Pregnant Mare Serum (PMS) Veterinary Grade API, also designated equine chorionic gonadotropin (eCG), is supplied under model code PMS-VET-API-LYO for lyophilized powder and PMS-VET-API-LIQ for liquid processing. The active substance is a glycoprotein hormone isolated from equine serum and standardized by in vivo bioassay to an International Unit potency against the relevant pharmacopoeial reference preparation. Its molecular mass is approximately 70 kDa. The API is intended for downstream manufacture of sterile injectables, tablets, capsules, powders, granules, premixes, and solutions used in veterinary reproduction management. The native molecule contains both FSH-like and LH-like activity within a single highly sialylated glycoprotein, which extends plasma residence time after subcutaneous or intramuscular administration relative to pituitary FSH preparations.

The lyophilized model is intended for sterile injectable and oral solid dosage forms; the liquid model is intended for ready-to-inject or further diluted solution manufacture. Both models are derived from pooled serum collected from healthy donor mares under veterinary supervision and are released only after serological screening for equine infectious anaemia and microbial contamination. This screening, together with downstream chromatographic purification, reduces batch-to-batch variance observed with crude serum-derived preparations.

What Release Tests Apply to PMS-VET-API-LYO and PMS-VET-API-LIQ?

Release specifications for both model codes are aligned with Ph. Eur. monograph 0719 for equine serum gonadotrophin for veterinary use. Potency is expressed in International Units per milligram or per millilitre and is assigned by comparative in vivo bioassay. The lyophilized grade is released as a white to off-white powder or cake with moisture content not more than 3.0% by Karl Fischer titration and reconstitution time below 2 min in Water for Injection at 20–25°C. The liquid grade is released as a clear to slightly opalescent solution at 500 IU/mL or 1000 IU/mL, depending on order configuration. Both grades are controlled for pH 6.0–7.5 and bacterial endotoxins. Residual solvent levels are controlled per ICH Q3C for the lyophilized grade. The non-sterile powder grade has a bioburden limit of not more than 100 CFU/g; the sterile injectable grade is filtered through a 0.22 µm membrane at the finished product stage.

Because potency is defined by in vivo bioassay, a 1% change in reference standard dilution can shift the labelled International Unit assignment. The release bioassay uses groups of immature female rats or mice with ovarian or uterine weight endpoints, and the pharmacopoeial statistical design requires bracketing of at least two dose levels of the sample against the standard. This is a recognized limitation of serum-derived gonadotropin standardization and explains why HPLC purity values alone are not sufficient for batch release.

Product differentiation from human chorionic gonadotropin (hCG) and pituitary FSH is defined by receptor-binding profile and sialic acid content. eCG binds both FSH and LH receptors and drives follicular recruitment followed by ovulation. hCG is predominantly LH-active and is used for ovulation induction or luteal support. Pituitary FSH is primarily FSH-active and requires repeated administration because of shorter half-life. eCG has a reported elimination half-life in ruminants of 40–50 h; pituitary FSH preparations are cleared within 2–5 h after intravenous administration. This difference permits single-dose eCG protocols in superovulation but also creates a narrower margin for overtreatment because prolonged luteal activity can occur when overdosed.

Compared with recombinant FSH, serum-derived eCG contains residual host proteins that are controlled by purification but cannot be reduced to zero. This creates a documented immunogenicity risk after repeated cycles in the same animal. However, recombinant FSH products are not approved for all veterinary species, and eCG remains the standard single-dose intervention for timed artificial insemination in pigs, sheep, goats, and cattle. The choice between eCG, hCG, and pituitary FSH should be based on the physiological action required and the species-specific protocol, not solely on International Unit potency.

Sterile Injectable and Solution Processing

Injectable products are prepared from PMS-VET-API-LYO by reconstitution in Water for Injection containing buffering salts and a bulking agent such as mannitol at 2–5% w/v. The solution is pre-filtered through a 0.45 µm membrane and then passed through a 0.22 µm sterilizing-grade membrane, filled into depyrogenated borosilicate glass vials under ISO 14644-1 Class 5 conditions, and lyophilized. Typical lyophilization parameters include a freezing ramp to −35°C at 0.5°C/min, primary drying at chamber pressure 0.2 mbar, and shelf temperature increase to +20°C for secondary drying. Terminal steam sterilization is not used because eCG is a heat-labile glycoprotein; liquid formulations require storage at 2–8°C and protection from light.

On commercial filling lines, batch-to-batch variance is managed by pre-filtration bioburden monitoring and post-fill potency testing. Silicone tubing and piston-seal elastomers should be tested for leached silicone oil because hydrophobic surfaces can promote eCG aggregation. The aqueous solution should not be mixed with amine-based buffers or high-ionic-strength phosphate above 100 mM without stability data. Liquid ready-to-inject formulations must not be frozen; freezing causes conformational aggregation and should be avoided. In-use stability for multi-dose vials is established at 28 days after first puncture unless a longer period is supported by an internal study.

Finished injectables are tested for subvisible particles per Ph. Eur. 2.9.19; the compendial small-volume parenteral limit is 6000 particles per container at 10 µm and 600 per container at 25 µm. Light obscuration should be performed after gentle swirling, not after vigorous shaking, because air bubbles and aggregated glycoprotein produce false-positive excursions. Filtration flux decline across the sterilizing-grade membrane is monitored as a process trend; a drop greater than 30% from the initial flux at constant pressure indicates filter fouling by aggregates.

Production-scale freeze-drying presents a shelf-temperature edge effect: vials located near the condenser line can retain higher residual moisture than center vials, leading to within-batch variability of up to 0.5% w/w. Transfer lines should be short and jacketed at 2–8°C to limit hold time below 6 h. Peristaltic pump fill speeds below 120 vials/min with 1.5 mm internal diameter silicone tubing have shown fewer subvisible particle excursions than higher-shear rotary piston lines. These observations are based on manufacturing-line behaviour for protein lyophilizates and should be confirmed for each specific eCG formulation.

When Oral Dosage Forms Are Specified for eCG-Based Products

Tablets, capsules, powders, granules, and premixes containing PMS-VET-API-LYO are not bioequivalent to injectables because the 70 kDa glycoprotein undergoes gastric hydrolysis and intestinal protease degradation. If oral administration is required for a specific protocol, the API should be blended under anhydrous conditions and protected by enteric coating. Direct compression is performed at moisture content below 2.0% and compaction force below 12 kN to reduce shear-induced aggregation. Fluid-bed granulation should maintain inlet air temperature not exceeding 35°C and product temperature below 28°C. Capsule filling of enteric-coated pellets requires a controlled-release dissolution test, and premix for feed or drinking water should be diluted to 0.1–1.0% w/w carrier.

Enteric coatings based on methacrylic acid copolymer should dissolve above pH 5.5 to target jejunal release; however, gastric pH in monogastric species may remain below 3.0 for 2–4 h after feed intake. This creates a narrow processing window: undercoating leads to acid denaturation, while overcoating delays release beyond the intestinal transit window. The solid dosage form should be packaged in aluminium-aluminium blisters with desiccant because residual moisture above 2.0% accelerates aggregation and loss of potency. Published data on systemic bioavailability after oral administration is limited; therefore, injectable dosage forms remain the standard for systemic reproductive management.

Granulation endpoint for eCG oral premix is best controlled by near-infrared moisture rather than time only. Fluid-bed dryers with bottom spray produce less API loss than top spray due to reduced cyclone carry-over; material loss in top spray units can exceed 2.0% when particle size is below 50 µm. Blending in stainless steel V-blenders should avoid intensifier bars above 150 rpm to limit electrostatic aggregation.

For estrus induction in sows, the injectable solution is administered as a single intramuscular dose of 400–1000 IU after progestagen withdrawal; ovulation is expected 40–48 h post-treatment. In sheep and goats, superovulation protocols commonly use 200–600 IU in combination with progestagen sponge removal and prostaglandin administration. In anoestrous cattle, 250–500 IU is used to stimulate ovarian cyclicity. Multi-dose vials containing preservative should not be autoclaved and must be discarded after 28 days of first puncture unless an in-use stability study supports a longer period. The API should not be combined with oxidising agents or strong alkaline solutions.

Pharmacopoeial batch release is not limited to potency; identity is confirmed by isoelectric focusing and peptide mapping. The manufacturer should specify host serum protein content because repeated administration of heterologous glycoproteins can elicit anti-eCG antibodies. This immunogenic response may reduce efficacy after repeated cycles in the same animal and is a documented limitation of serum-derived gonadotropins compared with recombinant products. Residual moisture in the lyophilized cake above 3.0% has been associated with potency decline during storage at 25°C.