Fluralaner direct-compression chewable tablets for canine administration are designed around a fixed 25 mg/kg body mass dose. The commercial tablet line covers body masses of 4.5 kg, 10 kg, 20 kg, 40 kg, and 56 kg with strengths of 112.5 mg, 250 mg, 500 mg, 1000 mg, and 1400 mg. Because fluralaner belongs to the isoxazoline class and is classified as practically insoluble in water under pharmacopoeial solubility definitions, immediate-release oral solid dosage performance depends on rapid wetting and dispersion of the micronized API rather than dissolution-driven solution kinetics. Direct compression begins with a pre-blend of fluralaner and a hydrophilic filler such as spray-dried lactose monohydrate at a 1:3 active-to-filler ratio, passed through a 500 µm mesh to break agglomerates, then added to a bin blender charged to 60% of working volume. Final lubrication with 0.5% w/w magnesium stearate for 3 min prevents over-lubrication; blending beyond 5 min decreases tablet hardness and increases disintegration time in routine quality control. Croscarmellose sodium at 2–4% w/w is added intragranularly to maintain disintegration below 15 min in water at 37°C, measured by Ph. Eur. 2.9.1. Uniformity of dosage units is assessed according to USP <905> with an acceptance value of ≤ 15.0 at release, while blend uniformity is controlled to a relative standard deviation below 5.0% under FDA Guidance for Industry Powder Blends.

Compression is performed on a rotary tablet press fitted with European D tooling. Target hardness is 90–120 N, and friability is maintained below 1.0% according to USP <1216>. The low aqueous solubility of fluralaner requires dissolution testing in 900 mL of pH 6.8 phosphate buffer containing 0.5% sodium lauryl sulfate at 75 rpm using USP Apparatus 2. The food effect observed with oral fluralaner in dogs requires dosing with food; this is recorded in the registered label and is not directly governed by the dissolution specification but affects in vivo Cmax and AUC. Packaging for chewable tablets uses desiccant-capped HDPE bottles with induction-sealed closures. Dry-blend moisture is controlled to ≤ 2.0% w/w before compression, and bulk storage conditions are maintained at 25°C/60% RH for Zone IIb stability studies. The 12–15 day plasma elimination half-life in dogs supports the 12-week redosing interval, so release-rate acceleration beyond immediate-release criteria is not required for sustained ectoparasite activity.

How Drinking-Water Proportional Dosing of Fluralaner Is Constrained by Water Hardness and pH

In registered poultry finished products, fluralaner is delivered at 0.5 mg/kg body mass twice, with the two doses separated by 7 days. The concentrated oral solution is supplied at 10 mg/mL and diluted into drinking water before distribution through nipple or bell drinkers. For a flock biomass of 1,000 kg, the stock solution volume per administration is 50 mL, because 0.5 mg/kg multiplied by 1,000 kg equals 500 mg of fluralaner, and 500 mg divided by 10 mg/mL equals 50 mL. Medicated water concentration after a 1:1,000 dilution is 10 µg/mL. Proportioner pumps for in-line dilution are calibrated to 1–5% stock rates; active concentration at the drinker line should not deviate more than 5% coefficient of variation, which is verified by HPLC-UV at the point of consumption.

The twice-seven-day schedule requires two separate stock preparations, and diluted medicated water is used within 24 h at 25°C. Water quality matters because fluralaner is practically insoluble; the concentrate depends on a glyceryl-based co-solvent and non-ionic surfactant system to produce a colloidal dispersion upon dilution. Hard water with total hardness above 250 mg/L as calcium carbonate and pH above 7.6 can accelerate phase separation in the drinker line; this is an operational incompatibility rather than a chemical degradation pathway. Ultraviolet exposure accelerates photodegradation of the isoxazoline ring, so light-protected holding tanks are required. Compliance for the registered solution includes residue limits under Commission Regulation (EU) No 37/2010; egg withdrawal is 0 days for the original product, but this must be revalidated for any generic formulation because excipient changes alter residue depletion in liver and skin–fat compartments. Microbial enumeration tests follow Ph. Eur. 2.6.12 and 2.6.13, and packaging is amber glass or aluminium-sealed polyethylene terephthalate to limit headspace oxygen.

Poultry Water-Dispersible Granule Processing

Published data for market-authorized fluralaner water-dispersible granules is limited; the process described is a design route using standard veterinary granulation equipment. A granulated oral presentation becomes necessary when dry storage and in-line powder proportioning are required instead of liquid stock concentrates. High-shear wet granulation is used with a drug load of 2–5% w/w fluralaner in a lactose monohydrate matrix. A binder solution of povidone K30 at 5% w/w in purified water is added over 3–5 min in a laboratory-scale granulator with impeller speed 300 rpm and chopper speed 1,500 rpm; endpoint moisture is 12–18% w/w. The wet mass is dried in a fluid-bed dryer with inlet air at 60°C until loss on drying is ≤ 2.0% w/w, then sieved through 850 µm. Fines below 150 µm are kept below 15% w/w to avoid dusting and poor flow in volumetric proportioners.

Wetting of the granule in drinking water is rate-limiting because the isoxazoline API is hydrophobic; 0.1% w/w sodium lauryl sulfate is distributed on the granule surface before final blending. Dispersibility testing at 25°C in a 100 mL graduated cylinder with 2 min stirring requires 90% of granules to pass through 180 µm wet sieving. The finished granule is packaged in aluminium foil laminate pouches with a desiccant; moisture ingress above 2.5% w/w causes granule hardening and redispersibility failure within 6 months at 30°C/65% RH. Particle-size distribution is controlled by Ph. Eur. 2.9.12 sieve analysis, and bulk density is maintained between 0.45 g/mL and 0.60 g/mL to improve automatic dosing accuracy. No granular finished product for fluralaner is listed in EU veterinary databases; therefore each batch must be supported by in-house stability data before field use.

For exploratory pharmacokinetic dose-ranging in feline and canine models, hard gelatin capsules are prepared in a low-humidity suite at 30–35% RH from fluralaner API that has been jet-milled to a particle-size D90 below 30 µm and pre-blended in a turbula mixer at 30 rpm for 15 min. Capsule strengths of 5 mg, 25 mg, 100 mg, and 250 mg are filled manually or with a semi-automatic capsule machine; each capsule uses a 1:9 ratio of API to lactose monohydrate with 0.5% w/w fumed silica as glidant. Content uniformity is assessed with USP <905> at an acceptance value ≤ 15.0. Dissolution uses USP Apparatus 2 at 75 rpm in 900 mL of 0.5% sodium lauryl sulfate in pH 6.8 buffer; release is rapid after shell rupture, making shell cross-linking from aldehyde impurities in lactose or capsule preservatives a critical control point at 40°C/75% RH. The capsule presentation is a clinical trial material configuration, not a registered veterinary finished product.

Batch release includes USP <701> disintegration testing for capsules; the gelatin shell must rupture within 10 min in water at 37°C. Because fluralaner is highly protein-bound and has a long elimination half-life, capsule formulations do not require enteric coating; the goal is simple immediate release after oral gavage or voluntary ingestion. Fed-state administration is used to match the licensed oral tablet food effect, while fasted-state capsules may produce lower Cmax but similar AUC; the fed condition is therefore treated as the reference condition for comparative studies.

When a Multi-Month Subcutaneous Depot Is Requested Despite the Absence of an Approved Parenteral Finished Product

Because fluralaner is practically insoluble in aqueous media and exhibits high plasma protein binding exceeding 99%, development of a long-acting subcutaneous injection is constrained by the need for non-aqueous suspension technology rather than simple aqueous solution. No injectable fluralaner finished dosage form is currently identified in the US FDA Animal Drugs database, and published data for this specific configuration is limited. A pilot-scale parenteral suspension is prepared under development conditions with fluralaner micronized to D90 ≤ 10 µm and dispersed in a 50:50 v/v benzyl benzoate–ethyl oleate vehicle containing 0.5% w/w aluminium monostearate as suspending agent. Vehicle viscosity is adjusted to 80–150 mPa·s at 25°C to provide syringeability through a 21G needle while preventing rapid sedimentation. Sedimentation volume after 24 h is controlled above 0.8, with redispersibility by manual shaking for 30 s.

Sterility assurance for the oily suspension follows USP <71>; the vehicle is dry-heat-sterilized at 180°C for 2 h, and the API is either gamma-irradiated at 25 kGy if forced degradation shows < 0.2% total degradants, or micronized aseptically. Radiation-induced degradation data for fluralaner is limited and must be generated before terminal sterilization is claimed. Particulate matter is tested by USP <788> for injectable suspensions. Syringeability force should remain below 25 N at 1 mL/s through a 21G needle; higher force indicates excessive flocculation. Residual solvent testing is governed by VICH GL18. Because no approved reference product exists, in vivo dose confirmation in target species is required before field use.

Fluralaner Compounded Oral Suspensions for Small Mammals Are Limited by Sedimentation Volume

Veterinary hospital compounding of fluralaner oral suspension from bulk API is performed only when the licensed chewable tablet cannot be dose-adjusted for small companion mammals or avian patients. In this context, USP <795> and FDA CPG 608.400 apply. The API is levigated with glycerol at a 1:1 ratio, then dispersed in an aqueous suspending vehicle containing microcrystalline cellulose, carboxymethylcellulose sodium, and sodium benzoate at 5–20 mg/mL. Concentrations above 20 mg/mL produce flocculation and irreversible caking because the hydrophobic API forms oily agglomerates; a wetting agent such as polysorbate 80 at 0.1% w/w is added before dispersion. The compounded suspension is stored at 2–8°C and assigned a 14-day beyond-use date in the absence of stability data. Bioavailability from an aqueous suspension may be lower than from an oil-based solution because fluralaner dissolution from hydrophobic particles is rate-limited in the gastrointestinal tract; shaking before administration is essential to avoid under-dosing from settled API.

Scale-up from a 100 mL hospital batch to a 2 L dispensing batch requires propeller mixing at 200 rpm; a high-shear mixer is avoided because it introduces heat and may reduce suspension viscosity. The final suspension is tested for sedimentation ratio at 24 h; a ratio below 0.8 indicates the need to increase microcrystalline cellulose from 1.0% w/w to 1.5% w/w. Single-dose syringes should be clear to verify homogeneity before dosing.