Assessment of proarrhythmic activity of chloroquine in in vivo and ex vivo rabbit models

Objectives: To evaluate the prolongation of ventricular repolarization and proarrhythmic activity of antimalarial drug chloroquine in two rabbit proarrhythmia models viz., in vivo alpha 1 adrenoceptor-stimulated anesthetized rabbit and ex vivo isolated Langendorff rabbit heart using clofilium as standard proarrhythmic agent. Materials and Methods: In the in vivo model, three groups of rabbits, anesthetized by pentobarbitone sodium and a-chloralose, sensitized with a 1 agonist methoxamine followed by either continuous infusion of saline (control) or clofilium (3 mg/kg) or chloroquine (21 mg/kg) for 30 min. In ex vivo model, rabbit hearts were perfused with clofilium (10 mu M) or chloroquine (300 mu M) continuously after priming along with methoxamine, acetylcholine chloride and propranolol hydrochloride. Results: In these models, prolongation of repolarization during alpha 1 -adrenoceptor stimulation produced early after depolarization (EAD) and Torsade de pointes (TdP). Saline infusion did not induce any abnormality in the animals. Clofilium caused expected changes in the electrocardiogram in both the models including TdP (50.0% in in vivo and 66.67% in ex vivo). Chloroquine caused decrease in heart rate and increase in the corrected QT (QTc) interval in both the models. Further, apart from different stages of arrhythmia, TdP was evident in 33.33% in ex vivo model, whereas no TdP was observed in in vivo model. Conclusions: The results indicated that proarrhythmic potential of chloroquine and clofilium was well evaluated in both the models; moreover, both the models can be used to assess the proarrhythmic potential of the new drug candidates.