Chorionic gonadotrophin, human chorionic gonadotrophin, is a heterodimeric glycoprotein with a molecular mass of approximately 36,700 Da. The alpha subunit contains 92 amino acids and two N-linked glycosylation sites at Asn52 and Asn78; the beta subunit contains 145 amino acids, two N-linked sites at Asn13 and Asn30, and four O-linked glycosylation sites on the carboxyl-terminal peptide. For injectable use, the API is compounded into a sterile lyophilized powder because the native conformation is not retained in ready-to-use aqueous solution at 25 °C. A typical vial labeled 5,000 IU or 10,000 IU contains the API, mannitol or lactose monohydrate as a lyoprotectant and bulking agent, and sodium phosphate or phosphate-citrate buffer to target a pre-lyophilization pH of 6.0–7.0. The manufacturing sequence starts with dissolution of the drug substance at 2–8 °C, followed by sterile filtration through a 0.22 µm PVDF or PES membrane. The filtered bulk is filled into Type I borosilicate glass vials under ISO Class 5 laminar airflow and partially stoppered with bromobutyl closures. After loading onto temperature-controlled shelves, the product is frozen to −40 °C to −45 °C at a ramp of 0.5–1.0 °C/min. Primary drying is conducted at a product temperature below the collapse temperature determined by freeze-drying microscopy; the chamber pressure is maintained at 0.18–0.25 mbar. Secondary drying is ramped to 25–30 °C until the residual moisture content is not more than 2.0–3.0% by Karl Fischer titration.

The lyophilization step is the primary process conflict. If the frozen product temperature crosses the collapse threshold, the drying matrix collapses, sublimation rate decreases, and reconstitution time lengthens; if the shelf temperature is held too low to avoid collapse, the primary drying phase extends beyond 48 h, increasing the time-dependent exposure of the glycoprotein to an amorphous frozen matrix. The dried cake is inspected for shrinkage, meltback, and cracking. Batch-to-batch variation in reconstitution time and subvisible particles is monitored after reconstitution with sterile water for injection. Sterility is assessed by USP 71, bacterial endotoxins by USP 85, particulate matter by USP 788, and potency by a biological assay calibrated against the WHO International Standard for human chorionic gonadotrophin. Residual moisture is measured by USP 921 Method Ic. The injection is used in ovulation induction and assisted reproductive technology protocols, where the labeled potency must be delivered after reconstitution; therefore the lyophilization cycle, closure integrity, and cold-chain storage at 2–8 °C are treated as critical process parameters rather than routine packaging details.

What Limits the Aqueous Storage Window for Compounded HCG Solutions?

Once lyophilized HCG is reconstituted in a hospital pharmacy or clinic, the aqueous solution is exposed to hydrolysis, deamidation, subunit dissociation, and agitation-induced aggregation. The pH of the reconstituted solution is maintained between 6.0 and 7.0 because the glycoprotein carries a net negative charge at formulation pH and is less prone to electrostatic aggregation than at its isoelectric point. If sterile water for injection is used, the solution is preservative-free and the beyond-use date assigned under USP 797 is conservative; if bacteriostatic water containing 0.9% benzyl alcohol is used, the preservative provides some protection against microbial growth, but the chemical stability of the peptide is not extended beyond the labeled beyond-use date. Subvisible particle formation after reconstitution is assessed by light obscuration and by visual inspection according to USP 790. The solution should not be shaken; gentle swirling is used to dissolve the cake because interfacial stress at the air-liquid surface can unfold the protein and generate aggregates that exceed the 10 µm and 25 µm particle thresholds accepted for small-volume parenterals.

Temperature is the dominant kinetic factor. At 2–8 °C, deamidation and oxidation are slowed but not stopped; at 25 °C, potency loss may be measurable within 24 h, and the rate increases further in non-buffered normal saline. Published data for this specific configuration is limited; therefore, compounding logs should record the time of reconstitution, diluent lot, storage temperature, and visual inspection result. For a 5,000 IU vial reconstituted to 500–1,000 IU/mL, the injection volume is calculated from the prescribed dose and the labeled potency per mL. The use of a closed-system transfer device is recommended where repeated withdrawals from a single vial are required, because repeated needle punctures increase the risk of microbial ingress and pressure variation.

When HCG Is Dispersed Into Oral Solid Dosage Matrices

Oral tablet and capsule development with HCG is constrained by gastric acidity, intestinal lumen proteases, and the molecular size of the hormone. The API has a molecular mass of approximately 36,700 Da and is not passively permeable in the jejunum at clinically relevant rates. Published data for this specific configuration is limited; therefore oral HCG presentations are not described in the current pharmacopoeial monographs and must be treated as experimental solid-dose formulations. Direct compression of HCG with microcrystalline cellulose, dibasic calcium phosphate dihydrate, or mannitol is conducted at low compression force, typically below 8 kN, because the low unit mass of the active component increases sensitivity to over-lubrication and capping. If the unit dose corresponds to less than 2 mg of active peptide, geometric dilution and pre-blending with a micronized filler are required to achieve an acceptance value of ≤15.0 under USP 905. USP 711 dissolution testing is performed with Apparatus II at 50 rpm, but the medium must avoid high surfactant concentrations that denature the glycoprotein; dissolution samples should be assayed by size-exclusion HPLC or a receptor-binding bioassay in parallel with immunoassay because chromatographic fragments may retain immunoreactivity but not in vivo bioactivity.

Enteric coating with Eudragit L 100-55 or hypromellose acetate succinate is applied to delay release until the pH exceeds 5.5, but enteric protection alone does not prevent trypsin or chymotrypsin degradation after gastric emptying. Permeation enhancers such as sodium caprate and salcaprozate sodium are used experimentally to increase transcellular uptake, yet these excipients can alter membrane integrity and may reduce HCG potency during prolonged contact in the solid matrix. The drying step after coating or granulation must keep product temperature below 40 °C; higher temperatures accelerate deamidation and subunit dissociation. Moisture protection is critical because the lyophilized API is hygroscopic and can become sticky during capsule filling; relative humidity in the processing suite is maintained below 40% RH. Capsule filling using a dosator or tamping pin machine is preferred over high-shear wet granulation unless the wet binder is added at 2–8 °C and the granulate is dried by vacuum or lyophilization rather than fluid-bed drying.

Granule and Unit-Dose Powder Uniformity for Microgram-Scale Glycoprotein Loading

Granulation of HCG for oral sachets, sublingual powders, or dry syrup formulations is performed by dry granulation because aqueous granulation creates a mobile environment for hydrolysis and oxidation. Roller compaction is used with a roll pressure selected to give a ribbon density that retains the active fraction inside the intragranular pores; the milled fraction is sieved to remove fines below 75 µm, which often contain a disproportionate share of active material due to the friability of the lyophilized peptide. The granulation is blended with colloidal silicon dioxide at 0.5–1.0% and sodium stearyl fumarate at 0.5–1.0% to improve flow and reduce picking. Blend uniformity is confirmed by stratified sampling and immunoassay because mass-based uniformity under USP 905 may fail to detect segregation of the low-dose peptide. The granules are filled into aluminium foil sachets with desiccant and stored at or below 25 °C; moisture ingress above 3.0% residual moisture increases particle agglomeration and reduces dissolution rate.

For sublingual delivery, the granule matrix must disintegrate within 5 min in 2 mL of artificial saliva. Crospovidone or crosscarmellose sodium is included at 2–5% to enable rapid wetting, but high levels of sorbitol or xylitol can create a hyperosmotic matrix that destabilizes the glycoprotein and causes a bitter or irritant effect. The particle size distribution is tested by sieve analysis according to USP 786 and the moisture content by Karl Fischer titration. The oral granule form is limited to product formats where local oromucosal research has been conducted; it is not interchangeable with the injected lyophilized presentation. Published data for this specific configuration is limited.

Diluent Chemistry Dictates the Post-Reconstitution Beyond-Use Date and Subcutaneous Injection Volume

HCG injection is reconstituted with sterile water for injection when immediate use is required, or with bacteriostatic water for injection when a multi-dose parenteral preparation is permitted by the national regulatory authority and the manufacturer's labeling. The reconstitution volume for a 10,000 IU vial is typically 10 mL if the final concentration is 1,000 IU/mL; for subcutaneous injection, volumes above 1.0 mL are avoided to reduce injection-site pain and variability in absorption. The osmolality of the reconstituted solution is contributed by the bulking agent; mannitol-containing formulations may be hyperosmotic, and this is documented in the package insert as a local injection consideration. The diluent is injected slowly down the inner wall of the vial, and the vial is swirled gently until the cake dissolves; shaking is contraindicated because it introduces foam and increases subvisible particle counts. The drug is then drawn through a 21–25 G needle for intramuscular use or a 25–31 G needle for subcutaneous use.

After reconstitution, the solution should be inspected for visible particles and discoloration. If a preservative-free diluent is used, the product is treated as a single-dose preparation and administered immediately; if bacteriostatic water is used, the vial is labeled with the beyond-use date assigned under USP 797. The dose is not diluted in intravenous solutions because HCG is not approved for intravenous administration and the low pH of some infusion fluids can precipitate or unfold the glycoprotein. Syringe selection matters because silicone oil from the syringe barrel can adsorb the peptide and reduce the delivered dose; low-silicone or silicone-free syringes are preferred when available. The delivery system is qualified by the device manufacturer using ISO 7886-1 and ISO 11608 standards for needles and injection systems. The target is to preserve the labeled potency through the time of injection, not merely at release.

The liquid prefilled syringe and cartridge formats present a boundary condition for HCG because the protein is exposed to the syringe barrel, silicone oil, and air bubble for the entire shelf life. Unlike low-molecular-weight heparin or insulin glargine, HCG does not retain a stable monomeric conformation in a ready-to-use liquid at 2–8 °C for multi-month storage. Subvisible particle counts measured by light obscuration after 24 h of agitated storage at 25 °C may exceed the limits of USP 788 for small-volume parenterals. The beta subunit is prone to adsorption at hydrophobic surfaces, and silicone oil droplets can act as nucleation centres for irreversible aggregation. If a liquid HCG injection is required, a dual-chamber device or a vial with separate diluent syringe is used, so the lyophilized powder and diluent remain separated until the point of administration. The drug product retains the stability attributes of the freeze-dried cake while the device allows patient self-administration. The dual-chamber system is assembled in a barrier isolator, and the API chamber is sealed with a bromobutyl plunger tested for moisture vapour transmission; the diluent chamber contains sterile water for injection or bacteriostatic water.

The development of a stable liquid HCG injection requires the addition of a surface-active stabilizer such as polysorbate 20 at 0.005–0.02% or poloxamer 188 at 0.1–0.5%, but these excipients can alter the size-exclusion HPLC profile and increase the risk of oxidative damage if peroxide impurities are not controlled. The formulation is characterised by dynamic light scattering for hydrodynamic radius, by micro-flow imaging for subvisible particles, and by reversed-phase HPLC for oxidized species. The operational boundary is that the liquid formulation must be refrigerated, protected from light, and not autoclaved after sterile filtration. Terminal sterilization by moist heat is incompatible with peptide structure; sterile filtration through a 0.22 µm membrane is the standard method. The final product is examined for closure integrity under USP 1207 and package integrity under ISO 11607-1. The injectable and oral presentations share the same API quality standard, but each downstream format requires separate stability studies and process validation.