Chlorhexidine Gluconate Solution (Lactating Cow) Veterinary Grade API for Tablets / Injections / Capsules / Powders / Granules / Premix / Solutions is supplied as a clear, colourless to pale-yellow aqueous concentrate. The commercial model designation CG-20-LC is assigned to the standardised 200 g/L chlorhexidine gluconate content, equivalent to 20% w/v. The solution has a density of 1.060–1.075 g/mL at 20 °C and a pH range of 5.5–7.0 when diluted 1:10 in carbon dioxide-free water. Identity is confirmed by infrared absorption and by retention time in the HPLC assay; the assay method uses a C18 column with ultraviolet detection at 239 nm. The product is released under veterinary GMP with batch-specific certificates of analysis covering appearance, assay, pH, density, related substances, and residue after evaporation. Storage in sealed high-density polyethylene drums at 15–25 °C, protected from light, maintains the assay within 19.0–21.0% w/v over the labelled shelf life. The lactating-cow designation indicates that the grade is supplied with bovine milk residue documentation, endotoxin screening where required for injectable development, and impurity control suitable for food-producing animal applications. The undiluted concentrate is free from added preservatives, dyes, perfumes, and anionic surface-active agents.

Why is a lactating-cow-specific grade required when the molecule is pharmacopoeial?

The lactating-cow designation reflects documentation and safety screening rather than a different molecular structure. Chlorhexidine gluconate from the same synthesis is a bis(biguanide) with molecular formula C22H30Cl2N10·2C6H12O7 and a molecular mass of 897.76 g/mol for the digluconate salt. The lactating-cow grade is released with lower acceptance limits for bacterial endotoxins—typically <0.5 EU/mg when tested according to Ph. Eur. 2.6.14—and with additional toxicological documentation concerning the 4-chloroaniline impurity, which is controlled to not more than 0.25% by area percent. In lactating dairy herds, the primary risk from teat and udder disinfection is not systemic absorption but carry-over of active material and degradation products into milk. The grade is therefore supplied with a solvent system that leaves negligible volatile residues under recommended drying times of 60–90 s before milking-unit attachment. Published data for the bovine milk transfer of chlorhexidine gluconate after intact-teat application are limited; therefore veterinary formulators are advised to verify the residue status against the target jurisdiction’s positive list before assigning a withdrawal period. The absence of added iodine, dyes, and short-chain alcohol co-solvents reduces the probability of off-odour and off-flavour carry-over into bulk tank milk.

Routine release data for CG-20-LC are generated using the following analytical methods. The concentration of 4-chloroaniline is measured by HPLC with an octadecylsilyl column, using a mobile phase of phosphoric acid and methanol with ultraviolet detection at 239 nm; the limit of quantification is 0.05%. Residue after evaporation is not more than 0.1% w/w, and the product is free from visible particulate matter when inspected against a black-and-white background. The compendial monograph also sets a total related-substances limit and a chloride-content limit that are recorded on the certificate of analysis. The solution is manufactured in dedicated stainless steel 316L equipment to avoid copper and iron contamination, which can accelerate oxidative darkening.

Residue-transfer boundaries, anionic incompatibilities, and solid-dose processing constraints

In solution products, dilution of the 200 g/L concentrate with potable water to 5–10 g/L chlorhexidine gluconate, or 0.5–1.0% w/v, is standard for post-milking teat disinfection. Anionic surfactants, natural soaps, sodium alginate, carboxymethylcellulose, and many bentonites form turbid precipitates or reduce free chlorhexidine concentration. Compatibility testing with a phase-separation protocol is required before finalising a premix or udder-wash formulation. In tablet and capsule manufacture, direct compression is not practical because the API is a viscous liquid. The concentrate is first adsorbed onto microcrystalline cellulose, dicalcium phosphate dihydrate, or maltodextrin at loading ratios of 10–25 wt%. High-shear granulation of the adsorbed powder with additional water must maintain product temperature below 30 °C to prevent tacky overwetting and dye transfer to punch faces. On a rotary tablet press fitted with 8 mm standard concave tooling, compression force is typically held at 8–12 kN; tablet hardness above 60 N may be achieved after drying at 40 °C for 2–3 h, but friability remains sensitive to residual moisture above 2.0%. Capsules containing the adsorbed powder are usually filled at 15–25 °C and below 45% RH to avoid softening of gelatin or hypromellose shells.

For aqueous injectables intended for local irrigation or topical instillation, bacterial endotoxin control and sterilisation by autoclaving at 121 °C for 15 min are possible only with adjustment to the final pH. Chlorhexidine gluconate degrades more rapidly above pH 8.0 and in the presence of trace transition-metal ions. Published data on its use as a systemic injectable in food-producing animals are limited; the product is therefore not assigned a systemic withdrawal period in bovine milk or meat. Solutions prepared for teat dipping should not be used as intramammary infusions unless specifically authorised in the target jurisdiction. The API is not suitable for combination with iodine-releasing compounds or anionic wetting agents because of immediate precipitation and loss of antimicrobial activity.

When the API is evaluated against povidone-iodine, quaternary ammonium compounds and hypochlorite

Comparative efficacy data under EN 1656:2019 for quantitative suspension tests in bovine milk soil show that chlorhexidine gluconate retains a > 5 log10 reduction against Staphylococcus aureus and Escherichia coli at 0.5% w/v after 5 min contact. Povidone-iodine at 1% w/v available iodine often shows equivalent immediate kill but loses activity in the presence of whey protein and milk fat. Hypochlorite solutions require higher free chlorine and are corrosive to milking equipment. Unlike iodine-based dips, chlorhexidine gluconate does not impart iodophor residues to bulk tank milk, and it does not stain the teat or operator skin. Compared with quaternary ammonium compounds, chlorhexidine gluconate has a faster kill against Gram-positive mastitis pathogens but is less effective against bacterial spores and some Pseudomonas spp.; quaternary ammonium compounds remain active at lower concentrations but are more readily neutralised by organic matter. The residual skin substantivity of chlorhexidine gluconate is reported at 6–8 h on cleaned teat skin, which supports its use as a post-milking barrier disinfectant rather than a pre-milking wash alone.

From a pharmaceutical manufacturability standpoint, the product differs from chlorhexidine hydrochloride or acetate powders because it is a ready-to-use liquid with a defined gluconate counterion. The gluconate salt avoids the use of hydrochloride in liquid formulations where chloride can contribute to stainless-steel pitting at concentrations above 200 mg/L. The 20% concentrate, however, requires liquid metering pumps rather than screw feeders. In medicated premix operations, a metering pump calibrated at 10–50 mL/min is used to spray the concentrate onto a moving carrier bed, while the mixer is purged with low-humidity air at 20–25 °C. Batch-to-batch variability in viscosity of the concentrated solution is typically ± 5%, which can influence spray nozzle droplet size distribution. Viscosity is therefore controlled at 50–80 mPa·s at 20 °C by dilution or temperature adjustment. Granules prepared with lactose monohydrate or corn starch may exhibit delayed disintegration if the chlorhexidine loading exceeds 15 wt%; dissolution testing under Ph. Eur. 2.9.3 or USP dissolution apparatus 2 is used to detect delayed release in the final product.

Published data for the specific configuration of chlorhexidine gluconate in lactating-cow injectable or intramammary formulations are limited. Most peer-reviewed studies address teat disinfection and dermal antisepsis rather than systemic or intramammary pharmacokinetics. Consequently, product-development work with this API for injections must include dedicated tissue-irritation, milk-residue, and ototoxicity studies before any clinical use claim is made. The absence of a general maximum residue limit for chlorhexidine in bovine milk in all jurisdictions further requires that the manufacturer confirm the regulatory residue status in each target market.

Long-term stability of the unformulated concentrate is supported by storage in 5 kg, 25 kg, and 200 kg high-density polyethylene drums with tamper-evident closures. Each drum is labelled with batch number, production date, retest date, and storage condition 15–25 °C. Unopened drums stored protected from light retain the assay within 19.0–21.0% w/v for 24 months from release. After first opening, the concentrate should be used within 90 days and the closure resealed under nitrogen or dry air to minimise oxidative darkening. Operators handling the concentrate should use chemical-resistant gloves and eye protection, because the undiluted liquid is a skin and eye irritant; spills are neutralised with dilute cationic surfactant solutions and copious water. No additional chemical stabilisers are required for the unformulated concentrate when stored as recommended.