© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Relationships between preclinical cardiac electrophysiology, clinical QT interval prolongation and torsade de pointes for a broad range of drugs: evidence for a provisional safety margin in drug development
aSafety Assessment UK, AstraZeneca R&D Alderley Park, Macclesfield, Cheshire SK10 4TG, UK
bCardiovascular Pharmacology, AstraZeneca R&D Mölndal, 431 83 Mölndal, Sweden
cAnimal Welfare Group, AstraZeneca R&D Alderley Park, Macclesfield, Cheshire SK10 4TG, UK
dDrug Safety, AstraZeneca R&D Charnwood, Loughborough, Leicestershire LE11 5RH, UK
eCovance Laboratories Limited, Otley Road, Harrogate, North Yorks HG3 1PY, UK
fMerck Research Laboratories, P.O. Box 4, West Point, PA 19486-00047, USA
gGlaxoSmithKline Safety Assessment, The Frythe, Welwyn, Herts AL6 9AR, UK
hPfizer Global Research and Development, Sandwich Laboratories, Ramsgate Road, Sandwich, Kent CT13 9NJ, UK
iDepartment of Cardiological Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK
* Corresponding author. Tel.: +44-1625-514-810; fax: +44-1625-513-779.
Objective: To attempt to determine the relative value of preclinical cardiac electrophysiology data (in vitro and in vivo) for predicting risk of torsade de pointes (TdP) in clinical use. Methods: Published data on hERG (or IKr) activity, cardiac action potential duration (at 90% repolarisation; APD90), and QT prolongation in dogs were compared against QT effects and reports of TdP in humans for 100 drugs. These data were set against the free plasma concentrations attained during clinical use (effective therapeutic plasma concentrations; ETPCunbound). The drugs were divided into five categories: (1) Class Ia and III antiarrhythmics; (2) Withdrawn from market due to TdP; (3) Measurable incidence/numerous reports of TdP in humans; (4) Isolated reports of TdP in humans; (5) No reports of TdP in humans. Results: Data from hERG (or IKr) assays in addition to ETPCunbound data were available for 52 drugs. For Category 1 drugs, data for hERG/IKr IC50, APD90, QTc in animals and QTc in humans were generally close to or superimposed on the ETPCunbound values. This relationship was uncoupled in the other categories, with more complex relationships between the data. In Category 1 (except amiodarone), the ratios between hERG/IKr IC50 and ETPCunbound (max) ranged from 0.1- to 31-fold. Similar ranges were obtained for drugs in Category 2 (0.31- to 13-fold) and Category 3 (0.03- to 35-fold). A large spread was found for Category 4 drugs (0.13- to 35 700-fold); this category embraced an assortment of mechanisms ranging from drugs which may well be affecting IKr currents in clinical use (e.g. sparfloxacin) to others such as nifedipine (35 700-fold) where channel block is not involved. Finally, for the majority of Category 5 drugs there was a >30-fold separation between hERG/IKr activity and ETPCunbound values, with the notable exception of verapamil (1.7-fold), which is free from QT prolongation in man; this is probably explained by its multiple interactions with cardiac ion channels. Conclusions: The dataset confirms the widely-held belief that most drugs associated with TdP in humans are also associated with hERG K+ channel block at concentrations close to or superimposed upon the free plasma concentrations found in clinical use. A 30-fold margin between Cmax and hERG IC50 may suffice for drugs currently undergoing clinical evaluation, but for future drug discovery programmes, pharmaceutical companies should consider increasing this margin, particularly for drugs aimed at non-debilitating diseases. However, interactions with multiple cardiac ion channels can either mitigate or exacerbate the prolongation of APD and QT that would ensue from block of IKr currents alone, and delay of repolarisation per se is not necessarily torsadogenic. Clearly, an integrated assessment of in vitro and in vivo data is required in order to predict the torsadogenic risk of a new candidate drug in humans.
KEYWORDS Antiarrhythmic agents; Arrhythmia (mechanisms); Ion channels; K-channel; Long QT syndrome; Repolarization; Sudden death; Ventricular arrhythmias
* The full, electronic version of this article is available on http://www.elsevier.com/homepage/sab/cardio/doc/Redfern_full.pdf
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