Cloprostenol Sodium, CAS 55028-72-3, is a synthetic 16-aryloxyprostaglandin F_2α analogue supplied as a pharmaceutical-grade active pharmaceutical ingredient for tablet, capsule, granule, oral liquid, and injectable manufacturing. The product designation is Cloprostenol Sodium Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable. The molecule is the sodium salt of (5Z)-7-[(1R,2R,3R,5S)-2-[(E)-4-(3-chlorophenoxy)-3-hydroxybut-1-enyl]-3,5-dihydroxycyclopentyl]hept-5-enoic acid, with molecular formula C₂₂H₂₈ClNaO₆ and relative molecular mass 446.90 g/mol. The sodium counterion confers aqueous solubility and permits direct formulation into phosphate-buffered injectable vehicles or aqueous granulation fluids, whereas the free acid form is practically insoluble in water and commonly requires organic cosolvent or cyclodextrin solubilisation. This API is not supplied as a sterile finished product. Finished-dose manufacturers apply terminal sterilisation or aseptic filling, depending on route and container closure configuration.

The material is normally released against route-specific specifications. For oral solid grade, particle-size distribution and residual solvent profile are controlled for low-dose blending; for injectable grade, bacterial endotoxins and bioburden are additional critical quality attributes. In tablet and capsule dosage forms, the API is incorporated as a low-dose active in immediate-release matrices; in granule presentations it is processed into intermediate granules for compaction or oral reconstitution. For injectable presentations, the sodium salt is dissolved in aqueous buffer and filled as a ready-to-use solution or processed into a sterile lyophilized cake. The actual dose strength, species, and route are defined by the finished-product marketing authorization; this product supplies only the drug substance. Representative release criteria are summarised in Table 1. Individual pharmacopoeial monograph requirements may differ, and manufacturer–customer agreements should define the final specification.

Table 1: Representative release specification matrix for Cloprostenol Sodium Pharma Grade API

The HPLC assay and related-substances method for cloprostenol sodium typically uses an octadecylsilane C₁₈ column with UV detection at 210 nm. Phosphate buffer and acetonitrile gradient elution at pH 3.0–4.0 suppresses carboxylate ionisation and resolves the 5-trans and 15-epimeric impurities. System suitability criteria usually include resolution between cloprostenol and 15-epi-cloprostenol not less than 1.5 and tailing factor not more than 2.0. Because the API is hygroscopic, water content by Karl Fischer titration should be performed immediately after opening the sampling container, and the sample should be protected from ambient humidity during weighing.

Bulk packaging is typically a double polyethylene bag inside an aluminium foil laminate bag with desiccant and nitrogen overlay. The outer fibre drum should carry temperature loggers. Stability data for the packaged API should follow ICH Q1A or VICH GL3 requirements, with long-term storage at 25 °C/60% RH and accelerated evaluation at 40 °C/75% RH. The manufacturer should assign a retest period based on assay, water content, and related substances trends.

What Limits Low-Dose Blend Uniformity in Tablet and Granule Dosage Forms?

Low-dose tablet and capsule manufacture of cloprostenol sodium presents a content-uniformity challenge because the luteolytic dose range is extremely low. Direct compression blends are typically prepared by geometric dilution of the active ingredient with lactose monohydrate or microcrystalline cellulose, followed by lubrication with magnesium stearate. Blend uniformity is evaluated according to USP <905>, and finished tablets should be tested for dissolution using USP <711> apparatus 2 at paddle speed 50 rpm. If granulation is used, dry granulation or non-aqueous wet granulation is preferred because cloprostenol sodium is hygroscopic and susceptible to pH-dependent degradation. When aqueous wet granulation is unavoidable, granulating fluid pH is maintained between 5.0 and 6.0 and drying inlet air temperature is limited to 50 °C. Over-lubrication with magnesium stearate above 1.0% w/w should be avoided because hydrophobic film formation can slow dissolution, particularly at low drug loading. Granule formulations typically include a disintegrant such as croscarmellose sodium at 2–5% w/w and a glidant such as colloidal silicon dioxide at 0.5% w/w to improve flow and disintegration.

Production-scale batches on rotary tablet presses require controlled relative humidity because moisture uptake above 60% RH may promote sticking and aggregation. If pre-drying is required, the API is dried in a vacuum tray dryer at 40 °C for 4–8 h under nitrogen. Blend segregation is a recognized failure mode when particle-size D₉₀ exceeds 100 µm and bulk-density differences between ingredients exceed 0.3 g/mL. Thus jet milling or spray drying is used to reduce API particle size before blending. On bin blenders of 50–500 L, charge levels are maintained at 50–70% of capacity with rotation at 10–15 rpm for 20–40 min; the exact endpoint is determined by blend uniformity sampling at multiple locations. For high-shear wet granulation, impeller speed 200–400 rpm and chopper speed 1500–3000 rpm are common, but over-granulation should be avoided because the low-dose API may be excluded from coarse granules. Dried granules should have moisture content ≤ 1.5% and pass through a 20-mesh sieve before lubrication. For hard capsules, the blended powder is filled into hard gelatin or HPMC capsules using tamping-pin dosator or auger fill equipment; fill weight variability and dissolution profiles are monitored during campaign scale-up.

Relative to other prostaglandin F_2α derivatives, cloprostenol sodium is selected for aqueous solid and liquid dosage forms because of its salt form and 16-(3-chlorophenoxy) substitution. The free acid is more lipophilic and may be preferred for non-aqueous semisolid intermediates; dinoprost tromethamine lacks the 16-(3-chlorophenoxy) substituent and is therefore subject to more rapid pulmonary oxidation by 15-hydroxyprostaglandin dehydrogenase. The substitution pattern also improves luteolytic potency per milligram in species such as cattle and swine, but quantitative dose reductions should be managed through bioavailability and regulatory equivalence studies rather than assumed from in vitro potency alone. Residual synthesis byproducts such as 3-chlorophenol and hydroxybutenyl intermediates must be controlled because they are not biologically equivalent to the active prostaglandin.

Table 2: Comparative formulation and metabolic properties of selected prostaglandin F_2α actives

Published data for specific cloprostenol sodium formulations are limited; therefore comparative pharmacokinetic performance should be confirmed by finished-dose in vivo studies under VICH GL52 or regional bioequivalence guidance. Analytical methods for related substances must resolve the 5-trans and 15-epimeric impurities because stereochemical inversion reduces biological activity.

When Cloprostenol Sodium Replaces Cloprostenol Free Acid or Dinoprost Tromethamine in Aseptic Injectable Filling

Injectable formulations of cloprostenol sodium are commonly compounded as sterile aqueous solutions, with pH buffered between 5.0 and 6.0 and tonicity adjusted with sodium chloride. The solution is filled through a 0.22 µm PVDF or polyethersulfone filter because the active molecule is heat-labile. Terminal moist-heat sterilisation at 121 °C for 15 min may be possible only if stability-indicating data demonstrate no more than 2.0% total related substances; otherwise aseptic filtration and barrier isolator filling under ISO 13408-1 are required. The container closure must protect against visible and ultraviolet light because the aromatic chlorophenoxy group absorbs below 300 nm and photodegradation can occur. Oral liquid formulations are buffered similarly and protected from light; oxidative degradation is limited by nitrogen sparging and addition of disodium edetate at 0.01–0.1% w/v.

Alternatively, lyophilized cloprostenol sodium formulations may be prepared by freeze-drying a buffered solution containing mannitol or trehalose as cryoprotectant at 3–5% w/v. A typical cycle includes primary drying at shelf temperature −30 °C and secondary drying at 25 °C, with the final cake monitored for moisture content and reconstitution time. Since the sodium salt is hygroscopic, the lyophilized cake requires sealed glass vials with low moisture transmission stoppers and residual moisture ≤ 1.0%.

Processing boundaries include storage below 25 °C in closed containers with desiccant because the sodium salt is hygroscopic. Exposure to relative humidity above 60% RH can induce aggregate formation and reduce assay. The sodium carboxylate is incompatible with strongly oxidising agents and with alkaline conditions above pH 8.0, where rapid degradation is expected. If aseptic filtration is used, filter compatibility testing under extractables and leachables protocols should be performed, and fill-volume uniformity should be verified across the campaign using in-process checks aligned with Ph. Eur. 2.9.17 or USP <698> for deliverable volume.