Quinidine-d3 is intended for use as an internal standard for the quantification of quinidine by GC- or LC-MS. Quinidine is a stereoisomer of the antimalarial agent quinine and a class Ia antiarrhythmic agent.1,2 Quinidine blocks the voltage-gated sodium (Nav) channel Nav1.5 in a use-dependent manner.1 It decreases the amplitude and duration of action potentials in isolated canine ventricular myocytes.3 Quinidine inhibits KKr, peak INa, and late INa (IC50s = 4.5, 11, and 12 μM, respectively) and can induce torsade de pointes in isolated rabbit hearts when used at a concentration of 1 μM.2 It induces QT prolongation in dogs.4 Quinidine also binds to M2 muscarinic acetylcholine receptors (Ki = 7.5 μM for human recombinant receptors expressed in HM2-B10 cells).5 Formulations containing quinidine have been used in the treatment of atrial fibrillation and ventricular arrhythmias.

|1. Roden, D.M. Pharmacology and toxicology of Nav1.5-class 1 anti-arrhythmic drugs. Card. Electrophysiol. Clin. 6(4), 695-704 (2014).|2. Wu, L., Guo, D., Li, H., et al. Role of late sodium current in modulating the proarrhythmic and antiarrhythmic effects of quinidine. Heart Rhythm 5(12), 1726-1734 (2008).|3. Salata, J.J., and Wasserstrom, J.A. Effects of quinidine on action potentials and ionic currents in isolated canine ventricular myocytes. Circ. Res. 62(2), 324-337 (1988).|4. Rakhit, A., Guentert, T.W., Holford, N.H.G., et al. Pharmacokinetics and pharmacodynamics of quinidine and its metabolite, quinidine-N-oxide, in beagle dogs. Eur. J. Drug Metab. Pharmacokinet. 9(4), 315-324 (1984).|5. Kovacs, I., Yamamura, H.I., Waite, S.L., et al. Pharmacological comparison of the cloned human and rat M2 muscarinic receptor genes expressed in the murine fibroblast (B82) cell line. J. Pharmacol. Exp. Ther. 284(2), 500-507 (1998).