Paroxetine HCl Hemihydrate API is the hemihydrate form of Paroxetine Hydrochloride, a selective serotonin reuptake inhibitor (SSRI) pharmaceutical active ingredient. Paroxetine Hydrochloride exists in both anhydrous and hemihydrate forms, and the distinction is important for API identification, molecular weight, water content and pharmaceutical quality documentation. USP identifies the hemihydrate specifically by CAS Number 110429-35-1 and molecular weight 374.83 g/mol.
The chemical formula of Paroxetine Hydrochloride Hemihydrate is C19H20FNO3·HCl·½H2O, which can also be represented as C19H21ClFNO3·0.5H2O. Its molecular weight is 374.83 g/mol. The anhydrous form, in contrast, has CAS Number 78246-49-8 and molecular weight 365.83 g/mol. These two forms should not be mixed in an API database or CMS because their water content and solid-state characteristics are different.
FDA's Substance Registration System identifies 110429-35-1 specifically with Paroxetine Hydrochloride Hemihydrate and gives the hydrate composition corresponding to two Paroxetine Hydrochloride units with one molecule of water.
Paroxetine is an SSRI that increases serotonergic activity by inhibiting the serotonin transporter. Paroxetine-containing pharmaceutical products are used for approved indications that can include major depressive disorder, panic disorder, social anxiety disorder and other psychiatric conditions depending on the specific formulation and regulatory authorization.
As an API, Paroxetine Hydrochloride requires control of chemical purity, assay, stereochemical identity, residual solvents and hydrate state. The hemihydrate form is particularly important because the water of crystallization contributes to its defined molecular weight and must remain within the appropriate pharmacopoeial range.
For accurate product data, the two forms should be maintained separately:
Paroxetine HCl Hemihydrate
Paroxetine HCl Anhydrous
USP confirms that Paroxetine Hydrochloride can exist as either the anhydrous form or a form containing half a molecule of water of hydration. The same USP definition specifies assay on an anhydrous and solvent-free basis.
The USP monograph provides an assay range of 98.5–102.0%, calculated as Paroxetine Hydrochloride on the anhydrous and solvent-free basis. Water content is separately controlled at 2.2–2.8% for the hemihydrate form.
The monograph also specifies residue on ignition NMT 0.1% and heavy metals 0.002%, equivalent to 20 ppm.
The related-substances procedure controls Paroxetine Related Compound B, F and G, together with unspecified impurities. The current USP revision identifies limits of 0.5% for Related Compound B, 0.2% for Related Compound F, 0.2% for Related Compound G, 0.1% for any unspecified impurity and 1.0% for total impurities.
A qualified Paroxetine HCl Hemihydrate API Manufacturer in India should maintain controlled synthesis, purification, crystallization and drying processes to consistently obtain the required hemihydrate form.
Control of water content is particularly important because the hemihydrate contains approximately one-half molecule of water per molecule of Paroxetine Hydrochloride. The USP specification of 2.2–2.8% water provides a direct quality-control parameter for distinguishing the intended hemihydrate form.
Analytical quality control can include IR identification, chloride identification, HPLC assay, chromatographic impurity testing, water determination, residue on ignition and elemental/heavy-metal controls.
Commercial Paroxetine HCl Hemihydrate API documentation may include a Certificate of Analysis, specification sheet, analytical methods, impurity profile, residual-solvent information, water-content results and stability information.
For accurate CMS data, the primary product should be identified as Paroxetine Hydrochloride Hemihydrate, CAS 110429-35-1, rather than using the CAS number of the anhydrous form.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.5–102.0% |
| Loss on Drying | NMT 1.0% |
| Residue on Ignition | NMT 0.1% |
| Heavy Metals | NMT 20 ppm |
| Total Impurities | NMT 1.0% |
| Water Content | 2.2–2.8% |