Pharmaceutical-grade cabozantinib for tablet, capsule, granule, and injectable finished-dose manufacture is supplied as cabozantinib (S)-malate, a white to off-white crystalline solid with the molecular formula C28H24FN3O5·C4H6O5 and a molecular weight of 635.6 g/mol. The S-malate salt is identified by CAS 1140909-48-3; the free base is identified by CAS 849217-68-1. The compound is a multi-kinase inhibitor associated with inhibition of MET, VEGFR2, and AXL receptor tyrosine kinases. The API series is separated into direct-compression tablet grade, capsule-fill grade, dry/wet-granulation grade, and low-endotoxin sterile injectable grade. The active moiety is the same across the series; the grades differ in physical particle size, microbial quality, residual solvent profile, and packaging configuration. All grades are produced under ICH Q7 conditions, and release documentation includes certificate of analysis, lot number, retest or expiry period, and quality statements for residual solvents, elemental impurities, and, where relevant, sterility and endotoxin.

Approved oral solid strengths include 20 mg, 40 mg, and 60 mg tablets and 20 mg and 80 mg capsules; the injectable grade supports parenteral formulation development where dissolution and oil/water partition are not the primary absorption barriers. Because cabozantinib free base has low aqueous solubility, oral grades are micronized to increase dissolution surface area. The product is not a simple mixture but a defined salt; the counterion ratio is controlled by HPLC, and the crystalline form is confirmed by X-ray powder diffraction. Tablet, capsule, and granule applications use the same active moiety but require separate particle size and powder flow specifications because content uniformity and dissolution are sensitive to D90 and specific surface area.

What solid-state controls differentiate the tablet grade from the injectable grade?

Polymorphic identity is the first critical control. XRPD with Cu Kα radiation confirms the reference crystalline form; differential scanning calorimetry and thermogravimetric analysis detect solvates and hydrates. The oral solid grade is routinely air-jet milled and released by laser diffraction according to USP <429>. A typical oral direct-compression release criterion is D90 ≤20 µm and D50 2–5 µm, but the limit is drug-product specific and is set by the dissolution profile. The injectable grade is either a sterile micronized solid with D90 ≤10 µm for suspension formulations or a sterile-filtered solution prepared from a higher-purity API. Identical HPLC retention time, IR spectrum, and XRPD pattern are required for both grades, but the injectable grade carries additional microbial and particulate controls that are not applied to oral solid grades.

Surface area and bulk density are controlled because milled cabozantinib tends to retain electrostatic charge. The micronized powder shows poor flow; preblending with colloidal silicon dioxide or a milled diluent is routinely used before encapsulation or compression. The particle size method is qualified by the manufacturer using a wet or dry dispersion module, and the acceptance range is verified with at least three batches to demonstrate lot-to-lot reproducibility. Published data for a universal particle size specification are limited because the D90 target depends on the formulation, the dissolution apparatus, and the drug product strength.

In tablet and capsule manufacture, the release specification is linked to the oral dosage form's dissolution and content uniformity. A tablet grade with D90 ≤20 µm may be appropriate for a direct-compression 20 mg tablet, while a capsule blend may tolerate a broader D90 if the capsule fill contains a wetting agent and a high-shear preblend. The physical specification is therefore not a single point value but a validated window; changing from one mill type to another, or from a dry dispersion laser method to a wet dispersion, requires revalidation of D90, D50, and D10 because the measurement bias can exceed 2 µm at the D50.

Dissolution is governed by particle size, not merely by salt solubility.

Cabozantinib S-malate exhibits pH-dependent solubility; its aqueous solubility is higher under acidic conditions and declines as pH rises. Dissolution testing in USP <711> apparatus II commonly uses 900 mL of 0.1 N hydrochloric acid or pH 4.5 acetate buffer containing 0.1–0.5% sodium lauryl sulfate to maintain sink conditions, though the final surfactant level is product-specific. The need for particle size control arises because the dissolution rate of a low-solubility BCS II compound is surface-area limited. When the D90 exceeds the qualified upper limit, dissolution slows and content uniformity can fail in low-dose tablet and capsule products. Conversely, over-micronization increases electrostatic adhesion and reduces flow, so the target is not the smallest possible size but a controlled D90 window.

In tablet formulation, high-shear wet granulation is generally avoided because the salt can disproportionate under aqueous alkaline granulating conditions. Dry granulation, direct compression, or nonaqueous granulation is preferred. If wet granulation is required, acidic buffer solutions or nonaqueous binders are used, and the granule is dried to a moisture endpoint below 0.5% to prevent sticking and punch filming. This limit is based on the S-malate salt's tendency to sorb surface water and on the observation that residual moisture above this range increases adhesion on rotary press tooling.

On an instrumented 16-station rotary tablet press at compression forces between 8 kN and 18 kN, batch records show that punch filming and sticking are minimized when the magnesium stearate level is kept at 0.5–1.0% w/w and the lubricant blend time is limited to 2–5 min. Over-lubrication creates a hydrophobic film on the granules and delays wetting, which is critical for a BCS II compound. For roller-compacted granules, roll force is typically in the range 5–15 kN/cm and the granulator screen is 1.0 mm. Fine fraction below 75 µm may be recycled at 30–50% of the blend mass. These processing ranges are not universal release specifications; they are qualified against tablet hardness, disintegration below 15 min, and the approved dissolution profile. Published data for other compression trains are limited, so each manufacturing line must validate its own parameters.

Capsule-fill operations are run at 35–40% RH. The micronized API acquires electrostatic charge; grounding of the dosator head and inert gas purge improve weight uniformity. Gelatin and HPMC capsule shells are conditioned according to supplier limits to avoid brittleness and deformation. For capsule strengths of 20 mg and 80 mg, the powder blend may contain a wetting agent such as sodium lauryl sulfate; the blend is not lubricated with excessive magnesium stearate because the hydrophobic film retards dissolution.

Table 1 provides an example specification matrix for the two principal API grades. The limits are typical for an ICH Q3A-aligned quality system and are adjusted for regional pharmacopoeial monographs and approved drug product dossiers.

When terminal sterilization is not applicable, aseptic API processing becomes a separate release pathway.

Because published data for terminal sterilization of dry cabozantinib S-malate are limited, the injectable grade is not released by dry-heat or moist-heat sterilization of the finished API unless specifically validated. For solution formulations, the API is dissolved, prefiltered through a 0.45 µm membrane, and sterile-filtered through a 0.22 µm sterilizing-grade membrane. Filter integrity is tested before and after filtration by bubble point or diffusive flow according to the filter manufacturer's criteria. For suspension formulations, low-bioburden micronized API is handled in Grade A/ISO 5 with a Grade B/ISO 7 background. Final containers are tested for sterility according to USP <71> and for bacterial endotoxins according to USP <85>. Endotoxin limit is determined by the maximum intended dose; a typical small-volume parenteral control is <0.5 EU/mg, but the final limit must be calculated from the clinical dosing schedule.

The injectable processing stream is sensitive to filter plugging if the API concentration approaches the solubility boundary. A prefilter is used to reduce particulate load, and the solution is held under controlled temperature to avoid crystallization. Environmental monitoring includes settle plates, contact plates, active air sampling, and particle counting to ISO 14644-1. Manual open transfer is replaced by closed single-use assemblies to reduce bioburden ingress. For lyophilized injectable presentations, the API is combined with cryoprotectants in a low-endotoxin process, filled, and lyophilized; the reconstituted solution must meet USP <788> particulate matter limits and the manufacturer's osmolality specification.

Residual solvent and elemental impurity control for the injectable grade is more restrictive than for the oral grade because the route of administration bypasses the gastrointestinal barrier. Residual solvents are limited according to ICH Q3C and USP <467>; elemental impurities are limited according to ICH Q3D and measured by ICP-MS using USP <232>/<233>. Genotoxic impurities are controlled under ICH M7 with a threshold of toxicological concern of 1.5 µg/day at the drug product level. Unknown impurities above 0.10% require qualification unless a lower notification threshold applies. For injectable use, extractables from the sterilizing filter and elastomeric closures are assessed because the API solution or suspension is in direct contact with these materials.

Comparative processing profile with other oral kinase inhibitor salts

Cabozantinib S-malate differs from sunitinib malate, sorafenib tosylate, and lenvatinib mesylate in salt form, molecular architecture, and solid-state handling. Cabozantinib contains a quinoline ether and cyclopropane-1,1-dicarboxamide motif; the cyclopropane-related intermediates are monitored as potential impurities. The (S)-malate salt has a defined counterion ratio, and its low aqueous solubility makes particle size a primary release parameter. In contrast, sunitinib is supplied as a malate salt of an indolin-2-one with different photostability and pH-solubility constraints; sorafenib is a tosylate salt with a diaryl urea structure that often requires solubility enhancement in the finished tablet; lenvatinib is a mesylate salt whose hygroscopicity requires stricter humidity control during dispensing. These differences affect the manufacturing line: cabozantinib granulation is more sensitive to wet-massing pH and over-lubrication than some other kinase inhibitor salts, while injectable cabozantinib is more sensitive to filter plugging due to its low solubility.

For a manufacturer, selecting between the direct-compression tablet grade, capsule grade, granule grade, and injectable grade should be based on the intended finished dosage form and the validated process, not on a single particle size value. A direct-compression grade is not suitable for sterile suspension use without reprocessing, and an injectable grade is not automatically suitable for direct compression if its D90 is below the target but its bulk density and electrostatic charge are outside the validated range. Each grade is released with a lot-specific certificate, and change control from one grade to another requires revalidation of content uniformity, dissolution, and, where applicable, sterility and endotoxin performance.