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Aim To study the differences in QTc interval on ECG in response to a single oral dose of rac-sotalol in men and women. Methods Continuous 12-lead ECGs were recorded in 28 men and 11 women on a separate baseline day and following a single oral dose of 160 mg rac-sotalol on the following day. ECGs were extracted at prespecified time points and upsampled to 1000 Hz and analyzed manually in a central ECG laboratory on the superimposed median beat. Concentration- QTc analyses were performed using a linear mixed effects model. Results Rac-sotalol produced a significant reduction in heart rate in men and in women. An individual correction method ( QTcI) most effectively removed the heart rate dependency of the QTc interval. Mean QTcI was 10 to 15 ms longer in women at all time points on the baseline day. Rac-sotalol significantly prolonged QTcI in both genders. The largest mean change in QTcI (Δ QTcI) was greater in females (68 ms (95% confidence interval ( CI) 59, 76 ms) vs. 27 ms (95% CI 22, 32 ms) in males). Peak rac-sotalol plasma concentration was higher in women than in men (mean Cmax 1.8 μg ml−1 (range 1.1-2.8) vs. 1.4 μg ml−1 (range 0.9-1.9), P = 0.0009). The slope of the concentration-Δ QTcI relationship was steeper in women (30 ms per μg ml−1 vs. 23 ms per μg ml−1 in men; P = 0.0135). Conclusions The study provides evidence for a greater intrinsic sensitivity to rac-sotalol in women than in men for drug-induced delay in cardiac repolarization. [ABSTRACT FROM AUTHOR]