Paricalcitol API is a synthetic analog of vitamin D₂ and belongs to the vitamin D receptor agonist class. It is a potent active pharmaceutical ingredient used in the management of secondary hyperparathyroidism associated with chronic kidney disease. Paricalcitol is chemically identified as 19-nor-1α,25-dihydroxyvitamin D₂, with the molecular formula C₂₇H₄₄O₃, molecular weight 416.64 g/mol, and CAS Number 131918-61-1. PubChem confirms the molecular formula, molecular weight and CAS number, while FDA labeling identifies Paricalcitol as a synthetic analog of calcitriol.
Paricalcitol is a chiral seco-steroid molecule containing multiple defined stereocenters. Unlike conventional small-molecule APIs that may be supplied as racemates, the stereochemical configuration of Paricalcitol is an important part of its chemical identity. FDA CMC documentation describes the drug substance as a chiral molecule with multiple chiral centers and confirms that the drug substance meets USP compendial requirements.
USP 2025 defines Paricalcitol as containing 97.0–103.0% of C₂₇H₄₄O₃, calculated on the dried basis.
Paricalcitol is used as a vitamin D analog in pharmaceutical products intended to regulate parathyroid hormone levels. FDA labeling identifies Paricalcitol Injection for the prevention and treatment of secondary hyperparathyroidism associated with chronic kidney disease.
Applications include:
Paricalcitol is available in pharmaceutical injection products as a sterile aqueous solution containing Paricalcitol with suitable solvents. The USP Paricalcitol Injection monograph specifies 90.0–110.0% of the labeled amount of Paricalcitol.
Paricalcitol is structurally related to the active vitamin D hormone system. It is a synthetic vitamin D analog designed to provide vitamin D receptor activity while being used clinically in the management of secondary hyperparathyroidism.
The molecule has three oxygen atoms and a highly lipophilic seco-steroid structure. PubChem reports an XLogP3-AA value of approximately 5.0 and topological polar surface area of 60.7 Ų.
FDA CMC documentation describes Paricalcitol drug substance as a white to almost off-white powder and notes its limited water solubility of <0.05 mg/mL while being freely soluble in alcohol. The material is also sensitive to light and degradation under certain conditions.
The USP 2025 Paricalcitol monograph provides defined quality requirements for the API.
The principal numerical specifications include:
The USP assay uses liquid chromatography with UV detection at 252 nm. The current monograph specifies an L1 column, 2 mL/min flow rate and 100 µL injection volume.
Paricalcitol requires careful impurity monitoring because the molecule is sensitive to light and can undergo degradation. The USP impurity procedure specifically monitors 22Z-Paricalcitol and other individual impurities.
USP 2025 specifies:
The USP system-suitability procedure uses controlled UV exposure to generate 7Z-Paricalcitol and requires a resolution of NLT 1.5 between Paricalcitol and 7Z-Paricalcitol.
Paricalcitol API quality control can include:
USP specifies infrared identification and HPLC retention-time identification. The assay and impurity methods use UV detection at 252 nm.
Paricalcitol is a highly potent pharmaceutical substance and requires controlled handling. The USP monograph specifies preservation in tight, light-resistant containers, storage under argon, and storage in a freezer.
Important handling considerations include:
Paricalcitol Bulk API is used for pharmaceutical formulation and manufacturing applications, particularly for injectable vitamin D analog products. Procurement documentation should specify the exact API identity, CAS number, molecular formula, assay basis and stereochemical identity.
The API should be clearly distinguished from finished Paricalcitol Injection. The API specification is 97.0–103.0% on the dried basis, whereas the finished injection USP monograph uses a labeled-content specification of 90.0–110.0%.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 2.0% |
| Total Impurities | NMT 0.50% |
| Solubility | Water: <0.05 mg |