Abstract
Thermogravimetry (TG) and differential scanning calorimetry (DSC) are useful techniques that have been successfully applied in the pharmaceutical industry to reveal important information regarding the physicochemical properties of drug and excipient molecules such as polymorphism, stability, purity, formulation compatibility among others. Verapamil hydrochloride shows thermal stability up to 180 °C and melts at 146 °C, followed by total degradation. The drug is compatible with all the excipients evaluated. The drug showed degradation when subjected to oxidizing conditions, suggesting that the degradation product is 3,4-dimethoxybenzoic acid derived from alkyl side chain oxidation. Verapamil hydrochloride does not present the phenomenon of polymorphism under the conditions evaluated. Assessing the drug degradation kinetics, the drug had a shelf life (t90) of 56.7 years and a pharmaceutical formulation showed t90 of 6.8 years showing their high stability.
Highlights
Thermal analysis techniques allow the prior choice of more stable pharmaceutical formulations at a very short time, by means of evaluation of interactions that may exist, first, in their binary mixtures, and later in multicomponent mixtures
The differential scanning calorimetry (DSC) curves applied to compatibility studies may show changes in the fusion range, shape or area of the peaks and appearance and disappearance of thermal events after mixing two components, indicating interactions or chemical reactions, which must be confirmed by other analytical techniques
Verapamil hydrochloride showed degradation when subjected to oxidizing conditions, suggesting that the degradation product is the 3,4-dimethoxybenzoic acid, derived from the alkyl side chain oxidation
Summary
Verapamil hydrochloride (VRP, C27H38N2O4·HCl, I), a phenylalkylamine calcium-channel blocker, has broadly been used as an anti-arrhythmic drug to manage supraventricular tachyarrhythmias. After oral administration of VRP to humans, the drug is rapidly absorbed and widely distributed. It undergoes an extensive hepatic and intestinal first-pass metabolism, resulting in a low extent of absolute oral bioavailability in humans [13,14]. Verapamil hydrochloride has been described as an inhibitor of P-glycoprotein able to improve the chemotherapy response by reducing the resistance of cancer cells against antineoplasic agents [15]
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