Primidone is a synthetic anticonvulsant belonging to the deoxybarbiturate class. It is chemically identified as 5-ethyl-5-phenyl-1,3-diazinane-4,6-dione, with the molecular formula C₁₂H₁₄N₂O₂ and molecular weight 218.25 g/mol. Its CAS Number is 125-33-7. NIST confirms the chemical identity, molecular formula, molecular weight and CAS number.
Primidone is also known by synonyms including 2-Deoxyphenobarbital, Desoxyphenobarbital, Primaclone and 5-Ethyl-5-phenylhexahydropyrimidine-4,6-dione. It is an established pharmaceutical active ingredient used primarily for its anticonvulsant activity.
Product Name: Primidone
CAS Number: 125-33-7
Molecular Formula: C₁₂H₁₄N₂O₂
Molecular Weight: 218.25 g/mol
IUPAC Name: 5-Ethyl-5-phenyl-1,3-diazinane-4,6-dione
Synonyms: 2-Deoxyphenobarbital; Desoxyphenobarbital; Primaclone
API Class: Anticonvulsant / Deoxybarbiturate
Appearance: White or almost white crystalline powder
Melting Range: 279–284°C
The substance is chemically related to barbiturate compounds but differs from phenobarbital by the replacement of the 2-oxo functionality, which is reflected in its designation as a deoxybarbiturate. NIST and international monograph references support the above chemical identity.
Primidone is a synthetic anticonvulsant API with a pyrimidinedione ring system containing ethyl and phenyl substituents. Its molecular structure provides the physicochemical and pharmacological characteristics associated with this established antiepileptic compound.
Primidone is metabolized in the body to pharmacologically active metabolites, particularly phenobarbital and phenylethylmalonamide (PEMA). Its established pharmaceutical use is associated with seizure management and anticonvulsant therapy.
The API is generally described as a white or almost white crystalline powder. It is very slightly soluble in water and slightly soluble in ethanol, while alkaline solutions can improve its solubility.
Primidone API is primarily used in the manufacture of pharmaceutical products intended for anticonvulsant therapy. It is an established antiepileptic medicine and has also been used in the management of certain forms of tremor.
Its pharmaceutical application is based on its anticonvulsant activity and its metabolism to active compounds. Finished pharmaceutical products may be supplied in different strengths and dosage forms according to the approved formulation and applicable regulatory requirements.
For API manufacturing, the exact quality specification should be established according to the intended dosage form, applicable pharmacopoeial requirements and customer-specific regulatory requirements.
Primidone has a USP-NF monograph defining the API at NLT 98.0% and NMT 102.0%, calculated on the dried basis. The USP identification includes infrared absorption and ultraviolet absorption, while the monograph also includes a chemical identification reaction.
The USP monograph specifies loss on drying NMT 0.5%, determined after drying at 105°C for 2 hours, and residue on ignition NMT 0.2%. The USP melting range is 279–284°C.
The Japanese Pharmacopoeia similarly specifies loss on drying NMT 0.5% at 105°C for 2 hours and residue on ignition NMT 0.2%, providing additional compendial support for these numerical quality attributes.
For modern commercial API quality control, HPLC can be used for assay and related-substance evaluation where validated for the specific method. Commercial analytical material specifications also report HPLC purity of NLT 98.0 area%, although this should be distinguished from the USP assay procedure, which is spectrophotometric rather than an HPLC assay.
Primidone API manufacturing requires controlled chemical processing, purification, drying and analytical testing to achieve consistent pharmaceutical quality. A qualified Primidone API manufacturer in India can support pharmaceutical companies with controlled production and batch-specific quality documentation.
Manufacturing controls should cover raw-material qualification, reaction control, purification, drying, physical-property monitoring and final release testing. Particular attention should be given to assay, related impurities, moisture, residue on ignition and identification.
Batch documentation can be aligned with applicable pharmacopoeial and customer requirements. Analytical testing should use validated or appropriately qualified methods suitable for the intended API specification.
Primidone should be stored in suitable, well-closed or tight pharmaceutical containers to protect the material from contamination and environmental exposure.
The USP monograph specifies well-closed containers for preservation.
Commercial analytical references recommend storage in a cool, dark environment below 15°C. For commercial API, the final storage condition should be based on validated stability data and the approved packaging configuration.
Typical documentation for Primidone API may include:
All documents should identify the exact API as Primidone, CAS 125-33-7, to avoid confusion with phenobarbital and other structurally related compounds.
Primidone is an established anticonvulsant API supported by recognized pharmacopoeial specifications. USP defines an assay range of 98.0–102.0% on the dried basis, while compendial references specify loss on drying NMT 0.5%, residue on ignition NMT 0.2% and a melting range of 279–284°C.
A qualified Primidone API manufacturer in India can provide pharmaceutical-grade material supported by controlled manufacturing, analytical quality testing and comprehensive batch documentation.
| 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% |
| Melting Point | 279–284°C. |