Quinidine is a naturally derived cinchona alkaloid and an established pharmaceutical active ingredient belonging to the class of antiarrhythmic agents. It is the dextrorotatory stereoisomer related to quinine and has historically been used for its electrophysiological effects on cardiac tissue. The exact free-base API has the molecular formula C₂₀H₂₄N₂O₂, molecular weight 324.42 g/mol, and CAS Number 56-54-2. NIST reports a molecular weight of 324.4168 g/mol, while PubChem identifies CAS 56-54-2 for quinidine.
Quinidine occurs as crystals or a white powder. The Brazilian Pharmacopoeia describes it as white or nearly white crystals and reports an approximate melting temperature of 172°C. It is very slightly soluble in water, moderately soluble in ethyl alcohol and slightly soluble in methyl alcohol.
Product Name: Quinidine
Synonyms: (+)-Quinidine, Conquinine, Conchinine, Pitayine, Quinidine Base
CAS Number: 56-54-2
Molecular Formula: C₂₀H₂₄N₂O₂
Molecular Weight: 324.42 g/mol
Chemical Class: Cinchona Alkaloid
Pharmaceutical Class: Class Ia antiarrhythmic
API Form: Free base
Appearance: White or nearly white crystals / crystalline powder
Melting Point: Approximately 172°C
Specific Rotation: Approximately +260° at 20°C
Storage: Protected from light
PubChem identifies quinidine as a cinchona alkaloid and records its roles including antiarrhythmic drug, sodium-channel blocker, potassium-channel blocker and muscarinic antagonist.
Quinidine is structurally related to quinine but differs in stereochemistry. It is a chiral cinchona alkaloid and therefore optical rotation is an important identity and characterization parameter. The Brazilian Pharmacopoeia specifies a specific rotation of approximately +260°, determined at 20°C using a 1% w/v solution in ethyl alcohol.
Commercial analytical references also report positive optical rotation in the range of approximately +250° to +275° depending on the test conditions and specification. A recent Thermo Fisher specification, for example, reports +250° to +270° (c=1 in ethanol) and a melting point of 165–175°C. This is a commercial product specification and should not be confused with a universal pharmacopoeial release limit.
Quinidine's pharmaceutical activity is associated with blockade of cardiac sodium channels and effects on cardiac electrophysiology. It has historically been used as a Class Ia antiarrhythmic agent. Quinidine also exhibits potassium-channel blocking and other pharmacological effects.
Quinidine has an established pharmaceutical history as an antiarrhythmic drug. It acts primarily by modifying cardiac electrical conduction and prolonging the action potential and refractory period.
Historically, quinidine and its pharmaceutical salts have been used in the management of certain supraventricular and ventricular cardiac arrhythmias. The clinical use of quinidine depends on the specific approved product, indication and regulatory market.
It is important to distinguish Quinidine free base from pharmaceutical salts such as Quinidine Sulfate and Quinidine Gluconate. These salts have different molecular formulas, molecular weights and pharmacopoeial specifications. PubChem specifically lists related CAS numbers for the sulfate salt separately from free-base quinidine.
Quinidine quality assessment requires control of chemical identity, stereochemical identity, assay, optical rotation, related alkaloids and physical characteristics.
The free-base material is commonly characterized by infrared spectroscopy and optical rotation. A recent analytical specification reports FTIR identification, non-aqueous acid-base titration assay, optical rotation and melting point as quality parameters.
Because quinidine is a natural-product-derived alkaloid, related alkaloids and degradation products can be important quality attributes. Pharmaceutical-grade material should therefore be evaluated against the applicable pharmacopoeial or approved customer specification rather than relying only on a generic purity value.
The Brazilian Pharmacopoeia provides physical and chemical identification information including specific rotation, melting temperature, molecular formula and solubility.
Quinidine API manufacturing and processing require controlled raw-material selection, appropriate purification and comprehensive analytical testing. Because quinidine is a stereochemically defined alkaloid, identity and optical rotation are important characteristics for confirming the desired substance.
Manufacturing quality controls may include raw-material qualification, process monitoring, crystallization or purification controls, drying, optical-rotation testing, chromatographic purity analysis and final assay determination.
Batch specifications can be aligned with the intended pharmaceutical market and applicable pharmacopoeial or customer requirements.
Quinidine should be stored in suitable closed containers and protected from excessive light. The Brazilian Pharmacopoeia recommends protection from light, while commercial analytical information recommends controlled storage appropriate for the material.
Light protection is particularly relevant for quinidine and its salts because exposure to light can contribute to discoloration and chemical changes. Suitable packaging helps maintain API quality during storage and transportation.
Typical documentation for Quinidine API may include:
Quinidine is a well-characterized cinchona alkaloid with an established pharmaceutical history and defined chemical identity. Its CAS Number 56-54-2, molecular formula C₂₀H₂₄N₂O₂, molecular weight 324.42 g/mol, positive optical rotation and characteristic melting behavior provide important quality attributes for API identification.
Controlled manufacturing, stereochemical verification, chromatographic purity assessment and appropriate storage practices support consistent Quinidine API quality for pharmaceutical applications.
| 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 0.1% |
| Melting Point | 165–175°C |