Sample Size Re-Estimation without Breaking the Blind in Clinical Trial

From a regulatory perspective, it is important that the sample size recalculation is performed such that all persons involved in the study remain blinded. The proposed method is an extension of the work by Shih and Zhao (1997) to continuous endpoints. The treatment means are constructed by the convex combinations of the stratum means and then estimated by using the linear model of the stratum responses. In this article, the properties of the proposed estimators are studied. Simulation experiments are conducted to evaluate the difference between two estimators. The unblind estimators for the population mean and the population variance perform better than those of the blind estimators in terms of bias and mean square errors in the most of cases. Given a particular sample size, the accuracies of the blind means and the blind variances depend on the treatment proportions in each stratum. An example of interim analysis is given in this article to illustrate the use of sample size determination. The proposed sample size calculations are recommended in the interim analyses to meet Committee for Proprietary Medical Products requirement, retaining the blinding.

A new biomarker--index of cardiac electrophysiological balance (iCEB)--plays an important role in drug-induced cardiac arrhythmias: beyond QT-prolongation and Torsades de Pointes (TdPs)

INTRODUCTION

In the present study, we investigated whether a new biomarker - index of cardiac electrophysiological balance (iCEB=QT/QRS) - could predict drug-induced cardiac arrhythmias (CAs), including ventricular tachycardia/ventricular fibrillation (VT/VF) and Torsades de Pointes (TdPs).

METHODS

The rabbit left ventricular arterially-perfused-wedge was used to investigate whether the simple iCEB measured from the ECG is reflective of the more difficult measurement of λ (effective refractory period×conduction velocity) for predicting CAs induced by a number of drugs.

RESULTS

Dofetilide concentration-dependently increased iCEB and λ, predicting potential risk of drug-induced incidence of early afterdepolarizations (EADs) starting at 0.01μM. Digoxin (1 and 5μM), encainide (5 and 20μM) and propoxyphene (10 and 100μM) markedly reduced both iCEB and λ, predicting their ability to induce non-TdP-like VT/VF. At 10μM, both NS1643 and levcromakalim significantly decreased λ and iCEB, which was preceded with presence of non-TdP-like VT/VF. Isoprenaline (0.05 to 0.5μM) significantly reduced both λ and iCEB, which was associated with a high incidence of non-TdP-like VT/VF in most preparations. Other biomarkers (i.e. transmural dispersion of T-wave and instability of the QT interval) predicted only dofetilide-induced long QT and EADs, but did not predict drug-induced risk of non-TdP-like VT/VF.

DISCUSSION

Our data from 7 reference drugs of known pro-arrhythmic effects suggests that 1) this non-invasive iCEB predicts potential risk of drug-induced CAs beyond long QT and TdP; 2) iCEB is more useful than the current biomarkers (i.e. transmural dispersion and instability) in predicting potential risks for drug-induced non-TdP-like VT/VF.