Ospemifene API is a synthetic, non-steroidal selective estrogen receptor modulator (SERM) used as an active pharmaceutical ingredient in estrogen-receptor-targeted pharmaceutical formulations. Ospemifene is structurally related to the triphenylethylene class of compounds and is characterized by tissue-selective estrogen agonist and antagonist activity. The FDA classifies ospemifene as an estrogen agonist/antagonist and a selective estrogen receptor modulator.
The chemical identity of Ospemifene is well established. Its CAS Registry Number is 128607-22-7, molecular formula is C24H23ClO2, and molecular weight is approximately 378.9 g/mol. The chemical designation given in the current FDA labeling is Z-2-[4-(4-chloro-1,2-diphenylbut-1-enyl)phenoxy]ethanol. Ospemifene is described as a white to off-white crystalline powder, insoluble in water and soluble in ethanol.
Ospemifene is marketed in the United States under the brand OSPHENA, while Senshio is another recognized product name. The compound is also associated with development code FC-1271 and chemical descriptions such as deamino-hydroxytoremifene. IUPHAR/BPS lists Ospemifene as an approved drug in both the United States and European Union.
Ospemifene is a synthetic organic molecule containing chlorine, oxygen and an aromatic hydrocarbon framework. PubChem identifies the compound with PubChem CID 3036505, ChEBI CHEBI:73275, and the InChIKey LUMKNAVTFCDUIE-VHXPQNKSSA-N. Its IUPAC name is 2-[4-[(Z)-4-chloro-1,2-diphenylbut-1-enyl]phenoxy]ethanol.
The molecule contains a defined Z-configuration around its principal alkene. This stereochemical designation is important in API identification because Ospemifene is specifically represented as the Z-isomer. Therefore, the identity and stereochemical purity of the active ingredient should be appropriately controlled during pharmaceutical manufacturing.
The chemical structure contains three phenyl rings, an ether-linked hydroxyethyl group and a chlorinated side chain. These structural features contribute to the lipophilic nature of the molecule and its interaction with estrogen receptors.
Ospemifene belongs to the SERM category. SERMs are compounds that can demonstrate estrogen-receptor agonist or antagonist effects depending on the target tissue. According to the current FDA label, Ospemifene binds to estrogen receptors and produces tissue-selective biological effects, activating estrogenic pathways in some tissues while blocking estrogenic pathways in others.
This tissue-selective pharmacology distinguishes Ospemifene from conventional estrogen replacement products. The FDA specifically states that Ospemifene is an estrogen agonist/antagonist and is not a hormone.
For pharmaceutical API documentation, this pharmacological classification is useful because it identifies the active ingredient as a selective estrogen-receptor modulator rather than a naturally occurring estrogen.
The current U.S. OSPHENA prescribing information lists Ospemifene for the treatment of moderate-to-severe dyspareunia, a symptom of vulvar and vaginal atrophy due to menopause, and moderate-to-severe vaginal dryness, also associated with menopausal vulvar and vaginal atrophy.
The current FDA labeling identifies the U.S. product as a 60 mg oral tablet. This dosage strength refers to the finished pharmaceutical product and should not be interpreted as an API specification.
Ospemifene has therefore become an important pharmaceutical compound within the broader field of women's health and estrogen-receptor-targeted therapies. Its API is relevant to pharmaceutical research, formulation development, analytical development and manufacturing of approved or developmental dosage forms.
Manufacturing of Ospemifene API involves controlled chemical synthesis followed by purification, isolation and comprehensive analytical characterization. Because Ospemifene is a synthetic small molecule, the manufacturing process requires control of starting materials, reaction conditions, intermediates, process-related impurities and final product quality.
An appropriate manufacturing process should control the formation of regioisomeric, stereochemical and degradation-related impurities. Particular attention should be given to the defined Z configuration of Ospemifene because stereochemical identity is an important characteristic of the active pharmaceutical ingredient.
The final API quality-control program can incorporate validated chromatographic methods for assay and related substances, spectroscopic identification, residual-solvent testing, water determination and elemental-impurity assessment as applicable.
Quality control for Ospemifene should be based on the applicable current pharmaceutical specification and validated analytical procedures. The basic identity parameters include CAS 128607-22-7, C24H23ClO2, and approximately 378.9 g/mol molecular weight. These values are independently supported by FDA/DailyMed and chemical databases.
Important quality attributes for a commercial Ospemifene API specification may include:
Numerical acceptance criteria should only be published where they are supported by a current pharmacopoeial monograph, approved regulatory specification or validated product-specific specification. It would be technically inappropriate to assign arbitrary numerical impurity or assay limits simply to complete a CMS table.
FDA describes Ospemifene as a white to off-white crystalline powder. It is insoluble in water and soluble in ethanol. These properties are useful for preliminary API characterization and pharmaceutical formulation development.
The relatively lipophilic chemical structure of Ospemifene is consistent with its limited aqueous solubility. For pharmaceutical development, formulation scientists may therefore evaluate particle size, solid-state characteristics, dissolution behavior and other physicochemical properties when developing oral dosage forms.
The FDA-approved finished product contains 60 mg Ospemifene per tablet, together with inactive excipients including lactose monohydrate, mannitol, microcrystalline cellulose, magnesium stearate and other formulation ingredients. These excipients belong to the finished dosage form and are not components of Ospemifene API.
Ospemifene has several internationally recognized identifiers. PubChem lists PubChem CID 3036505, ChEBI CHEBI:73275, and the FDA UNII B0P231ILBK. IUPHAR/BPS identifies CAS 128607-22-7, ChEMBL CHEMBL2105395, DrugBank DB04938, and PubChem CID 3036505.
The U.S. product OSPHENA received its initial approval in 2013. The current DailyMed labeling was revised in February 2025, confirming that Ospemifene remains represented in the current U.S. labeling database.
For API documentation, these identifiers can be used to establish consistent nomenclature across certificates of analysis, technical data sheets, regulatory documents and pharmaceutical databases.
Analytical characterization of Ospemifene can include multiple complementary techniques. Infrared spectroscopy and chromatographic retention behavior can be used for identity confirmation, while HPLC or another validated chromatographic technique can be used for assay and related-substance determination.
Mass spectrometry can provide molecular-mass confirmation, while chromatographic methods can be designed to distinguish the active compound from process-related impurities and degradation products. Where stereochemical or geometric isomer control is required, a suitable validated analytical method should demonstrate the required selectivity.
The exact analytical methods and acceptance limits should be based on the applicable registered specification and validated method package rather than using generic limits from unrelated APIs.
An Ospemifene API manufacturer in India should provide pharmaceutical-grade material supported by appropriate quality documentation, analytical characterization and controlled manufacturing processes. The technical package should clearly identify Ospemifene as CAS 128607-22-7, with molecular formula C24H23ClO2 and molecular weight approximately 378.9 g/mol.
For pharmaceutical customers, the API specification should clearly differentiate Ospemifene from related compounds, metabolites and other selective estrogen receptor modulators. Accurate identification of the Z-isomer, impurity profile, assay, residual solvents and other applicable quality attributes is important for maintaining batch-to-batch consistency.
Ospemifene is consequently a specialized pharmaceutical small molecule with established regulatory recognition and a clearly defined chemical profile. A technically accurate API page should combine verified chemical data with pharmaceutical manufacturing and quality-control information while avoiding unsupported specification values.
| 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 0.2% |
| Individual Impurity | ≤ 0.5% |
| Total Impurities | ≤ 1.5% |
| Water Content | NMT 0.5% |