazole strength	Core weight	API mass fraction	Uniformity test standard
5 mg	80 mg	6.25% w/w	Ph. Eur. 2.9.40
10 mg	100 mg	10.0% w/w	Ph. Eur. 2.9.40
20 mg	140 mg	14.3% w/w	Ph. Eur. 2.9.40

Why is wet granulation preferred when carbimazole content exceeds 14 mg per unit?

The wet granulation route is selected for the 20 mg tablet not because direct compression is impossible, but because the API mass fraction of 12.5–14.3% w/w in the dry granulate interacts with fine lactose and maize starch to produce a static-charged blend that segregates on high-speed tablet press feed frames. Carbimazole is practically insoluble in water, so binder selection is limited to aqueous polymer solutions without attempting to dissolve the API. Hypromellose binder solution is added at 2.0–3.0% w/w solids relative to the dry powder mass, and the granulation liquid amount is controlled between 15–25% w/w; endpoint is not time-based but torque-rise-based in the high-shear mixer. Dry mixing is performed at impeller speed 150–250 rpm and chopper speed 1500 rpm for 3 min; binder solution is sprayed over 2–3 min; wet massing continues for 90–180 s after the end of binder addition. The wet mass is milled through a 1.0–2.0 mm screen, dried in a fluid bed dryer at inlet air temperature 50–70°C to final granule moisture of 1.5–2.5% by loss on drying, and milled again through a 0.8–1.0 mm screen. The dried granulate is blended with sodium starch glycolate at 2.0–4.0% w/w and magnesium stearate at 0.5–1.0% w/w before compression on a rotary tablet press at 8–16 kN, yielding tablets with hardness 50–90 N. The terminal finished product is a film-coated 20 mg tablet. Dissolution is assessed with Ph. Eur. 2.9.3 paddle apparatus at 50 rpm in 900 mL of 0.1 M hydrochloric acid; immediate-release tablets of carbimazole typically require a Q of 75% at 45 min, but the compendial acceptance criterion is the controlling requirement where a monograph exists. Uniformity of dosage units is tested by Ph. Eur. 2.9.40, friability by Ph. Eur. 2.9.7, and residual moisture by loss on drying. Stability of the granulated intermediate is assessed under ICH Q1A(R2); if the granule water activity exceeds 0.6, the batch is routed to re-drying because moisture can accelerate thioamide degradation and reduce dissolution. The high-shear wet granulation route is more equipment-intensive than direct compression, but it reduces segregation risk in the tablet press feed frame compared with dry powder blending at equivalent API mass fraction. Batch size and granulator bowl load factor should not exceed 80% of bowl volume; overloading leads to uneven binder distribution and a wider granule size distribution.Hard gelatin capsule filling of carbimazole is not a widely recognised commercial monograph product; published data for this specific configuration is limited. A 5 mg strength in a size 3 capsule with 100 mg net fill weight corresponds to 5.0% w/w; a 10 mg strength in a 150 mg fill weight corresponds to 6.7% w/w; a 20 mg strength in a 250 mg fill weight corresponds to 8.0% w/w. Because each capsule contains less than 10 mg of API in most configurations, the filling process relies on geometric dilution rather than simple bin blending; the API is first premixed with lactose monohydrate at 1:5 w/w, then the remaining microcrystalline cellulose, maize starch, and colloidal silicon dioxide are added stepwise. A tamping-pin capsule filling machine with 1–3 tamping strokes and fill weight control at ±5% is used; the fill weight variation is checked by periodic balance check every 20 min. The capsule shells are hard gelatin or HPMC, and the finished product is an oral unit-dose capsule for patient-specific use or clinical trial blinding. Compliance for non-sterile capsule manufacture is anchored to Ph. Eur. 5.1.4, Ph. Eur. 2.9.40 and USP ⟨905⟩ for content uniformity, ICH Q3D(R2) for elemental impurities, and EU GMP Chapter 5 for production. Dissolution testing may be performed by Ph. Eur. 2.9.3 with a capsule sinker where a product-specific method is justified under ICH Q6A; no pharmacopoeial capsule monograph exists to provide a default acceptance criterion. Capsule filling at low API mass fraction can produce electrostatic retention of API on the filling machine dosing plate; addition of colloidal silicon dioxide at 0.2–0.5% w/w reduces this retention, but excess above 1.0% w/w can slow dissolution.

Granule sachet manufacturing for paediatric dose titration

Carbimazole oral granules are not an established monograph product in major pharmacopoeias; therefore published data for this specific configuration is limited. The following process is a platform low-dose granulation approach rather than a validated commercial granule dossier for carbimazole. A 2.5 mg dose in a 500 mg sachet gives an API mass fraction of 0.50% w/w; a 5 mg dose in 500 mg gives 1.00% w/w; a 10 mg dose in 1000 mg gives 1.00% w/w. These low fractions place the process in the segregation-sensitive region where dry powder blending alone is not sufficient; a 1:10 w/w API-to-lactose monohydrate pre-blend is prepared first, followed by step-wise dilution in a 100 L bin blender at 10–15 rpm for 10 min per dilution step. Top-spray fluid bed granulation is then used with hypromellose binder solution at 2.0–3.0% w/w solids, inlet air temperature 50–65°C, atomising pressure 1.5–2.0 bar, and spray rate adjusted to keep the bed moisture below 4.0% during granulation. Dried granules are sieved through a 1.0 mm sieve, and the terminal sachet is filled at ±5% fill weight variation with seal integrity testing per the packaging specification. Compliance is anchored to Ph. Eur. 2.9.40 for uniformity of dose units, Ph. Eur. 5.1.4 for microbial quality of non-sterile oral granules, ICH Q3D(R2) for elemental impurities, and ICH Q6A for specification justification. Dissolution of granules may be assessed after dispersion using Ph. Eur. 2.9.3; however, no product-specific dissolution criterion is currently available from a recognised carbimazole granule monograph. Handling a low-dose pediatric granule in a fluid bed process requires careful calibration of the binder spray nozzle because the API can be elutriated from the bed if the inlet air flow exceeds 2.0 m/s at the distributor plate; batch losses in early development have been traced to filter bag over-pulsing rather than granule fracture.

When injectable carbimazole is processed as a lyophilised powder for reconstitution

Carbimazole is practically insoluble in water, and no pharmacopoeial monograph for injectable carbimazole exists; consequently, the addition ratio for an aqueous injectable solution cannot be cited from a recognised standard. Published data for this specific configuration is limited. Development of an injectable product would need to address solubility through a co-solvent or complexation system, and the terminal finished product would be expected to be a lyophilised powder for solution or suspension for injection rather than a simple aqueous solution. Under EU GMP Annex 1 and ISO 14644-1:2015, the aseptic filling line for such a terminal product must be validated in Grade A/B zones with an airflow velocity of 0.36–0.54 m/s at the working position. Sterilising filtration of the bulk solution would require filter compatibility testing because the API may adsorb onto some hydrophobic membrane materials, and the process must be designed to maintain sterility without terminal sterilization if the thioamide function is heat-sensitive. Sterility testing would follow Ph. Eur. 2.6.1, bacterial endotoxin limits would be set using Ph. Eur. 2.6.14, sub-visible particulate matter would be controlled by Ph. Eur. 2.9.19, and container closure integrity would be verified under current EU GMP Annex 1 guidance. Because no monograph governs the finished injectable dosage form, the API concentration in any development batch would need to be defined from equilibrium solubility, forced degradation, and filter adsorption studies rather than from a pharmacopoeial addition ratio. The operational boundary is strict: contact with concentrated oxidizing agents should be avoided because the thioamide group is susceptible to oxidation, and prolonged exposure to acidic aqueous media may lead to hydrolysis of the carbamate function. No production-scale experience for carbimazole injectable is available in the public domain.