When Roller Compaction Replaces Direct Compression for Micronised Griseofulvin Tablets

In companion animal dermatophytosis protocols, oral griseofulvin is administered to dogs at total daily dosages commonly cited between 25 mg/kg and 50 mg/kg, divided into two equal feeds. Feline protocols frequently require higher weight-normalised intakes near 50 mg/kg/day, making a 125 mg scored tablet the dose-division tool for a 4–5 kg cat. The micronised Griseofulvin Veterinary Grade API is specified with a particle-size ceiling because griseofulvin dissolution is the bioavailability-limiting step. Suppliers should provide a laser diffraction report under USP <429> or Ph. Eur. 2.9.40 with D90 not exceeding 10 µm; milled material with D50 values above 3 µm transfers slower into the 0.2% (w/v) sodium lauryl sulfate dissolution medium of USP <711> apparatus 2 at 75 rpm and 37 °C ± 0.5 °C. Tablet formulations are blended on a 24-inch V-shell blender at 20 rpm for 15 min with baffles to limit dead-zone accumulation of needle-like crystals. Typical core loads are 40–50 wt% active: a 250 mg tablet therefore has a total core mass of 500–625 mg, with lactose monohydrate 25–35 wt%, microcrystalline cellulose 20–30 wt%, croscarmellose sodium 2–5 wt%, and magnesium stearate 0.5–1.0 wt%. Direct compression is excluded when the blend flow function coefficient falls below 2.0; the needle-like habit creates bridging at feed frame speeds above 30 rpm on rotary presses. Roller compaction is therefore used before tableting.

Roller compaction operates with roll force of 25–35 kN and gap 1.0–1.5 mm, followed by an oscillating granulator with 1.0 mm mesh. The granulate is screened to a D50 between 150 µm and 300 µm. Tablets are compressed at 15–20 kN on a 10-station instrumented press to hardness 50–80 N under USP <1217>; a lower hardness target below 40 N produces edge chipping during film coating, while hardness above 100 N extends disintegration beyond 15 min in 37 °C water. Friability is controlled below 0.8% under the rotation conditions of USP <1216> or Ph. Eur. 2.9.7. Batch-to-batch variation of micronised API surface area is the principal cause of content non-uniformity; acceptance follows USP <905> with an acceptance value not more than 15. Stability protocols follow VICH GL3 with storage at 40 °C ± 2 °C and 75% RH ± 5% RH for 6 months in aluminium/aluminium blisters. Finished dosage types include 125 mg and 250 mg scored tablets and 125 mg capsules for canine and feline patients requiring extended treatment under veterinary supervision.

Aqueous oral suspensions for neonatal kittens and low-body-weight dogs require dose flexibility that solid oral dosage forms cannot provide reproducibly because body weights below 1.5 kg create sub-tablet increments of less than 31.25 mg. The compounded suspension does not fall under a single commercial monograph; it is prepared under the nonsterile compounding standard of USP <795> and requires beyond-use dating supported by vessel-specific stability documentation. A typical formulation contains micronised griseofulvin at 25 mg/mL or 50 mg/mL, sodium carboxymethylcellulose at 0.5% w/v, glycerin at 10–20% v/v, polysorbate 80 at 0.1% v/v, sorbitol at 20% w/v, and sodium benzoate at 0.1% w/v. The API is first levigated with glycerin to break electrostatic agglomerates, then dispersed into the vehicle with an overhead high-shear mixer at 1,200 rpm for 20 min; after hydration, a rotor-stator homogeniser is passed at 3,000 rpm for 10 min to reduce visible aggregates. pH is adjusted to 4.0–6.0 with 10% w/v citric acid or 10% w/v sodium citrate; exposure above pH 7.5 accelerates hydrolytic ring-opening of the benzofuran moiety, so bicarbonate buffers are incompatible. A viscosity range of 150–400 mPa·s at 25 °C is measured with a Brookfield LV spindle 63 at 6 rpm. Storage in 30 mL, 60 mL, or 100 mL amber polyethylene terephthalate bottles with press-in bottle adaptors permits oral syringes of 1 mL and 5 mL. Elevated sedimentation after 72 h requires re-dispersion testing under ISO 13320 laser diffraction on the homogenate; published data for long-term stability in this specific configuration is limited, and the clinical use period should not exceed 28 days at 15–25 °C unless additional antimicrobial effectiveness testing under USP <51> establishes otherwise. Terminal dosage types are 30 mL, 60 mL, and 100 mL oral suspension bottles for dose rounding in low-weight patients.

Equine Top-Dress Granules: Palatability Buffering and Gastric Transit in Adult Horses

In equine dermatophytosis protocols lasting 7–21 days, adult horses reject direct intubation for an antifungal that must be dosed repeatedly, so oral granules top-dressed on a small volume of concentrate are used when barn-level compliance is the limiting factor. The equine daily dosage often cited in older veterinary formulary records is 5 mg/kg per day, which for a 500 kg horse requires 2.5 g/day of active substance. A granule strength of 250 mg/g active substance yields a 10 g daily top-dress unit, which is low enough to avoid substantial interference with total daily dry matter intake. Production-scale manufacturing is performed on a fluidised bed rotor granulator with inlet air temperature 50–60 °C, product temperature 35–40 °C, and spray rate of 20–30 g/min for a 2% w/v hydroxypropyl methylcellulose binder solution. The granulation charge includes lactic acid-treated apple pomace powder at 10–20 wt% and dried molasses extract at 5–10 wt% to mask the bitter taste; these carriers also increase wetting because the API itself is hydrophobic. Final moisture after drying is controlled below 2.0% by loss on drying at 105 °C, and the dried granulate is sieved through a 0.8 mm screen to a D50 of approximately 700 µm. A final 0.5 wt% vegetable oil coating on the granules reduces electrostatic dusting during auger filling into sachets. The finished sachet is filled with a belt-fed auger at a target weight variation not exceeding ±5%; content uniformity follows USP <905> on 10 units. Dissolution testing for the granule may be adapted from USP <711> apparatus 2 with 0.2% (w/v) sodium lauryl sulfate at 75 rpm; because the dosage form is mixed with feed, the in vivo release is slowed by gastric retention and feed-matrix partitioning. Published data for this delayed-release interaction in equine feed matrices is limited. Stability is monitored under VICH GL3 at 25 °C ± 2 °C and 60% RH ± 5% RH in heat-sealed aluminium sachets. Manufacturing for a registered equine product within the European Economic Area operates under Regulation (EU) 2019/6; in jurisdictions without a registered equine oral granule, veterinary compounding under USP <795> may be the applicable route. Terminal dosage types are 10 g sachets and 1 kg bulk veterinary granules for stud farms and equine hospitals.

Because approved tablet strengths cannot be subdivided for small felids, mustelids, rabbits, or birds, veterinary hospitals and zoological pharmacies frequently require capsule dosage forms in non-commercial strengths. The compounding workflow is governed by USP <795> for nonsterile preparations; when the capsule is intended for species with unknown metabolic sensitivity, the prescription should be supported by allometric scaling literature, and no therapeutic claim is made without a species-specific published reference. Low-strength capsules are prepared with micronised griseofulvin at 10 mg, 25 mg, or 50 mg per capsule using size 3 or 4 hard gelatin or hydroxypropyl methylcellulose capsules. The active fraction may range from 1–15 wt% of the final fill mass; lactose monohydrate is used as the diluent after compatibility testing because direct replacement with mannitol can increase triboelectric charging of the needle-like crystals. Geometric dilution is performed on a 250 µm stainless steel sieve until the mixture passes through without visible API flecks; the batch is then blended in a low-shear turbula mixer at 46 rpm for 10 min. Manual capsule filling is carried out with a 100-hole capsule machine; each capsule is weighed and sorted to a weight variation not exceeding ±5%, and content uniformity is checked on 10 units under USP <905>. Capsule shells are stored in sealed containers at 20–25 °C; moisture ingress above 60% RH causes the gelatin shell to soften and the micronised powder to form a non-redispersible plug. The terminal dosage types are 10 mg, 25 mg, and 50 mg capsules packed in 20-count, 50-count, and 100-count containers. Because short-course antifungal therapy in exotic mammals often requires hiding the capsule in a small amount of carnivore diet, a dissolution delay introduced by the feed matrix should be evaluated using USP <711> apparatus 2 at 37 °C in 0.2% (w/v) sodium lauryl sulfate; published data on this feed-interaction configuration is limited.

What Limits Injectable Formulation Development for Griseofulvin Veterinary API Despite Its BCS Class II Profile?

Parenteral administration of griseofulvin is not the established veterinary clinical route because the substance exhibits an aqueous solubility below approximately 10 mg/L at 25 °C, and injectable dose volumes for a 10–20 kg dog would require co-solvent loads that carry precipitation and haemolysis risk. If a sterile injectable development is initiated for a specific veterinary indication, the formulation work must address the solubility gap while observing the sterility and particulate requirements of USP <1>, USP <788>, USP <85>, and VICH GL18. Co-solvent modelling with PEG 400, ethanol, and benzyl alcohol indicates that a 30–40% v/v PEG 400 system with 10% v/v ethanol may solubilise griseofulvin to approximately 2–5 mg/mL; however, dilution with 0.9% w/v sodium chloride in the syringe line causes immediate precipitation and particle growth above the 10 µm limit of USP <788> Method 1 light obscuration. Terminal heat sterilisation is not feasible at 121 °C for 15 min because the weakly basic lactone is prone to hydrolytic degradation above pH 7.0; aseptic fill-finish inside an ISO 14644-1:2015 Class 5 cleanroom with 0.22 µm membrane filtration is the only practical containment strategy, but membrane filtration removes the poorly soluble fraction and lowers content uniformity. Residual solvent limits in veterinary injectables must follow VICH GL18; PEG 400 and ethanol are not classed as residual solvents requiring a monograph limit, but benzyl alcohol is a contraindicated excipient in cats at concentrations above 1% v/v because feline erythrocytes are vulnerable to oxidative injury. Published data for a licensed veterinary griseofulvin injectable are limited; therefore, the terminal dosage type would be an experimental 10 mL or 20 mL single-use amber borosilicate vial containing a sterile suspension rather than a true solution. A manufacturing dossier for this configuration would require filter compatibility studies, particle-size stability over 24 h, and injection-site tolerance data before any clinical use.