Salmeterol Xinafoate is a long-acting beta-2 adrenergic receptor agonist used as an active pharmaceutical ingredient in respiratory medicines. It is the xinafoate salt of salmeterol and is widely associated with long-acting bronchodilator formulations used in the management of respiratory conditions such as asthma and chronic obstructive pulmonary disease. Salmeterol Xinafoate is identified by CAS Number 94749-08-3 and has a molecular formula of C36H45NO7 with a molecular weight of approximately 603.75 g/mol. FDA substance records identify Salmeterol Xinafoate as a bronchodilator and PubChem describes it as a selective beta-2 adrenergic receptor agonist.
Salmeterol Xinafoate provides the salmeterol active moiety in a stable pharmaceutical salt form. Salmeterol is structurally characterized by a saligenin ethanolamine portion and a lipophilic side chain that contributes to its prolonged interaction with beta-2 adrenergic receptors. Activation of beta-2 receptors increases intracellular cyclic AMP in airway smooth muscle, resulting in relaxation of bronchial smooth muscle and prolonged bronchodilation.
The xinafoate salt is therefore an important pharmaceutical form for development and manufacture of inhalation products containing salmeterol. The substance is commonly used in dry-powder inhalation and other inhalation-based pharmaceutical formulations.
Salmeterol Xinafoate is represented as C25H37NO4·C11H8O3, corresponding to the complete molecular formula C36H45NO7. Its molecular weight is approximately 603.75 g/mol. The salt contains the salmeterol component and 1-hydroxy-2-naphthoic acid, commonly referred to as xinafoic acid. PubChem identifies the parent Salmeterol under CAS 89365-50-4 and Salmeterol Xinafoate under CAS 94749-08-3.
The material is generally described as a white or almost-white crystalline powder or solid. Reference data report that it is practically insoluble or insoluble in water, soluble in methanol and slightly soluble in ethanol. A reference melting/decomposition temperature of approximately 138°C has also been reported.
Salmeterol Xinafoate is primarily used in respiratory pharmaceutical manufacturing. As a long-acting beta-2 agonist, salmeterol provides prolonged bronchodilation and is incorporated into inhalation medicines for long-term control of airflow limitation.
The API is particularly relevant to dry-powder inhalation products and combination respiratory formulations. It may also be combined with inhaled corticosteroids such as fluticasone propionate in fixed-dose respiratory products. For pharmaceutical manufacturers, control of particle characteristics, chemical purity and solid-state properties can be important because inhaled APIs must meet stringent requirements for formulation performance.
Salmeterol Xinafoate has established pharmacopoeial analytical requirements. The current USP 2025 specification defines the substance at 98.0–102.0% on a water- and solvent-free basis. Identification includes infrared spectroscopy and chromatographic retention-time comparison. The USP assay uses liquid chromatography with UV detection at 278 nm.
Current USP organic-impurity testing controls several specified Salmeterol-related impurities, including Salmeterol Related Compound A, Salmeterol-phenylethoxy, Salmeterol-phenylpropoxy, Salmeterol-O-alkyl, Salmeterol Related Compound B, Salmeterol-deoxy and Salmeterol-N-alkyl. Individual limits range from 0.1% to 0.3%, while unspecified individual impurities are limited to 0.10% and total impurities to 0.9%.
USP also specifies water NMT 0.25% and residue on ignition NMT 0.1%. These values provide a strong basis for pharmaceutical API quality control.
Manufacturing Salmeterol Xinafoate for pharmaceutical applications requires control of chemical purity, related substances, moisture, inorganic residues and physical properties. Since the API is used in inhalation formulations, appropriate control of particle characteristics and solid-state properties can also be important during downstream product development.
Analytical testing can include FTIR identification, HPLC assay and related-substance testing, water determination, residue on ignition and other applicable quality tests. Solutions containing salmeterol should be protected from light during analytical procedures, as noted in the USP method.
Salmeterol Xinafoate should be protected from moisture, contamination and excessive environmental exposure. Current USP information specifies preservation in tight containers and storage at a temperature not exceeding 30°C.
Reference suppliers additionally recommend cool and dark storage for analytical material. Commercial API storage should ultimately follow the validated stability data and approved product specification.
Typical pharmaceutical API documentation may include a Certificate of Analysis, product specification, batch analytical report, HPLC chromatograms, impurity profile, water-content result, residual-solvent information, Safety Data Sheet and applicable technical or regulatory documentation.
Salmeterol Xinafoate is a well-established respiratory API with recognized USP and European pharmacopoeial analytical requirements. Its defined assay range, impurity profile, water specification and inorganic-residue control provide a strong quality framework for pharmaceutical manufacturing.
Consistent manufacturing, validated analytical testing and appropriate control of the API's chemical and physical characteristics are essential for reliable production of salmeterol-containing inhalation medicines.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Residue on Ignition | NMT 0.10% |
| Total Impurities | NMT 0.90% |
| Water Content | NMT 0.25% |