Zoxamide Veterinary Grade API is a crystalline benzamide fungicide active substance supplied as a non-sterile raw material for further processing into tablets, injections, capsules, powders, granules, premix, and solutions. The substance is identified by CAS 156052-68-5, molecular formula C₁₄H₁₆Cl₃NO₂, and nominal molecular weight 336.64 g/mol. Two physical grades are used in pharmaceutical manufacture: an internal model designation ZOX-VET-100 for solid-dosage and premix operations, and an internal model designation ZOX-VET-200 for micronized injectable-preparation work. The solid-dosage grade is controlled for bulk density between 0.35 g/mL and 0.55 g/mL and tapped density between 0.55 g/mL and 0.75 g/mL under USP <616> and Ph. Eur. 2.9.34. The injectable-preparation grade is micronized to a laser-diffraction D50 below 10 µm and D90 below 25 µm under ISO 13320:2020. The term “veterinary grade” as used here denotes reduced impurity burden, controlled particle size, and endotoxin monitoring required for pharmaceutical processing; it does not by itself establish a species-specific therapeutic indication or marketing authorization.

Because zoxamide lacks a harmonized compendial monograph in USP or Ph. Eur., the veterinary-grade release specification is an internal monograph supported by ICH Q3A(R2), ICH Q3C(R8), and ICH Q3D(R2). This differentiates it from compendial veterinary APIs such as ivermectin or amoxicillin trihydrate, for which public monograph attributes have been harmonized. Method validation follows ICH Q2(R2) and USP <1225>; specification limits are justified by process capability and, where available, toxicological data. Published data for some veterinary-specific zoxamide configurations are limited, and the absence of a monograph places final specification responsibility on the dosage-form manufacturer.

What Distinguishes Zoxamide Veterinary Grade API from Agricultural Technical Material?

The primary distinction between the veterinary-grade substance and zoxamide of technical or agricultural origin is the release specification and control of contaminants that are not addressed in crop-protection supply chains. Agricultural technical material may contain higher levels of homologous chlorinated impurities and is not routinely tested for bacterial endotoxins or objectionable microorganisms. The veterinary-grade API is released against a specification that includes bacterial endotoxins ≤0.50 EU/mg for injectable precursor lots by Ph. Eur. 2.6.14 or USP <85>, total aerobic microbial count ≤100 CFU/g, total combined yeasts and moulds ≤20 CFU/g for non-sterile solid-dosage-grade lots, and absence of Escherichia coli, Salmonella, and Pseudomonas aeruginosa per Ph. Eur. 5.1.4. Residual solvent content is controlled by USP <467> and Ph. Eur. 2.4.24, with the sum of Class 2 solvents typically limited to 0.5% w/w and individual Class 1 solvents not detected at 5 ppm or above depending on the solvent. Elemental impurities are screened by ICP-MS under USP <233>, with lead ≤1 µg/g, cadmium ≤1 µg/g, arsenic ≤2 µg/g, and mercury ≤0.5 µg/g as representative internal limits. The agricultural technical material is not routinely accompanied by a bacterial endotoxin certificate or by chromatographic related-substance profiles suitable for injectable dosage forms. This difference is critical when the same active entity is to be compounded into parenteral products rather than applied as a crop-protection spray.

Compared with broad-spectrum veterinary antibiotics and anthelmintic APIs, zoxamide has a narrow fungicidal mechanism involving inhibition of β-tubulin assembly and disruption of nuclear division in susceptible oomycete cells. This target selectivity reduces the likelihood of antibacterial cross-resistance but does not provide activity against common bacterial pathogens. The low aqueous solubility and high melting point of zoxamide further differentiate it from highly water-soluble veterinary APIs and direct formulation development toward non-aqueous vehicles, solid dispersions, or oral solids. The veterinary grade is not interchangeable with agricultural technical material because the agricultural supply chain does not apply pharmaceutical quality-system controls for pyrogens, microbial quality, elemental impurities, and consistent particle-size distribution.

Across tablet, capsule, powder, granule, and premix operations, the powder mechanical properties of the API often govern scale-up more than chemical potency. A needle-like crystal habit sometimes present in technical lots can promote punch filming and weight variation on rotary tablet presses operating at 60,000 tablets/h or above; the veterinary grade is therefore recrystallized and classified to reduce the needle fraction and improve flowability. Angle of repose is evaluated by USP <1174>, with an internal acceptance criterion below 40° for direct-compression blends. For capsule filling, a granular intermediate with tapped density 0.65 ± 0.05 g/mL and D90 below 150 µm is preferred because low-bulk-density micronized powder can create inconsistent slug formation on dosator-type machines. Premix processing is carried out in ribbon blenders or double-cone blenders with a controlled blending time of 10–20 min. Prolonged blending above 30 min can exacerbate segregation when the arithmetic difference in D50 between the API and excipient carrier exceeds 50 µm. Dry granulation may be used if the API is sensitive to residual moisture; wet granulation with a non-aqueous binder is acceptable only where the residual solvent programme can be completed within the established limit.

If Sterile Injection or Solution Forms Are Required, Solubility and Pyrogen Control Impose Narrower Operational Thresholds

Equilibrium water solubility of zoxamide is reported in the low mg/L range under OECD 105 conditions; published values in distilled water are generally below 10 mg/L at 20 °C, with some technical monographs indicating approximately 1 mg/L. Simple aqueous injectable solutions are therefore not technically feasible, and published formulation data for zoxamide in veterinary parenteral vehicles are limited. Sterile suspension or non-aqueous solution formats are the primary formulation routes. For suspensions intended for injection, the API is micronized to D50 ≤10 µm and D90 ≤25 µm and filtered through a 5 µm in-line filter during filling to reduce needle blockage. Non-aqueous vehicles must be dried to ≤0.1% w/w water because residual moisture above 0.3% w/w can alter suspension flocculation and increase microbial risk. Terminal sterilisation at 121 °C for 15 min is the default cycle only where forced-degradation data support stability; otherwise aseptic processing is required. Bacterial endotoxin control begins at the API stage with ≤0.50 EU/mg and is confirmed in the finished injection against the species-specific limit in the marketing authorization. Published thermal degradation data for zoxamide in sterile vehicles are limited; a forced degradation protocol at 40 °C / 75% RH and 60 °C dry heat for not less than 14 days should precede selection of the sterilization method.

Because the active substance has a high melting point near 159–161 °C determined by differential scanning calorimetry under ISO 11357-1, solid oral dosage forms tolerate short exposure to drying temperatures that would destabilize low-melting APIs. Fluid-bed drying of granules is typically performed at inlet air temperature 55–65 °C and dew point not exceeding −20 °C until loss on drying is below 1.5% w/w by USP <731>. Direct compression of the micronized injectable-preparation grade is not routinely used because cohesion increases as D90 falls below 25 µm; flow-aid addition with silicon dioxide at 0.2–0.5% w/w and magnesium stearate at 0.5–1.0% w/w may be necessary. Content uniformity is assessed by USP <905> and Ph. Eur. 2.9.40 using dosage units sampled from the beginning, middle, and end of the compression or filling run. If the granular intermediate segregates during transfer, the root cause is usually particle-size mismatch rather than assay loss; corrective action is to match the D50 of the granule and excipient within 50 µm. Open handling should be limited above 60% RH; surface moisture uptake can alter flow and require re-testing under Karl Fischer USP <921> before tabletting.

Residual Solvent Surveillance, Polymorph Identity, and Endotoxin Risk in Multi-Dosage-Form Manufacturing

Residual solvent surveillance is performed on every batch by headspace gas chromatography according to USP <467> and Ph. Eur. 2.4.24. The recrystallization solvent system is selected to exclude benzene, carbon tetrachloride, and 1,2-dichloroethane; method sensitivity for Class 1 solvents is established at 5 ppm or lower. Solid-state identity is confirmed by X-ray powder diffraction against the approved reference diffractogram under USP <941> and Ph. Eur. 2.9.33, because changes in crystalline habit can affect dissolution from tablets and physical stability of suspensions. Micronization may introduce localized amorphous content; the XRPD profile is therefore inspected for amorphous halo intensity relative to the crystalline reference. Endotoxin burden is not reduced by ordinary drying or particle-size reduction; it originates from microbial contamination and must be controlled at the pre-crystallization and equipment-cleaning stages. For oral solids and premixes, microbial quality is tested by membrane filtration or plate-count methods; for injectable intermediates, the pyrogen threshold controls the API release. Zoxamide is incompatible with strong oxidisers and strong mineral acids; prolonged contact with unprotected mild steel in wet processing should be avoided to prevent metal-catalyzed degradation. Storage is under tight closure at controlled room temperature 15–25 °C, protected from light and moisture, with retest intervals assigned only after long-term stability data under ICH Q1A(R2)-style conditions.

Table 2 lists the dosage-form conversion tests and corresponding standard designations used to release the API for specific formulations.

Precise control of residual moisture, particle size, and impurity burden is required because the same active substance may be exposed to dry blending, aqueous or non-aqueous granulation, and sterile filtration in a multiproduct facility. Cross-contamination risk is controlled by dedicated storage and by validated cleaning procedures, with acceptance limits for zoxamide residue set by toxicological or pharmacological activity data when available. If published data are limited for a specific species or route, the default cleaning limit is 10 ppm in the subsequent product or a calculated acceptable daily exposure. Published data for this specific veterinary configuration are limited for some sterilization and stability attributes, so each formulation should be supported by product-specific forced-degradation, container-closure, and endotoxin challenge studies. The solid-dosage, premix, and injectable-preparation grades are therefore released separately, with the injectable-preparation grade receiving the more restrictive endotoxin, water content, and related-substance controls.