Aqueous dispersion coating of compressed tablet cores with EUDRATEC Fasteric is carried out in side-vented pans with inlet-air dehumidification sufficient to hold dew point below 10°C. EUDRATEC Fasteric is an aqueous acrylic enteric coating system based on methacrylic acid–ethyl acrylate copolymer; it is not the active pharmaceutical ingredient itself. The as-received system is supplied as a ready-to-dilute aqueous acrylic dispersion containing polymer, plasticizer and anti-tack component, so separate plasticizer addition is not required. Purified water is added under slow agitation to reduce solids content to 15–25% w/w. Dilution ratios above 1:1 lower bed humidity but extend coating time. Spraying is performed with a binary nozzle at atomising air pressure between 0.6 bar and 1.5 bar, while peristaltic spray rate and pan speed are balanced to hold product-bed temperature at 25–30°C and outlet relative humidity below 60%. For a 24-inch pan, pan speed is typically 8–14 rpm; for a 48-inch pan, 4–8 rpm. Coating weight gain on tablet cores is generally held at 5–10% w/w polymer solids relative to core mass; values below 4% w/w frequently produce gastric acid uptake above 10% after 2 h in 0.1 M HCl. After the final spray cycle, a curing step at 40°C for 1–2 h in the same pan or a tray dryer reduces residual moisture to below 2% w/w by Karl Fischer titration and stabilises film coalescence. Published production-scale batch records specific to EUDRATEC Fasteric are limited; the ranges given above are based on the aqueous methacrylic acid–ethyl acrylate copolymer dispersion class and manufacturer technical bulletins. The terminal dosage form is a delayed-release tablet for acid-labile active pharmaceutical ingredients such as proton-pump inhibitors, which resists 0.1 M HCl for 2 h and subsequently releases in pH 6.8 phosphate buffer within 45 min under USP 711 delayed-release conditions.

What Determines Acid Resistance at pH 1.2 Versus 5.5?

Below pH 5.5, the carboxylic acid groups on the methacrylic acid–ethyl acrylate copolymer remain protonated; the film presents low permeability to hydronium ions and protects the core active pharmaceutical ingredient from gastric fluid. At pH 1.2 in 0.1 M HCl, water uptake by the film is limited to 5–10% w/w after 2 h when pellet coating weight gain exceeds 20% w/w; tablet coatings at 8% w/w can show water uptake above 10% after 2 h because the applied film thickness is lower and surface defects are amplified relative to pellet geometry. At pH 6.8, ionization of carboxylate groups produces electrostatic repulsion, swelling and film rupture, which releases the active substance. The test method is USP 711 for delayed-release solid oral dosage forms: acid stage 2 h in 750 mL of 0.1 M HCl at 37 ± 0.5°C, followed by buffer stage at pH 6.8 and a dissolution criterion of Q = 80% at 45 min or 30 min depending on product registration. The pH threshold is not a single pKa value but the practical swelling point of the cured film; the fixed plasticizer ratio in EUDRATEC Fasteric shifts the effective threshold by 0.2–0.3 pH units compared with unplasticized copolymer films. Ionic strength in the dissolution medium above 0.2 M can reduce electrostatic repulsion and delay disintegration; therefore phosphate buffer concentration is controlled at 0.05 M in compendial tests. Product-specific disintegration is additionally checked with Ph. Eur. 2.9.3 using 0.1 M HCl for 2 h and then phosphate buffer pH 6.8; complete disintegration occurs within 10 min after buffer addition for robustly coated pellets.

In fluidised bed bottom-spray processing, neutral pellets of microcrystalline cellulose or sugar spheres are layered with an aqueous drug suspension containing hydroxypropyl methylcellulose or polyvinylpyrrolidone as binder. The layering step is run at product temperature 38–42°C until drug load reaches 20–50% w/w of the starting core mass. After drying to moisture below 1.5% w/w, the same Wurster column is used for enteric coating with EUDRATEC Fasteric diluted to 15–20% w/w solids. The Wurster partition gap is set to 15–25 mm, depending on batch size and pellet diameter; a gap below 10 mm restricts particle recirculation and raises spray loss, while a gap above 30 mm produces uneven film thickness at the outer annular bed. Superficial air velocity is held between 1.5 m/s and 2.5 m/s, with inlet air temperature at 50–60°C and outlet air temperature at 28–32°C. Spray rate is adjusted to maintain product temperature at 25–30°C. Coating efficiency below 90% leads to batch-to-batch acid uptake variability; filter-bag pressure drop is monitored because polymer fines blind the filter and reduce airflow after prolonged runs. A polymer weight gain of 15–25% w/w is used for multi-particulate systems because the surface area per unit mass is higher than tablets; the lower threshold of 12% w/w is rarely sufficient for robust acid resistance. Enteric-coated pellets are filled into hard gelatin or HPMC capsules, and the capsule product is tested by USP 711 with an acid-stage limit of not more than 10% drug release after 2 h followed by release in pH 6.8 buffer. The terminal product is a delayed-release capsule for oral administration.

When Compression Forces Fracture Enteric Films on MUPS

Compression of enteric-coated pellets into multi-unit pellet system tablets generates radial and shear stresses that can fracture the acrylic film at pellet-to-pellet contact points. The film thickness on a pellet coated to 20% w/w is typically 10–30 µm; flexural strain during compaction above 150 MPa frequently cracks the coating and produces premature drug release in 0.1 M HCl. MUPS tablet formulations therefore use microcrystalline cellulose and crospovidone at combined levels of 30–40% w/w as cushioning excipients, while magnesium stearate is limited to 0.5–1.0% w/w because hydrophobic surface coverage retards buffer penetration. Tablet press settings are held at compression forces that yield hardness values of 50–80 N; press speed above 40 rpm can increase elastic recovery and reduce film integrity. Pellet size also controls the failure point: pellets above 1.0 mm tend to generate larger contact areas and fracture more readily than pellets in the 0.5–0.8 mm range. After compression, tablets are checked for acid uptake by USP 711 acid stage; a loss of protection is observed if acid uptake exceeds 10% at 2 h. The process window is narrow because the same compression force that maintains tablet hardness also threatens pellet coating continuity. Pre-compression-coated pellets may be blended with extragranular EUDRATEC Fasteric-coated buffer pellets to separate the active pellets and reduce contact stress. The terminal product is an oral MUPS tablet with delayed-release properties comparable to the filled capsule but with reduced dose-flexibility risk for high-potency active ingredients.

Granule Layering, Drying, and Terminal Blending for Delayed-Release Sachets

Granules for oral sachet delivery are produced by spraying EUDRATEC Fasteric onto active-loaded sugar spheres in a rotor granulator or spouted bed. The dispersion is diluted to 15% w/w solids and sprayed at outlet air temperature 28–32°C; product temperature above 35°C leads to nozzle bead formation and film sticking. Coating weight gain for granules is kept at 10–20% w/w because granules below 400 µm have higher surface area and require sufficient film thickness for acid resistance. After coating, granules are dried in a fluid bed at 40°C until residual moisture by Karl Fischer titration is below 2% w/w; moisture above 3% w/w can soften the film during storage and raise acid uptake after 1 month at 40°C/75% RH. The dried granules are sieved to 300–800 µm, blended with mannitol, citric acid, silica and flavour in a tumbling blender, and filled into aluminium stick packs. The terminal product is a delayed-release oral granule for reconstitution or direct swallow, tested for acid resistance in 0.1 M HCl for 2 h and buffer release at pH 6.8 using USP 711 with sinkers. Because sachet moisture ingress through seams can plasticize the film, stick-pack seal integrity is checked by vacuum leak testing and headspace moisture by near-infrared spectroscopy.

For injectable administration, EUDRATEC Fasteric is not specified and no parenteral-grade monograph is established. The aqueous dispersion contains anionic acrylic polymer particles rather than a true solution; therefore aseptic filtration through 0.22 µm sterilising-grade membrane filters is not feasible, because the dispersed phase is retained and filter loading increases rapidly. Terminal sterilisation by moist heat at 121°C for 15 min would cause irreversible flocculation of the dispersion and phase separation, and the pH-dependent dissolution behaviour of methacrylic acid–ethyl acrylate copolymer creates a risk of uncontrolled precipitation below pH 5.5. The product is intended exclusively for oral solid dosage form coating after dilution and spraying; injectable active pharmaceutical ingredients should be formulated with parenteral-grade vehicles that meet sterility, endotoxin, and particulate limits of Ph. Eur. 2.9.19, USP 787 and USP 788. Unless the specific application is an oral dry suspension or granule, no terminal sterile filtration, autoclaving, or injectable spray-drying step should be attempted with this acrylic dispersion.