Gastric Acid Inactivation Limits the Oral Tablet/Capsule Design Window

Native recombinant human trypsin is irreversibly denatured when exposed to gastric fluid pH values below 3.0; therefore oral tablet and capsule development begins with an enteric polymer barrier rather than a conventional immediate-release matrix. The core is manufactured by dry granulation because aqueous wet granulation initiates autolysis within 2 h at neutral pH in the absence of calcium chloride. Roller compaction with a 1.0 mm milling screen produces granules with a bulk density of 0.55 to 0.70 g/mL; direct compression of the API with microcrystalline cellulose and lactose monohydrate is acceptable only when the API content per unit exceeds 10,000 USP Trypsin Units and the powder blend is held at ≤30% RH. The compressed core is coated with a methacrylic acid-ethyl acrylate copolymer dispersion such as Eudragit L30 D-55 in a Wurster fluid bed coater; coating weight gain is controlled to 8%–15% of core mass and plasticised with triethyl citrate at 10%–20% w/w of dry polymer. The coating layer dissolves only above pH 5.5, which prevents enzyme release in the stomach. Dissolution is tested using USP <711> with a two-stage method: 0.1 M hydrochloric acid for 2 h with not more than 10% activity release, then pH 6.8 phosphate buffer with not less than 75% release at 45 min. Tablet hardness is maintained at 50 to 80 N to avoid coating fractures during pan movement. Lubricant levels of magnesium stearate are kept at 0.5%–1.0% because higher amounts create a hydrophobic film that interferes with aqueous coating adhesion. The final dosage form is an enteric-coated tablet or capsule containing acid-resistant granules. Activity is confirmed by BAEE hydrolysis at 253 nm using the USP monograph method, not by protein absorbance alone.

Single-dose granule formats filled into stick-pack or sachet lines use fluid bed drug layering instead of roller compaction because the terminal product must disperse rapidly in cold water. Recombinant human trypsin is dissolved at pH 3.0 to 3.5 with calcium chloride 1 to 5 mM; this short-term acidic vehicle suppresses autolysis during the spray period. The solution is applied onto microcrystalline cellulose spheres of 500–710 µm in a bottom-spray fluid bed processor with an inlet air dew point below −20°C. Drug load is limited to 5%–20% w/w of the starting sphere mass to prevent incomplete dissolution at the target pH 6.8. A hydroxypropyl methylcellulose subcoat of 2%–4% weight gain separates the enzyme layer from the enteric polymer; direct contact with acidic copolymer dispersion can lower the microdomain pH below 3.0 and reduce activity during storage. Enteric coating with Eudragit L100-55 or an equivalent Ph. Eur. methacrylic acid copolymer dispersion is applied to 10%–15% weight gain. Final drying at 35°C to 40°C inlet air continues until loss on drying is NMT 2.0% by USP <921> Method Ia. The terminal product is a granule-filled stick-pack that is dispersed in water immediately before dosing. The dispersed granules should not be held in water for more than 20 min because the enteric film begins swelling above pH 6.0. Dissolution testing for the sachet product follows USP <711> on the dispersed granule fraction, not on an intact tablet; the acceptance criteria are the same two-stage acid-neutral profile. Filling is performed at ≤25°C and ≤30% RH to avoid static charge and moisture uptake.

What Reconstitution Parameters Govern Proteolytic Activity Recovery in Lyophilized Injectables?

For a lyophilized injectable, the primary loss mechanisms shift from acid denaturation to ice-surface denaturation and post-reconstitution autolysis. The formulation buffer is prepared at pH 6.5 to 7.5 with 10 mM histidine or phosphate and includes calcium chloride 1 to 5 mM because calcium binding stabilises the native trypsin fold. Sucrose or trehalose is added at a 2:1 to 5:1 stabiliser-to-protein mass ratio; published data for an exact recombinant human trypsin configuration is limited, and this range is evaluated by freeze-thaw stress. Mannitol at 40 to 50 mg/mL provides crystalline bulk that shortens primary drying. The bulk solution is passed through a 0.22 µm PVDF membrane; nylon membranes are excluded because non-specific protein adsorption removes activity. Filling under EU GMP Annex 1 grade A conditions is followed by freezing on a lyophilizer shelf at −40°C with a ramp of 0.5°C/min. Primary drying is held below the collapse temperature of approximately −30°C, controlled by comparative pressure measurement with a Pirani gauge and capacitance manometer. Secondary drying at 20°C to 25°C for 4 to 6 h reduces residual moisture to <1.0% by Karl Fischer. The terminal product is a sterile lyophilized cake reconstituted with water for injection to an activity of 50,000 to 100,000 USP Trypsin Units per vial. After reconstitution, the solution is held at 2–8°C and used within 2 h because calcium dilution restores autolytic potential. Sterility is confirmed by USP <71>; bacterial endotoxin is controlled per USP <85> with a route-specific K/M calculation. Subvisible particulate matter is monitored by USP <787> and USP <788>. Container closure integrity is verified by dye ingress or vacuum decay per USP <1207>.

When a ready-to-inject liquid is selected instead of a lyophilized cake, the formulation must maintain proteolytic activity in a homogeneous low-particulate solution over a defined cold-chain period. Trypsin in aqueous solution exhibits measurable autolysis at neutral pH; the rate is reduced by including calcium chloride 5 mM and 0.01% polysorbate 20. A pH of 6.5 to 7.5 is selected with 10 mM phosphate buffer. Acidic vehicles below pH 4.0 are incompatible because they cause irreversible unfolding; alkaline conditions above pH 8.0 accelerate self-cleavage. The solution is sterile filtered through a 0.2 µm PVDF or PES membrane with a borosilicate glass prefilter. Filter validation includes a product-specific bacterial retention test and an adsorption study because activity can fall by 10%–20% after the first 200 mL filter pass in small-scale runs. The terminal product is filled in Type I borosilicate glass vials per USP <660> with elastomeric closures per USP <381>. Headspace oxygen is displaced with nitrogen to residual oxygen below 1.0%. Filling is performed with low-shear ceramic rotary piston pumps; peristaltic tubing with high pulsation is avoided because mechanical stress produces soluble aggregates. Terminal sterilisation by moist heat is not applicable because activity falls at 60°C within 10 min; aseptic filtration remains the sterilizing-grade step. Storage is limited to 2–8°C protected from light. Soluble aggregate is controlled by size-exclusion HPLC with a limit of not more than 5.0% high-molecular-weight species. Silicone oil-coated prefilled syringes are not recommended because silicone oil droplets nucleate protein aggregation and subvisible particle formation.

Co-Formulation with Chymotrypsin or Bromelain in Fixed-Dose Oral Solids

Fixed-dose oral solids containing recombinant human trypsin and a second protease are manufactured by separate granulation trains because each enzyme has different moisture and pH lability. Recombinant human trypsin is dry granulated by roller compaction at a roll force of 15–25 kN and milled through a 1.0 mm screen. Chymotrypsin is processed similarly but is typically more stable in acid; bromelain is granulated separately with anhydrous calcium hydrogen phosphate and kept at ≤25°C because it is moisture-sensitive. The two or three granule phases are blended by mass according to an activity ratio expressed in FIP or USP units; exact mass ratios are not interchangeable because enzyme specific activity varies between raw material batches and published data for a specific recombinant human trypsin combination is limited. The final blend is compressed at 15%–30% relative humidity and coated with an enteric polymer at 10%–15% weight gain. Without this coat, gastric acid inactivates both trypsin and chymotrypsin within 30 min. Dissolution testing under USP <711> must be performed in a two-stage acid-neutral configuration and both enzyme activities must be assayed by BAEE or AAP-type chromogenic substrate, not by total protein absorbance at 280 nm. Content uniformity is evaluated for each enzyme separately per USP <905>. The terminal product is an enteric-coated fixed-dose tablet packaged in aluminium-aluminium blisters with a desiccant; total moisture is maintained below 3.0% by USP <921>. This dosage form imposes the most complex analytical release panel because each enzyme requires its own activity assay and impurity profile.

When Modified-Release Behaviour Demands Multiparticulate Pellets Instead of Monolithic Tablets

Multiparticulate pellets are selected when the oral dose exceeds 10,000 USP Trypsin Units or when a monolithic enteric-coated tablet risks dose dumping due to film defects. Pellet cores are produced by low-shear extrusion-spheronisation using a basket extruder fitted with a 0.8 mm screen and a spheronizer operated at 400–800 rpm. The wet mass contains microcrystalline cellulose, lactose monohydrate, and recombinant human trypsin at 5%–15% w/w. Water addition is controlled so that the wet mass temperature stays below 20°C; high local shear in the extruder can raise the wet mass above 35°C and reduce activity. Spheronized pellets with a diameter of 850–1000 µm are dried in a fluid bed dryer at 35°C to 40°C until moisture is <2.0%. Enteric coating is applied to 12%–18% weight gain; pellet films must be thicker than tablet films because curvature and surface defects reduce gastric resistance. The terminal product is a hard gelatin or HPMC capsule filled with enteric-coated pellets on a capsule filling machine with vacuum dosing and metal-check weighing. Dissolution is tested by USP <711> apparatus 1 or 2 using the delayed-release two-stage method. Capsule shells with moisture above 13% are rejected because water migration can cause polymer film sticking and activity loss. Pellets are packaged in aluminium foil blisters with desiccant and stored at ≤25°C. This format has operational boundaries: pellet coating time is longer than tablet coating and requires separate gun calibration; in-process agglomeration in the spheronizer is controlled by adjusting water feed rate and binder concentration.