Orphenadrine API is a synthetic pharmaceutical active ingredient belonging to the class of centrally acting muscle relaxants. It is chemically related to diphenhydramine and possesses anticholinergic and antihistaminic properties. Orphenadrine is used in pharmaceutical preparations primarily for its muscle-relaxant and analgesic-associated properties, particularly in conditions involving painful skeletal-muscle spasm. PubChem describes Orphenadrine as a tertiary amino compound and identifies pharmacological activities including H1-receptor antagonism, muscarinic antagonism, NMDA-receptor antagonism, antiparkinson activity and centrally mediated muscle relaxation.
The Orphenadrine free base has the molecular formula C18H23NO and a molecular weight of 269.3813 g/mol, according to NIST. PubChem reports a rounded molecular weight of 269.4 g/mol. The CAS Registry Number for the free base is 83-98-7.
Orphenadrine is also known by several chemical and historical names, including Orphenadrin, Orphenadine, o-Methyldiphenhydramine, Norflex, Disipal and WS 2434. Its IUPAC name is N,N-dimethyl-2-[(2-methylphenyl)-phenylmethoxy]ethanamine.
From a pharmaceutical API perspective, Orphenadrine is a small-molecule tertiary amine containing an ether linkage, aromatic rings and a dimethylaminoethyl group. PubChem reports an exact mass of 269.177964357 Da, XLogP3 of 3.8, hydrogen-bond acceptor count of 2, rotatable bond count of 6, and topological polar surface area of 12.5 Ų.
These physicochemical characteristics are useful when developing analytical methods, evaluating formulation behavior and establishing appropriate API characterization procedures. Because Orphenadrine contains a basic tertiary amine, the pharmaceutical ingredient is also available in salt forms, most notably Orphenadrine Hydrochloride and Orphenadrine Citrate.
Orphenadrine Citrate is particularly important from a pharmaceutical and pharmacopoeial perspective. USP identifies Orphenadrine Citrate as C18H23NO·C6H8O7, with a molecular weight of 461.50 g/mol, CAS 4682-36-4, and a 1:1 relationship between Orphenadrine and citric acid. The current USP preview states that Orphenadrine Citrate contains NLT 98.0% and NMT 101.5%, calculated on the dried basis.
PubChem independently reports the Orphenadrine Citrate molecular formula as C24H31NO8 and molecular weight as 461.5 g/mol. It describes the material as the citrate salt of Orphenadrine.
This distinction is essential for an Orphenadrine API manufacturer in India, because the molecular weight and CAS number of the free base must not be substituted for the corresponding values of Orphenadrine Citrate.
Orphenadrine Hydrochloride is another salt form of the active moiety. PubChem lists the hydrochloride under CAS 341-69-5, with molecular formula C18H24ClNO and molecular weight 305.8 g/mol. It is described as an odorless white or almost white crystalline powder, with an aqueous-solution pH reported at approximately 5.5 in the cited reference data.
The hydrochloride therefore differs substantially from both the free base and citrate form:
These forms should be maintained as separate CMS/API records wherever the website offers individual products.
Orphenadrine is primarily recognized as a centrally acting muscle relaxant. Its pharmacological activity is not attributed to direct relaxation of skeletal muscle fibers alone; rather, its effects are associated with central nervous system mechanisms and anticholinergic properties. DailyMed describes Orphenadrine Citrate as the citrate salt of Orphenadrine and notes that its mode of therapeutic action has not been completely identified.
The compound has also been used in pharmaceutical contexts involving painful musculoskeletal conditions and muscle spasm. PubChem identifies Orphenadrine as a muscle relaxant and describes its physiological effect as centrally mediated muscle relaxation.
For pharmaceutical API documentation, these applications should be presented as pharmacological background rather than as direct treatment recommendations.
Manufacturing of Orphenadrine API involves controlled chemical synthesis followed by purification and analytical quality control. As a small-molecule pharmaceutical ingredient, manufacturing controls generally focus on starting-material quality, reaction control, process-related impurities, purification efficiency, residual solvents, assay and degradation products.
An effective manufacturing and quality system should establish appropriate controls throughout the production process. Analytical characterization can include chromatographic assay, related-substance testing, spectroscopic identification, water determination, residual-solvent analysis and elemental-impurity assessment where applicable.
For the Orphenadrine Citrate form, the USP monograph provides an authoritative benchmark for assay and identification. USP specifies identification using infrared spectroscopy and chromatographic retention-time comparison, and its monograph includes reference standards for Orphenadrine Citrate and several related compounds.
Quality control is an important component of pharmaceutical-grade Orphenadrine manufacturing. Identity testing confirms that the material corresponds to the intended active ingredient, while assay testing determines the quantity of the desired substance. Related-substance testing is used to control process impurities and degradation products.
For Orphenadrine Citrate, the verified USP definition requires 98.0–101.5% content on a dried basis. This is a useful numerical specification for the citrate salt because it comes directly from the USP monograph.
However, the same numerical value should not be transferred to Orphenadrine free base or Orphenadrine Hydrochloride. Different chemical forms require their own applicable specifications.
Parameters such as melting point, pH, water, residual solvents, sulfated ash and individual impurity limits should be stated only when supported by the applicable pharmacopoeial monograph or validated product specification. This avoids presenting reference data as mandatory universal API release criteria.
The free base can be identified using its established chemical structure and spectroscopic characteristics. NIST provides the standard molecular formula, molecular weight, InChI and InChIKey for Orphenadrine. PubChem further provides the canonical chemical structure, IUPAC name and calculated physicochemical properties.
For pharmaceutical-quality Orphenadrine, an analytical package may include:
The exact acceptance criteria should be derived from the applicable current specification rather than from generic small-molecule assumptions.
An Orphenadrine API manufacturer in India can support pharmaceutical development and manufacturing requirements through controlled production, analytical characterization and documented quality systems. Orphenadrine is a well-characterized small molecule with established chemical identifiers, while its citrate and hydrochloride salts provide alternative pharmaceutical forms.
For procurement and technical evaluation, it is particularly important to specify the exact form of the API. Orphenadrine free base (83-98-7) should not be confused with Orphenadrine Hydrochloride (341-69-5) or Orphenadrine Citrate (4682-36-4). Their molecular formulas, molecular weights and specifications are different.
A technically accurate Orphenadrine API specification should therefore combine verified chemical identity with appropriate quality-control requirements. For the citrate salt, the USP assay range provides a particularly useful authoritative numerical reference, while product-specific specifications should be used for other quality attributes when no universal numerical value is established.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0–101.5% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 0.5% |