QT prolongation and proarrhythmia by moxifloxacin: concordance of preclinical models in relation to clinical outcome

Abstract

Moxifloxacin, a fluoroquinolone antibiotic associated with QT prolongation, has been recommended as a positive control by regulatory authorities to evaluate the sensitivity of both clinical and preclinical studies to detect small but significant increases in QT interval measurements. In this study, we investigated effects of moxifloxacin on the hERG current in HEK-293 cells, electrocardiograms in conscious telemetered dogs, and repolarization parameters and arrhythmogenic potentials in the arterially perfused rabbit ventricular wedge model. Moxifloxacin inhibited the hERG current with an IC50 of 35.7 microM. In conscious telemetered dogs, moxifloxacin significantly prolonged QTc at 30 and 90 mg kg(-1), with mean serum Cmax of 8.52 and 22.3 microg ml(-1), respectively. In the wedge preparation, moxifloxacin produced a concentration-dependent prolongation of the action potential duration, QT interval, and the time between peak and end of the T wave, an indicator for transmural dispersion of repolarization. Phase 2 early after-depolarizations were observed in one of five experiments at 30 microM and five of five experiments at 100 microM. The arrhythmogenic potential was also concentration-dependent, and 100 microM ( approximately 18-fold above the typical unbound Cmax exposure in clinical usage) appeared to have a high risk of inducing torsade de pointes (TdP). Our data indicated a good correlation among the concentration-response relationships in the three preclinical models and with the available clinical data. The lack of TdP report by moxifloxacin in patients without other risk factors might be attributable to its well-behaved pharmacokinetic profile and other dose-limiting effects.

Figure 1

Effect of moxifloxacin on the hERG potassium current stably expressed in HEK-293 cells. (a) Current traces from a representative cell before and after applications of moxifloxacin at various concentrations administrated incrementally. The hERG current was elicited by a voltage protocol shown in the upper panel at 0.25 Hz. (b) Time course of the moxifloxacin effect on the hERG current. Peak tail current amplitudes were measured during the ramp repolarization phase and plotted against time. A steady-state current level was reached before application of next concentration of the drug. A linear fit was conducted in every experiment to the stable control period to account for the rundown of the current, if any. Amplitude of the current at the end of each concentration application was measured and compared with its corresponding control. (c) Concentration–response of the hERG blockade by moxifloxacin. Averaged data were obtained from four to seven experiments and fitted with a Hill equation. The resulting IC₅₀ was 35.7 μM with a Hill coefficient of 1.0.

Figure 2

Effect of moxifloxacin on HR, QT, and QTc in conscious telemetered dogs. Data were obtained from eight animals (four male and four female) of a Latin Square design. Each dog received a single dose of moxifloxacin by oral gavage at doses of 10, 30, and 90 mg kg⁻¹ and vehicle (0.5% methylcellulose/0.1% polysorbate 80) with a 7-day interdose washout period between each administration. Mean±s.e.m. ^*P<0.05 vs vehicle control.

Figure 3

Effects of moxifloxacin on action potentials recorded from epicardial and endocardial regions and transmural ECG in a rabbit wedge preparation. The numbers denote traces obtained in the absence (0) and presence of 3, 10, 30, and 100 μM moxifloxacin (1–4, respectively) from a representative experiment. An EAD was apparent in the epicardial action potential by 100 μM moxifloxacin.

Figure 4

Effects of moxifloxacin on repolarization parameters in the wedge preparation. Summary of the concentration-dependent effect of moxifloxacin on APDs, QT interval, and T_P–E at 0.5 Hz (a) and 1 Hz (b). Open and closed symbols in the APD panels represent endocardial and epicardial regions, respectively. For clarity purpose, the statistical significance of differences in stimulation frequency, recording sites, and concentrations are not noted.

Figure 5

Phase 2 early after-depolization (EAD) induced by 100 μM moxifloxacin. The tissue was stimulated at 0.5 Hz. EADs in action potentials with or without ‘R-on-T' in transmural ECGs were seen in all five at 100-μM and one of five at 30-μM experiments.

Figure 6

Correlation of preclinical assessment results with the clinical exposures. ^*Unbound C_max following oral treatment of 400 mg, QD for 10 days (Balfour & Wiseman, 1999). For conscious telemetered dogs, mean maximal QTc prolongation was plotted against unbound C_max at each dose. The arrhythmogenic (AG) scores in the wedge preparation were obtained by a sum of the individual parameter-associated scores (Table 2) in each experiment, and then averaged at each concentration.