Dry dispersion of tenofovir alafenamide fumarate into directly compressible tablet matrices is executed as a staged low-shear blend followed by high-shear milling, not as a single direct addition to the final blender. When the target uncoated core mass is 450–650 mg and the nominal TAF fumarate dose is 10 mg or 25 mg, the drug substance is present at 1.8%–5.0% w/w, a range that creates segregation risk under free-fall transfer. The TAF fumarate and a portion of mannitol or anhydrous dibasic calcium phosphate are pre-blended in a 100 L intermediate bulk container for 10 minutes, then passed through a Comil U5 conical mill with a 0.039 in. round-hole screen at 1,200 rpm. The remainder of the directly compressible filler, crospovidone 5% w/w, pregelatinized starch 10% w/w, and croscarmellose sodium 3% w/w are added, followed by final blending for 15 minutes at 12 rpm in a bin blender equipped with an intensifier bar. Production-scale batches show that TAF fumarate can segregate at blend transfers if the API pre-blend is added directly to the final bin blender without an intensifier bar; stratified samples from 1,000 kg scale batches then show relative standard deviation values above 6%, whereas the same formulations blended with a 100 L pre-blend and intensifier-bar route remain at RSD ≤ 5.0%.

Blend uniformity testing is performed under 21 CFR 211.110(a) using stratified sampling at the top, middle, and bottom of the blender at full speed and at 10 rpm deceleration; acceptance is RSD ≤ 5.0% for TAF fumarate content by validated HPLC. Lubrication with magnesium stearate at 0.5%–1.0% w/w for 3–5 minutes is used, and over-lubrication beyond 8 minutes is controlled because it reduces tablet breaking force and prolongs disintegration. Compression is performed on a Korsch XL 400 rotary tablet press with 43 B-tooling stations at main compression force 12–25 kN and precompression 3–5 kN; turret speed is 20–40 rpm. Tablet hardness is held at 80–120 N, friability is ≤0.8% per USP <1216>, and ejection force is maintained below 150 N. Release testing includes USP <711> Apparatus 2 dissolution in 900 mL of 0.01 N HCl at 37°C ± 0.5°C with paddle speed 75 rpm, USP <905> uniformity of dosage units with acceptance value ≤ 15.0, ICH Q3B(R2) degradation product thresholds scaled to a 25 mg daily dose with reporting threshold 0.1%, identification threshold 0.2%, and qualification threshold 0.5%, ICH Q3D elemental impurity testing, and 21 CFR 211.84 identity, potency, and impurity testing of the incoming TAF fumarate lot. Terminal finished product types are film-coated immediate-release antiretroviral combination tablets containing 10 mg or 25 mg TAF fumarate with emtricitabine, bictegravir, rilpivirine, or elvitegravir/cobicistat; no sustained-release coating is applied because the immediate-release dissolution profile drives TAF fumarate conversion to tenofovir in target cells.

What Process Controls Prevent Hydrolytic Degradation During Wet Granulation?

In high-shear granulation, aqueous binder addition is tolerated only when the granulating liquid is pre-chilled to 2–8°C and the API is protected from prolonged residence time in the wet mass. TAF fumarate is a low-dose, hygroscopic active pharmaceutical ingredient with pH-dependent aqueous phase stability; therefore, a 25 L high-shear granulator with a 100 mm main blade and side chopper is operated at main impeller 200–400 rpm and chopper 1,000–1,500 rpm, with a liquid addition rate of 30–60 g/min per kg dry mass. The drug substance is pre-dried at ≤45°C to moisture not more than 0.5% w/w by USP <921> Method Ia before weighing. Granulation endpoint is controlled by power consumption 5–8 N·m or by a 2–5 minute wet massing time after the binder solution has been added; the endpoint window is intentionally narrow because over-massing leads to densification, slower liquid penetration into the dried granule bed, and dissolution slowdown. Alkaline granulating fluids and sodium bicarbonate are avoided because hydrolysis of the isopropyl ester is accelerated above pH 5.0. If the wet mass is discharged through a 4 mm square-hole screen and transferred to a fluid-bed drier within 15 minutes, hydrolytic degradation is minimized; inlet air temperature is 50–60°C, and product temperature is maintained below 40°C until loss-on-drying is NMT 1.0%–1.5% w/w.

Formulation addition ratio for the tablet core is 2.5%–5.0% w/w TAF fumarate for the 25 mg HBV monotherapy strength, with intragranular mannitol at 40%–60% w/w, microcrystalline cellulose at 20%–35% w/w, and extragranular croscarmellose sodium at 3%–5% w/w; hypromellose 2910 binder is applied as a 4% w/w aqueous solution at 2%–4% w/w of dry granule mass. Incoming API particle size is controlled by laser diffraction per USP <429> with D90 ≤ 30 µm under ICH Q6A decision tree studies, because larger particles slow dissolution from the compressed wet-granulated matrix. Dried granules are passed through a 600 µm screen, blended with extragranular excipients in a 300 L bin blender at 12 rpm for 15 minutes, lubricated with magnesium stearate 0.5% w/w for 3 minutes, and compressed at main compression force 8–18 kN to tablet hardness 100–140 N. Release testing under 21 CFR 211.160 includes USP <711> dissolution, USP <905> uniformity of dosage units with acceptance value ≤ 15.0, USP <701> disintegration, ICH Q1A(R2) accelerated stability at 40°C ± 2°C / 75% RH ± 5% RH for 6 months, and ICH Q3D elemental impurity analysis. Published data for wet granulation of TAF fumarate is limited; therefore, the drying endpoint is confirmed by pilot-scale moisture and dissolution data before commercial batch release. Terminal products are film-coated immediate-release 25 mg TAF fumarate tablets for chronic hepatitis B monotherapy; the non-functional Opadry II coating is applied at 3%–4% w/w weight gain to mask bitterness without altering dissolution.

Capsule filling for low-dose TAF fumarate blends and flow-aid selection

The decision to use a capsule presentation instead of a tablet for low-dose TAF fumarate is driven by dose-blending demands in clinical trial supplies and dysphagia-related patient populations, not by a superior compressibility profile. At fill weights below 300 mg for size 1 hard HPMC or gelatin capsules, the angle of repose of a 25 mg TAF fumarate blend containing mannitol and croscarmellose sodium is reduced to ≤38° by blending 1.0%–2.0% w/w fumed silica before final lubrication with magnesium stearate 0.5% w/w for 3 minutes in a low-shear V-blender. TAF fumarate is present at 8%–12% w/w of the filled capsule contents at the 25 mg dose with a total fill weight of 200–300 mg; for a 10 mg dose capsule, the fraction is 3%–5% w/w. Encapsulation is performed on an intermittent-motion capsule filler with dosator nozzle diameter 5.0 mm; fill weight is maintained within ±5% of target, and empty shells are conditioned at 15–25°C and 35%–55% RH for 24–48 h to prevent shell brittleness. If ambient relative humidity exceeds 60% RH, encapsulation is suspended because capsule shells become tacky and fill weight variability increases. Terminal products are hard gelatin or HPMC capsule presentations at 10 mg or 25 mg TAF fumarate for HIV/HBV dose-ranging and blinded clinical studies.

Release testing includes USP <711> dissolution of the capsule contents, USP <905> uniformity of dosage units, USP <616> bulk and tapped density, USP <1174> powder flow, 21 CFR 211.166 stability testing, and ICH Q3D elemental impurity limits. Bulk density below 0.45 g/mL is controlled because it degrades flow into the dosing disc and increases fill weight variability; when bulk density falls below this limit, the fumed silica concentration is raised stepwise within the 1.0%–2.0% w/w range and the blend is re-tested for angle of repose and compressibility index. Hygroscopic deliquescent fillers are avoided because free moisture accelerates TAF fumarate hydrolytic degradation in the filled capsule.

When granules for oral suspension require fluid-bed spray rate and dew point control

A fluid-bed rotor granulation route is selected when the finished unit is not a monolithic tablet but a sachet or sprinkle granule for once-daily TAF fumarate dosing below 25 mg. The drug is layered onto microcrystalline cellulose spheres of 250–355 µm in a Glatt GPCG-3 with a Wurster insert; inlet air dew point is maintained at −10°C to 0°C and spray rate is 8–15 g/min per kg of spheres to prevent surface over-wetting and agglomeration. The TAF fumarate layering dispersion contains the drug substance at 1.0%–5.0% w/w of the finished granule mass, hypromellose 2910 as a binder at 10% w/w of the dispersion solids, and talc at 5% w/w of dry matter as an anti-tack agent. Product temperature is maintained at 25–35°C with outlet air temperature 30–38°C; after layering, the granules are dried to moisture NMT 1.0% w/w by USP <921> and screened through a 500 µm sieve to reject oversized agglomerates. Polyethylene glycol layering binder is avoided because it increases tack and agglomeration at product temperature above 30°C. Published data for this specific configuration is limited because no commercial TAF fumarate granule product is widely marketed; therefore, the drying endpoint is confirmed by forced degradation studies rather than by reference product comparison.

For granules, 21 CFR 211.110(a) sampling is performed at sachet filling heads; particle size distribution is determined by USP <786> analytical sieving, and dissolution of the released granules is measured by USP <711> after dispersing the dose in 900 mL of 0.01 N HCl. Content uniformity is evaluated by weight variation where the sachet is a single-dose container, and ICH Q1A(R2) long-term stability is run at 25°C ± 2°C / 60% RH ± 5% RH with ICH Q3B(R2) degradation product monitoring and ICH Q3D elemental impurity analysis. Filling into sachets uses a vertical form-fill-seal line with an auger filler at fill weight 1 g or 2 g; fill tolerance is ±5%, and seal integrity is tested by peel strength according to ASTM F88/F88M-21. Terminal products are finished granules in single-dose sachets, powder for oral suspension upon reconstitution, and multi-particulate sprinkle capsules where the granules are over-encapsulated for age-stratified dosing.

Parenteral feasibility limits: pH, aqueous solubility, and terminal sterilization incompatibility

For injectable presentations, the pH-dependent aqueous solubility of tenofovir alafenamide fumarate constrains formulation to a buffered aqueous solution at pH 3.0–4.0 or a lyophilized cake for reconstitution; published data for this specific configuration is limited because no commercial immediate-release injectable is currently approved in major markets. The fumarate salt has higher aqueous solubility than the free base, but the isopropyl ester prodrug may undergo ester hydrolysis as aqueous pH increases; therefore, terminal sterilization by saturated steam at 121°C for 15 minutes is generally avoided in favor of aseptic filtration through a 0.22 µm PVDF membrane. A 10 mg/mL solution formulation places the API at 1.0% w/v with 10–50 mM acetate or citrate buffer; a lyophilized presentation may use pre-lyophilization drug concentration of 5–20 mg/mL with 2%–5% w/v mannitol or trehalose as cryoprotectant. Aqueous solutions held above pH 5.0 are not retained for more than 24 h at 2–8°C because ester hydrolysis may increase related substances above ICH Q3B(R2) thresholds.

Compounding is performed in an ISO 7 environment under closed transfer conditions; the filtered solution is filled into Type I borosilicate glass vials with butyl rubber stoppers under an ISO 5 laminar air flow. Lyophilization, where selected, uses a shelf freezing step at −40°C, primary drying at −20°C to +10°C under 100–200 mTorr chamber pressure for 48–72 h, and secondary drying at 25–30°C for 12–24 h until residual moisture is NMT 1.0% w/w by USP <921>. Injectable release testing includes USP <1>, USP <85> bacterial endotoxins with a limit calculated from the maximum bolus dose, USP <71> sterility by membrane filtration after 14-day incubation, USP <788> particulate matter in injections with light obscuration counts not exceeding 6,000 particles at ≥10 µm and 600 particles at ≥25 µm per container for the small-volume parenteral presentation, 21 CFR 211.94 container-closure integrity, and ICH Q3C residual solvent analysis for tertiary solvents used in the pre-filtration solution. Terminal products are development-stage lyophilized powder for injection or aqueous solution for injection in single-dose vials for clinical trial material, not a commercialization-ready parenteral line.