Quinurone Sulfate (Acaprin) Veterinary Grade API is released as a multi-dosage-form active substance for direct incorporation into tablets, injections, capsules, powders, granules, premixes, and solutions. The product model designations are the standard milled grade, the micronized injectable grade, and the low-dust granulated premix grade. The standard milled grade is supplied with a D90 not more than 250 µm and bulk density 0.40–0.60 g/cm³; the micronized injectable grade is supplied with a D50 not more than 10.0 µm; and the low-dust granulated premix grade is supplied with a D10 not less than 75 µm to reduce airborne dust during transfer. The sulfate counter-ion is determined by ion chromatography and is critical to aqueous solubility and pH behaviour; the free base form is substantially less water-soluble and is not interchangeable without revalidation of dissolution and bioavailability. The name is also encountered as quinuronium sulfate in older veterinary literature; the manufacturer’s certificate should confirm nomenclature against the approved reference standard because salt stoichiometry and hydrate form may differ between sources. The active substance appears as a white to pale yellow crystalline powder, and any colour change to amber or brown indicates light- or metal-catalysed degradation. Manufacturing is conducted under ICH Q7 and EU GMP Part II, with batch traceability through raw material synthesis, micronization, blending, and final API packaging. Certificate of analysis documentation includes identity by infrared absorption, assay by high-performance liquid chromatography, related substances by area normalization, loss on drying, residue on ignition, heavy metals, residual solvents according to ICH Q3C, elemental impurities according to ICH Q3D, and microbial enumeration according to Ph. Eur. 2.6.12.

Specification Control Is Product-Form-Specific Rather Than a Single Fixed Monograph

The acceptance criteria must be differentiated by dosage-form route. Tablet and capsule applications require close control of flow character, as indicated by Carr index and Hausner ratio, whereas injectable and solution applications require stricter control of endotoxin, particulate matter, and bioburden. A representative solid-oral grade is tested against loss on drying not more than 0.5% w/w by USP <731>, residue on ignition not more than 0.1% w/w by Ph. Eur. 2.4.14, and heavy metals not more than 10 ppm by Ph. Eur. 2.4.8 method C. Assay is specified from 98.0% to 102.0% on the dried basis, with total related substances not more than 2.0% and any individual specified impurity not more than 0.10%. For parenteral grades, bacterial endotoxin is not more than 0.5 EU/mg by Ph. Eur. 2.6.14, and total aerobic microbial count is not more than 10² CFU/g with total yeast and mould count not more than 10¹ CFU/g by Ph. Eur. 2.6.12. Residual solvent limits follow ICH Q3C for Class 1, Class 2, and Class 3 solvents; elemental impurity limits follow ICH Q3D as applied to veterinary products. Particle size distribution is determined by laser diffraction using wet or dry dispersion according to ISO 13320-1; the standard grade is required to have not more than 5.0% of particles below 10 µm to avoid dusting, while the micronized injectable grade is required to have a D10 not more than 2.0 µm to reduce needle blocking.

What Solvent and pH Conditions Govern Reversible Precipitation in Injectable Aqueous Vehicles?

For injectable solutions, the sulfate salt is first dispersed in Water for Injections at 20–25°C, and the pH is adjusted with dilute hydrochloric acid to 3.5–4.5. At this pH, the protonated quinurone species remains in solution, and filtration through a 0.22 µm polyvinylidene fluoride or polyethersulfone membrane is typically feasible. Above pH 6.5, the free base precipitates as a poorly wettable floc; once formed, re-acidification does not fully restore the original particle size distribution, and the batch must be reworked or discarded. This precipitation threshold defines a critical process parameter in scales above 50 L, where pH drift from dissolved carbon dioxide and buffer depletion can generate inhomogeneity in the vessel. Stainless steel 316L tanks are preferred; copper, iron, and brass fittings must be excluded because metal cations accelerate the formation of coloured degradation products. Dissolved oxygen is controlled by nitrogen sparging to below 0.5 mg/L before compounding. Terminal sterilization at 121°C for 15 min may be evaluated only if the formulation remains within specification for related substances after the cycle; if chromatographic data show an increase in total impurities greater than 0.5% area, transition to aseptic filtration is required.

When Direct Compression Replaces Wet Granulation, Controlling Particle Morphology Becomes the Primary Blend Homogeneity Risk

Direct compression of low-dose quinurone sulfate tablets is feasible when the API particle size is matched to direct-compression lactose or microcrystalline cellulose to reduce segregation. The standard milled grade is pre-blended with microcrystalline cellulose at 20–30% w/w and lactose monohydrate at 60–70% w/w. Crospovidone or croscarmellose sodium at 2.0% w/w is added as disintegrant, and magnesium stearate at 0.25–0.50% w/w is added after main mixing. Blending is performed in a bin blender at 10–12 rpm for 300–600 revolutions, after which blend uniformity samples are drawn from at least 10 positions and tested by HPLC. Compression is performed on a rotary tablet press with a turret speed of 30–60 rpm and pre-compression force of 2–4 kN; main compression force is adjusted to maintain tablet hardness 5–8 kp and friability not more than 1.0% by USP 1216. Disintegration time in water at 37°C should not exceed 15 min by USP 701. If compressibility is insufficient, wet granulation with a starch paste or polyvinylpyrrolidone solution at 2.0–3.0% w/w is used; however, the granulation solvent must be removed to a final moisture not more than 3.0% w/w because residual water increases cohesion and causes picking on tablet punches.

In capsule filling, the blend is processed on a tamping pin machine or dosator capsule machine with a target fill weight error less than 5.0% per capsule. The milled grade is often dry-granulated by roller compaction when the API concentration is above 10% w/w because direct blend flow is too poor. Roller compaction with a compaction pressure of 20–30 kN/cm produces ribbons that are milled through a 1.0 mm screen; the resulting granules are lubricated and filled into size 0 or 1 hard gelatin or HPMC capsules. For feed powders and premixes, the API is first adsorbed onto calcium carbonate or precipitated silica to reduce hygroscopicity and improve distribution in the feed. A 5.0% w/w pre-blend is prepared in a ribbon blender at 15–20 rpm for 10 min, then diluted geometrically to the target 0.2–1.0% w/w premix. The finished premix is sampled from 10 locations and analysed for assay; acceptance is replicate mean 90.0–110.0% of label claim with relative standard deviation not more than 5.0% by USP 905 or Ph. Eur. 2.9.40. Granulation for feed premixes is carried out in a high-shear granulator with water or starch paste at 20–30% w/w liquid addition; the wet mass is dried in a fluid-bed dryer to moisture not more than 3.0% w/w, and the dry granules are screened to remove particles larger than 1.0 mm.

Salt-Form Differentiation Against Diminazene Aceturate and Imidocarb Dipropionate in Veterinary Antiprotozoal Therapy

Quinurone Sulfate (Acaprin) is differentiated from other veterinary antiprotozoal active substances by its sulfate salt chemistry, its historical use in acute piroplasmosis treatment, and its formulation behaviour. Diminazene aceturate is a diaceturate salt intended mainly for deep intramuscular injection, whereas quinurone sulfate is described in older veterinary references for subcutaneous administration; the tissue tolerance and local reaction profiles therefore are not directly interchangeable. Imidocarb dipropionate is used for both treatment and prophylaxis and is retained in tissues for extended periods; quinurone sulfate is regarded as an acute treatment with a shorter protective window, although published head-to-head residue depletion data remain limited. In formulation development, the sulfate salt is freely soluble in acidified aqueous vehicles, but the solution is more sensitive to light and heavy-metal catalysis than solid dosage forms. Strong alkalies, oxidizing agents, and cationic surfactant systems are incompatible because they promote precipitation, degradation, or loss of active content. The active substance should not be mixed with copper, iron, or nickel surfaces during milling, blending, or liquid compounding. Where comparison with a reference product is required, bioequivalence and residue studies must follow the national regulatory guidance for the target species, and no claim of identical therapeutic margin can be made without species-specific pharmacokinetic data. Cross-resistance against diminazene-resistant isolates should not be assumed; susceptibility testing on the target parasite population is required before selecting quinurone sulfate over alternative agents.

For oral solutions and drinking-water formulations, the API is dissolved in acidified water at pH 3.0–4.0, and a stabilizer may be required if the solution is to be stored beyond 24 h. The solution should be packaged in amber polyethylene terephthalate or polypropylene containers with closure seals, and the primary packaging is qualified for light transmission according to USP 671; transparent or white low-density polyethylene containers are not acceptable for leave products exposed to daylight. Long-term storage of the dry API requires low-oxygen and low-light conditions; storage at 25°C with relative humidity not more than 60% is recommended. Above 60% RH, the milled powder may absorb moisture and form aggregates; drying is required before processing at high relative humidity. The material is re-sealed under nitrogen after each container opening, and bulk packaging should be limited to containers with moisture-tight liners.

Forced-degradation studies under ICH Q1B are used to establish that the analytical method can separate the active peak from photodegradation products. In the solid state, exposure to UV and visible light generates a yellow-brown discolouration and an increase in a specified oxidative impurity; the impurity is quantified at relative retention time 0.85 against the active peak in a typical reversed-phase system. In solution, oxidative degradation is accelerated by hydrogen peroxide and by transition-metal ions at trace levels; the main degradation products should be separated with a resolution not less than 2.0 between critical pairs. Process analytical technology based on near-infrared reflectance can be used for blend homogeneity monitoring at a target concentration of 5.0% w/w or higher; below that concentration, online HPLC or periodic sampling is required. The API is compatible with most standard excipients used in veterinary oral solid dosage forms, but prolonged contact with alkaline buffers, strong desiccants, and iron oxides used as colourants should be avoided. Batch-to-batch variability in sulfate content and particle size distribution is controlled by supplier qualification and incoming material testing; the user should require a supplier change notification before any change in crystallisation solvent, milling equipment, or drying conditions.