Beta-cyclodextrin Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable is the native unsubstituted betadex grade, a cyclic oligosaccharide consisting of seven α-D-glucopyranose units linked by α-(1→4) glycosidic bonds. The molecular formula is C₄₂H₇₀O₃₅ and the molar mass is 1134.98 g/mol; the CAS registry number is 7585-39-9. The material is controlled as an active pharmaceutical ingredient-grade powder under ICH Q7, and the certificate of analysis is aligned with the current USP–NF Betadex monograph and the European Pharmacopoeia Betadex monograph. Identification is carried out by infrared absorption spectrophotometry and specific optical rotation; assay on the anhydrous basis is controlled between 98.0% and 101.0%. Water content by Karl Fischer is controlled at ≤14.0% w/w, reflecting the native crystalline hydrate. Sulfated ash is controlled at ≤0.1%. Residual solvent testing follows ICH Q3C, elemental impurities follow ICH Q3D and USP <232>/<233>, and microbiological quality is tested according to USP <61> and USP <62>.

The toroidal cavity has an internal diameter of 0.60–0.65 nm, an external diameter of 1.53 nm, and a cavity height of 0.79 nm. Aqueous solubility at 25°C is approximately 18.5 g/L; this value is lower than that of α-cyclodextrin because of intramolecular hydrogen bonding across the secondary hydroxyl rim. The cavity accommodates lipophilic guest molecules or moieties with molecular volume below the cavity cut-off, forming inclusion complexes with 1:1 or drug-dependent higher stoichiometries. Commercial oral complexes such as piroxicam–β-cyclodextrin have used a 1:2.5 molar ratio to control dissolution and gastric irritation. Complexation efficiency should be confirmed by phase-solubility studies, differential scanning calorimetry, powder X-ray diffraction, or nuclear magnetic resonance, because incomplete complexation can generate free crystalline drug and reduce tablet robustness.

Inclusion complex formation in aqueous media is commonly evaluated with the phase-solubility method described by Higuchi and Connors. An A_L-type profile indicates a 1:1 complex and an A_P-type profile indicates higher-order complexes. The apparent stability constant for β-cyclodextrin–drug complexes generally ranges from 10² M⁻¹ to 10⁴ M⁻¹, which is lower than that of some substituted cyclodextrins; this moderate affinity can be sufficient for oral dissolution enhancement but may be less effective for maintaining drug in solution after parenteral dilution. Differential scanning calorimetry can indicate inclusion by attenuation of the guest melting endotherm, while residual endotherms may indicate free crystalline drug. Powder X-ray diffraction can also discriminate between a physical mixture and an inclusion complex by the loss of guest crystallinity peaks. If these observations are absent, additional formulation-specific validation is required.

What Distinguishes Native Beta-Cyclodextrin from Substituted Cyclodextrins?

Substitution of the hydroxyl groups changes aqueous solubility, renal elimination, and formulation behaviour. Native β-cyclodextrin has 7 glucose units; α-cyclodextrin has 6 and a smaller cavity of 0.47–0.53 nm; γ-cyclodextrin has 8 and a larger cavity of 0.75–0.83 nm. Hydroxypropyl-β-cyclodextrin has water solubility above 600 g/L, while sulfobutyl ether-β-cyclodextrin sodium is anionic and has water solubility above 500 g/L. Native β-cyclodextrin is therefore not interchangeable with these derivatives in liquid injectable concentrates, because the dissolved carrier concentration required for sufficient drug solubilisation cannot be reached with the native material. In oral solid dosage forms, however, the crystalline nature and moderately low solubility of β-cyclodextrin become process advantages: the powder is dry, compressible after granulation, and does not show the surface tackiness observed with amorphous substituted cyclodextrins at elevated relative humidity.

The principal distinguishing property in tablet and capsule manufacturing is not cavity size but powder mechanical behaviour. Native β-cyclodextrin is crystalline and typically has a bulk density in the range 0.45–0.60 g/cm³ with a tapped density of 0.60–0.75 g/cm³; the resulting Carr index may exceed 20% and the angle of repose may be above 35°, indicating cohesive flow. A direct compression formulation containing more than 50% w/w β-cyclodextrin should therefore be evaluated on an instrumented rotary press with compaction force and ejection force monitoring; if tablet tensile strength or ejection force exceeds the press capability, dry granulation by roller compaction or wet granulation should be used. For capsule filling, low flowability makes volumetric dosing inconsistent unless the granulate is densified or a force-fed auger system is used.

The product grade is distinguished from technical cyclodextrin by reduced reducing sugar content and controlled related oligosaccharides. Reducing sugars are tested by a colorimetric method or liquid chromatography; unreacted starch hydrolysates and linear dextrins can act as nutrients for microbial growth and can affect tablet hardness. The pharma-grade recrystallised material has a narrower particle size distribution and lower endotoxin burden. If the powder is micronised to improve flow, the resulting increase in surface energy can raise adsorption of the active ingredient and make de-blending more likely in high-speed capsule filling. Any change in milling or drying should trigger re-validation of blend uniformity using USP <905> and dissolution using USP <711>.

Granulation, Compression, and Capsule Filling Boundaries

High-shear wet granulation of β-cyclodextrin with water or a binder solution is used to produce granules for tablets and capsules. The granulation endpoint should be controlled by impeller torque or power consumption rather than by fixed time. For a high-shear granulator with impeller tip speed in the range 4–8 m/s, water addition is typically stopped before the mass becomes paste-like; the exact amount is formulation-dependent, but over-wetting can occur when the addition exceeds 20–25% w/w in simple β-CD–lactose systems. After drying, the granules should be milled through a screen of 0.8–1.0 mm. Granule particle size distribution is measured by sieve analysis according to USP <786>. Tablet blend uniformity is assessed by USP <905>, and finished-tablet dissolution is assessed by USP <711> Apparatus 2 at 50–100 rpm in 900 mL medium; medium pH should be selected according to the active ingredient’s ionisation profile. Tabletability with β-cyclodextrin depends on residual moisture: overdried granules below 1.5% w/w moisture may increase capping tendency, whereas moisture above 3.0% w/w may cause picking and weight variation. A specification for granule water activity below 0.60 has been used to prevent microbial growth in sugar-free formulations.

In capsule filling, size 0 or 1 hard gelatin capsules are commonly used when the fill weight is in the range 300–500 mg. For β-cyclodextrin-containing powders, a dosator machine with insufficient compression may produce weight variation because the powder bed does not transmit force; low-force tamping pin settings or dosator dies with polished surfaces reduce sticking. Capsule shells containing β-cyclodextrin should be stored at 25°C or below and protected from humidity above 60% RH, because the native hydrate can release water into the shell at elevated relative humidity and cause embrittlement. Batch-to-batch particle size variability should be monitored in the raw material specification if direct compression is used without granulation. Liquid-filled capsules are not usually manufactured with native β-cyclodextrin because the low water solubility would produce suspensions with limited homogeneity.

For oral solid dosage forms, complex preparation methods include kneading, co-precipitation, spray-drying, and co-grinding. Kneading with a water–ethanol mixture can produce a paste that is dried and milled; the residual alcohol must be controlled under ICH Q3C. Spray-drying of β-cyclodextrin with a poorly water-soluble drug can produce a fast-dissolving amorphous or partially amorphous complex, but the process is sensitive to inlet temperature and feed rate. A laboratory spray dryer with inlet temperature 140–180°C and outlet temperature 70–90°C is a common starting point; exact parameters depend on the drug load and solvent system. Co-precipitation from ethanol–water or acetone–water can generate crystalline inclusion complexes, but large solvent use and residual solvent removal are technical barriers. Co-grinding in a ball mill at 400–600 rpm for 30–60 min with stainless-steel balls has been reported for some β-CD systems; the method is not universally applicable and may produce amorphous mixtures rather than true inclusion complexes. Tablet and capsule formulations should state the method of complex preparation, because it affects dissolution and stability.

Tablet compression developers should evaluate β-cyclodextrin-containing powders for compaction properties using an instrumented compaction simulator or a single-punch press. The Heckel yield pressure of native β-cyclodextrin is higher than that of plastic fillers but lower than that of brittle excipients; compression data from the raw material certificate of analysis are not sufficient to predict tabletability. A compaction profile at 50–150 MPa can identify capping tendencies. If the tablet tensile strength drops at higher compression forces, the formulation may require a deformable binder such as microcrystalline cellulose or copovidone. For orally dispersible tablets, a β-CD complex may improve palatability by masking bitter actives; however, the taste-masking effect is compound-specific and should be confirmed by sensory evaluation or electronic tongue data. Without these data, a claim of universal taste masking is not technically supported.

When the Injectable Route Is Considered: Solubility, Osmolality, and Renal Clearance Constraints

Injectable formulations based on native β-cyclodextrin are constrained by three factors: low aqueous solubility, complex dissociation on dilution, and renal handling. The solubility of the unsubstituted molecule is only 18.5 g/L at 25°C, so a 10% w/v aqueous β-cyclodextrin carrier cannot be prepared without supersaturation or heat. Upon intravenous administration, the complex can dissociate in plasma; the released lipophilic drug may precipitate locally if the volume of distribution is small, whereas the β-cyclodextrin fraction is cleared by glomerular filtration. Native β-cyclodextrin is known from toxicological studies to produce renal tubular vacuolation at high parenteral doses because the molecule can accumulate in the kidney; for this reason, substituted derivatives such as sulfobutyl ether-β-cyclodextrin and hydroxypropyl-β-cyclodextrin are generally selected for injectable products. If an injectable application is nevertheless specified, the formulation must demonstrate no visible particles under Ph. Eur. 2.9.20 or USP <788>, acceptable osmolality by USP <785>, and endotoxin control by USP <85>. Stability of the aqueous solution should include pH, subvisible particulate matter, and complexation efficiency after terminal sterilisation or aseptic filtration.

Terminal sterilisation of β-cyclodextrin solutions by autoclaving at 121°C for 15 min can be performed only after pH stability is established. In acidic conditions below pH 4, acid-catalysed hydrolysis of α-(1→4) glycosidic bonds accelerates at elevated temperature and can reduce assay below the pharmacopoeial limit. The solution should be buffered if the formulation pH is below 4 or above 8, and the fill volume should be adjusted to compensate for water loss during sterilisation. Aseptic filtration through a 0.22 µm sterilising grade membrane is an alternative only when the solution has a low bioburden and the active ingredient–β-cyclodextrin complex does not bind to the filter. The use of terminal sterilisation cycles outside the validated range requires additional degradation data for the guest molecule, because the inclusion complex does not necessarily protect all drugs from hydrolytic degradation.

The low water solubility of β-cyclodextrin can be increased by heating or by co-solvent addition, but the dissolved fraction may recrystallise upon cooling or dilution. In injectable formulation, co-solvents such as propylene glycol or ethanol may be used, but the total organic solvent load is limited by the route and by the active ingredient’s tolerability; no more than 10–20% v/v ethanol is common in parenteral formulations, and higher levels require clinical justification. β-cyclodextrin can bind to preservatives and reduce their antimicrobial activity; therefore preservative efficacy testing according to USP <51> should be performed if a multi-dose injectable product or oral liquid is developed. The complexation of benzalkonium chloride or parabens may lower the free preservative concentration below the minimum inhibitory concentration, so the total preservative content cannot be set by formula alone.

Stability testing for β-cyclodextrin raw material should be designed according to ICH Q1A(R2). The native hydrate is chemically stable in the dry state for 36 months when stored at 15–25°C and protected from humidity; re-evaluation intervals are based on the approved re-test period. At relative humidity above 60% RH, the powder can absorb moisture and the water content may exceed the monograph limit. The product should not be stored in contact with strong acids or oxidising agents at high temperature, because these conditions can hydrolyse or oxidise the glucose residues. If opened, the container should be re-closed under dry conditions and the remaining material retested for water content if the exposure exceeds 24 h.

For granules, β-cyclodextrin is often incorporated at 10–40% w/w in a dry blend before wet massing. The granulation can be used to improve the dissolution of poorly water-soluble drugs; the dissolution benefit is not guaranteed by β-cyclodextrin alone and must be demonstrated by comparative dissolution profiles against the uncomplexed drug. If the inclusion complex is prepared by kneading or co-precipitation, the molar ratio is selected from phase-solubility diagrams; a ratio that is too high can dilute the tablet and increase disintegration time, whereas a ratio that is too low leaves free crystalline drug. The disintegration time of β-cyclodextrin-containing tablets is typically evaluated with USP <701>; formulations with high β-cyclodextrin may require a disintegrant such as crospovidone or sodium starch glycolate at 2–5% w/w to maintain disintegration time below 15 min.

Batch release for the product includes appearance, identification, assay, related substances, water content, sulfated ash, specific optical rotation, residual solvents, elemental impurities, and microbial limits. The certificate of analysis should state the actual values against the pharmacopoeial acceptance criteria. For injectable use, additional release data include bacterial endotoxins, visible particles, sub-visible particulate matter, and sterility according to USP <71> after the formulation has been sterilised. The provided product specification is not a regulatory statement; each application must justify the grade, route of administration, and complexation ratio with its own stability and compatibility data.