QT prolongation in anaesthetized guinea‐pigs: an experimental approach for preliminary screening of torsadogenicity of drugs and drug candidates

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Abstract
Many non‐cardiovascular drugs can prolong the QT interval of the electrocardiogram (ECG); this is an accessory property not necessary for their pharmacological action and generally linked to the block of the potassium HERG channels and delayed cardiac repolarization. The QT prolongation can lead to a dangerous tachyarrhythmia, called torsade de pointes, and potentially to fatal ventricular fibrillation. The experimental approaches, aimed at an early identification of this undesidered property, often require sophisticated and expensive equipment or the use of superior animal species (dog, primates) that cannot be employed easily for ethical and/or economic reasons. This work aimed to study drug‐induced QT prolongation in anaesthetized guinea‐pigs and to evaluate the reliability of such an experimental approach to obtain a satisfying predictive parameter of the torsadogenicity of drugs in humans. Seven drugs that were torsadogenic in humans (astemizole, cisapride, haloperidol, quinidine, sotalol, terfenadine and thioridazine) and two that were non‐torsadogenic (chlorprotixene and diazepam) were administered i.v. to guinea‐pigs under pentobarbital anaesthesia. The ECGs were recorded by four electrodes inserted in the subcutaneous layer of the limbs. Both RR and QT intervals were measured in Leads II and III and then the correct QT values were calculated by Bazett and Fridericia algorithms (QTcB and QTcF, respectively). All the drugs, with the exception of chlorprotixene and diazepam, produced a dose‐dependent prolongation of the QT and RR intervals and a significant increase of QTcB and QTcF values. It can be concluded that this method represents a rapid and low‐cost procedure to evaluate the cardiac safety profile in the preliminary screening of a high number of drugs or drug candidates. Copyright © 2004 John Wiley & Sons, Ltd.