Chlortetracycline Premix Veterinary Grade API is a fermentation-derived tetracycline antibiotic supplied as a yellow to golden crystalline powder, with the hydrochloride salt identified by CAS registry 64-72-2 and molar mass 515.34 g/mol. The free base corresponding to CAS 57-62-5 has molar mass 478.88 g/mol. The product is manufactured under veterinary active pharmaceutical ingredient controls aligned to 21 CFR 210 and 21 CFR 211 and is intended for downstream processing into tablets, injections, capsules, powders, granules, premix, and solutions. A single universal model designation does not exist; the manufacturer's model code typically combines a grade suffix for active content, particle size range, and sterile or non-sterile status. The certificate of analysis therefore carries the binding release values for assay, impurities, moisture, and residual solvents. The active entity is produced by fermentation of Streptomyces aureofaciens and is classified as a broad-spectrum tetracycline. In the United States, feed use is regulated as a Type A medicated article under 21 CFR 558.128. The 7-chloro substituent differentiates chlortetracycline from tetracycline and oxytetracycline and is responsible for a distinct photodegradation and moisture sensitivity profile. The product is not intended for human use and must be labeled as veterinary grade.

What Limits the Direct Compression Route for Chlortetracycline Hydrochloride in Low-Dose Tablets?

Direct compression of chlortetracycline hydrochloride is limited by its flow properties, segregation tendency, and sensitivity to moisture and light. On production-scale rotary tablet presses operated between 15 kN and 25 kN, low-dose tablets containing less than 10% active by weight generally require at least 70% by weight of a free-flowing diluent such as microcrystalline cellulose and dibasic calcium phosphate anhydrous to maintain acceptable weight variation. Content uniformity is evaluated by USP <905>; sampling should cover the beginning, middle, and end of the compression run because hopper discharge can segregate the active fraction by particle size. When residual granulation moisture exceeds 2.0%, sticking and surface mottling have been observed on production presses, and pre-drying at 40°C to 45°C in a fluid bed dryer is applied before compression. Light-protected compression rooms and amber polyethylene-lined drums reduce the formation of anhydro and epi degradation products that are not therapeutically equivalent to the parent molecule. Dry granulation by slugging or roller compaction may be necessary when the active fraction is higher than 15%, because direct compression may not provide sufficient flow without excessive levels of glidant.

For capsule filling and oral powder sachets, wet granulation with polyvinylpyrrolidone or pregelatinized starch is used to improve content uniformity and reduce dust. The drying step must remain at or below 45°C to limit epimerization. Capsule machines using dosator or tamping-pin units are set according to the tapped density and Carr index of the granulation; the fill weight is recalculated when the bulk density changes by more than 10% between API batches. Oral powders and granules for solution are packaged with silica gel and protected from light. A free-flowing granulate with median particle size between 100 μm and 300 μm by laser diffraction is generally preferred for rapid dispersion. Dissolution testing for tablets and capsules under USP <711> must be used to confirm release from the formulated batch. Alkaline fillers, carbonate salts, and highly buffered systems above pH 7.0 are avoided because the tetracycline ring degrades rapidly under alkaline conditions. When effervescent powders are formulated, the acid source should be separated from the active premix if free moisture is present, because local acid-catalyzed degradation can occur during storage.

Premix Carrier Homogeneity and Residual Moisture Control

In premix manufacture, chlortetracycline is geometrically diluted into carriers such as rice hulls, soybean meal, or calcium carbonate using a stainless steel ribbon blender or twin-shell blender. Blend uniformity is determined by high-performance liquid chromatography rather than visual inspection; a common release target is ±10% of declared activity across the finished premix, with regulatory alignment to 21 CFR 558.128. Mixing time should be established by a blend uniformity study, not a fixed default, because over-blending can induce electrostatic segregation of micronized active particles. Residual moisture in plant-based carriers should remain below 12%, and mineral carriers below 3%, because free moisture accelerates degradation to anhydrochlortetracycline. Sieve analysis of the carrier according to USP <786> or equivalent is required before scale-up; batch-to-batch variance is most often associated with differences in carrier particle size distribution and bulk density. The final premix is incorporated into complete feed or top-dressed feeds according to the species-specific label dose and withdrawal period. Production lines that handle ionophore anticoccidials should be dedicated or cleaned with validated procedures to prevent cross-contamination.

Chlortetracycline is not directly interchangeable with oxytetracycline or tetracycline in existing formulations. The 7-chloro substituent present in chlortetracycline changes the degradation profile and aqueous solubility; formulators should re-confirm blend homogeneity, dissolution, and impurity profile when substituting one tetracycline for another. Oxytetracycline contains a 5-hydroxy group and is frequently encountered in injectable dosage forms, whereas chlortetracycline is more commonly used in feed premixes and oral powders. Published rate constants for tetracycline degradation are often obtained under different pH, light, and temperature conditions; therefore direct numerical comparison without a defined test method is not appropriate. For medicated feed applications, the approved species and dose combinations under 21 CFR 558.128 are specific to chlortetracycline and should not be assumed to apply to other tetracyclines.

When Sterile Aqueous Injection Requires pH Control and Light Exclusion

Injectable formulations of chlortetracycline are constrained by the molecule's aqueous instability. If an aqueous solution is manufactured, the pH is adjusted to 2.5 to 3.5 with hydrochloric acid or a suitable acid buffer, and the solution is sparged with nitrogen before and during aseptic filling. Terminal autoclaving is generally avoided because thermal degradation products, including anhydrochlortetracycline and epi derivatives, may exceed monograph limits; sterile filtration through a 0.22 μm polyvinylidene fluoride or polyethersulfone membrane is preferred. The drug substance, container, and closure must all be sterile and pyrogen controlled according to USP <71> sterility and USP <85> bacterial endotoxin testing where applicable. Reconstituted oral solutions for drinking water medication should be used within 24 h and protected from light; published stability data for high-hardness or carbonate-alkaline drinking water are limited, and farm-level stability studies are required before administration. For non-aqueous injections, the API is suspended in an approved oil or glycol vehicle, and the finished product is tested for syringeability, viscosity, and sterility. The use of antioxidants and chelating agents should be evaluated because the degradation pathway involves metal-catalyzed degradation.

Quality control release requires identification, assay, related substances, water content, residue on ignition, heavy metals or elemental impurities, and microbial limits. Assay is expressed as chlortetracycline hydrochloride on the dried basis; the USP monograph acceptance value is not less than 900 μg/mg. The high-performance liquid chromatographic method uses a reversed-phase C18 column with an acidic mobile phase; detection is commonly performed at 280 nm. The method separates chlortetracycline from 4-epi-chlortetracycline, anhydrochlortetracycline, and 4-epi-anhydrochlortetracycline; acceptance limits are set by the current USP or Ph. Eur. monograph and are shown on the certificate of analysis. Loss on drying and water content are determined by USP <921>; the exact release value is part of the approved specification. Residual solvents are controlled according to VICH GL18, and the manufacturer must provide batch-specific data for solvents used in the final crystallization step. In addition, the API should be screened for particle size distribution by laser diffraction or sieve analysis, because the particle size influences blending, segregation, dissolution, and premix homogeneity.

Bulk powder specifications for the premix grade should include tapped density, bulk density, particle size distribution, and residual moisture. Bulk and tapped density are determined according to USP <616>; the values are batch-dependent and are reported on the certificate of analysis. A change in bulk density greater than 10% between API batches can shift capsule fill weight and premix scoop volume. Particle size distribution is controlled because overly fine API may create dust and poor flow, while overly coarse API may cause blend segregation; a typical controlled range for direct compression-grade material is 90% of particles below 200 μm, but the supplier's specification prevails. The user should set the tablet press, granulator, or blender parameters based on these physical values rather than relying on chemical potency alone.

Regulatory Classification Follows the Type A Medicated Article Route

Regulatory classification of this product in the United States follows the Type A medicated article route under 21 CFR 558.128. The regulation lists chlortetracycline as a permitted drug in feed for designated species and classes, with approved combinations and withdrawal periods. The API is not intended for human use and must be labeled as veterinary grade. Export and import requirements may include a certificate of analysis, certificate of origin, and documentation of compliance with the relevant pharmacopoeial monograph. In addition to feed applications, the API can be formulated into tablets, capsules, granules, powders, and solutions, but each finished dosage form must be registered according to the destination jurisdiction. The manufacturer's model or grade code should be cross-referenced with the Drug Master File or Veterinary Master File where available. Purchasers should verify that the product is manufactured under veterinary GMP and that the analytical methods are validated according to VICH GL2 or regional equivalent.

Commercial batches should be packaged in amber high-density polyethylene drums with polyethylene liners and stored at controlled room temperature below 25°C, protected from light and moisture. The shelf life is assigned by the manufacturer based on stability data generated according to VICH GL3 or regional equivalents. When the active premix is used in medicated feed, the mixer should be cleaned between batches to prevent cross-contamination with ionophore anticoccidials or other antibiotics; incompatibility with alkaline feed components, oxidizing agents, and strong metal-ion chelators should be assessed before batching. A process validation report should include blend uniformity, active recovery, degradation product levels, and final moisture content for at least three consecutive production batches. Published data for long-term stability of chlortetracycline in complete feed under high environmental temperature and humidity are limited; therefore, field stability monitoring at the point of use is recommended.