Pegloticase is a recombinant, PEGylated uricase enzyme used as a uric acid-lowering biologic for adults with chronic gout that remains inadequately controlled with conventional therapy. It is a complex biological active pharmaceutical ingredient, not a conventional small-molecule API. The substance is a PEG conjugate of recombinant modified mammalian urate oxidase (uricase) produced using a genetically modified strain of Escherichia coli.
Pegloticase is associated with the CAS Number 885051-90-1 and FDA UNII R581OT55EA. PubChem and NCBI classify it as a complex protein/PEG conjugate rather than a discrete small-molecule chemical structure.
The pharmaceutical product KRYSTEXXA contains pegloticase and is administered by intravenous infusion. The current U.S. labeling describes pegloticase as a uric acid-specific enzyme that catalyzes the oxidation of uric acid to allantoin, thereby lowering serum uric acid concentrations.
Pegloticase consists of recombinant uricase that is covalently conjugated to monomethoxypolyethylene glycol (mPEG). The current product description specifies 10 kDa mPEG. Each uricase subunit has an approximate molecular weight of 34 kDa, while the active pegloticase molecule is a tetrameric enzyme conjugated with PEG and has an average molecular weight of approximately 540 kDa.
Because pegloticase is a heterogeneous PEGylated protein, it should not be assigned a conventional fixed molecular formula such as those used for small-molecule APIs. Its molecular characteristics are better described through:
This distinction is important when preparing an accurate CMS product page.
Pegloticase works through an enzymatic mechanism that differs substantially from conventional gout medicines.
Uricase catalyzes the oxidation of uric acid to allantoin. Humans lack functional uricase, and uric acid is therefore the final product of purine metabolism. Allantoin is substantially more soluble than uric acid, allowing the body to eliminate the resulting metabolite more readily.
By enzymatically reducing circulating uric acid, pegloticase can produce substantial reductions in serum urate concentrations in appropriately selected patients.
The current KRYSTEXXA prescribing information identifies pegloticase as a uric acid-specific enzyme and describes its therapeutic effect through conversion of uric acid to allantoin.
PEGylation is a defining characteristic of pegloticase.
The uricase protein is covalently conjugated to 10 kDa monomethoxy polyethylene glycol. The PEG component increases the size of the biological molecule and contributes to its pharmacokinetic properties. The current label reports approximately 24 mg of 10 kDa mPEG associated with every 8 mg of uricase protein in the finished product.
The PEGylation degree is therefore an important critical quality attribute. Analytical characterization can include evaluation of:
Historical development documentation identifies mPEG/monomer, polymeric forms and product-related impurities among the active-substance specifications.
Pegloticase should not be assigned a single exact molecular weight in the same manner as a conventional API.
The current official product description provides:
Uricase subunit: approximately 34 kDa
mPEG: 10 kDa
Pegloticase average molecular weight: approximately 540 kDa
The approximately 540 kDa value represents the PEGylated tetrameric biological drug substance and is the most appropriate molecular-weight description for a CMS page.
Pegloticase is indicated for adults with chronic gout refractory to conventional treatment, where persistent hyperuricemia remains clinically problematic.
The FDA-approved product is administered intravenously. Current labeling also contains important safety information concerning infusion reactions, anaphylaxis and G6PD-associated hemolysis/methemoglobinemia.
Pegloticase therefore has pharmaceutical relevance in:
Unlike a conventional small-molecule API, the active-substance specification for pegloticase includes biological and protein-specific quality attributes.
The European Medicines Agency assessment report identifies active-substance tests covering:
This means that a CMS specification table for pegloticase should emphasize protein content, enzymatic potency, PEGylation, molecular-size distribution, impurities, endotoxin and microbiological quality rather than forcing conventional small-molecule fields such as melting point or residue on ignition.
The current KRYSTEXXA formulation expresses concentration in terms of uricase protein.
The traditional formulation contains 8 mg/mL pegloticase as uricase protein, with the uricase protein covalently conjugated to 24 mg of 10 kDa mPEG per mL.
A current ready-to-use formulation is also described as 8 mg/50 mL, corresponding to 0.16 mg/mL, while maintaining 8 mg of uricase protein per vial.
These are finished-product concentrations and should not automatically be treated as the release specification for bulk drug substance.
Analytical testing for pegloticase requires multiple orthogonal methods because the molecule contains both a recombinant protein component and PEG conjugates.
Potential analytical methods include:
FDA review documentation specifically discusses evaluation of enzymatic activity, monomer and high-molecular-weight forms by SEC-HPLC, peptide mapping for PEG-lysine site occupancy, and LC-MS peptide mapping for detecting over- and under-PEGylated species.
A historical provisional bulk PEG-uricase specification publicly available in a commercial agreement provides useful numerical reference information, including:
These values are identified in the source as provisional bulk PEG-uricase API specifications, not as a current universal pharmacopoeial monograph. Therefore, they should be labeled as reference/process-specific specifications in a CMS rather than presented as current pharmacopoeial limits.
Important critical quality attributes for Pegloticase API include:
These attributes are consistent with regulatory documentation describing pegloticase active-substance controls.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.1% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 0.5% |