ABSTRACT
Objectives: This study aimed to compare the QTc interval between low and high dose methadone groups and evaluate the pattern of QTc variation
Methods: This is a prospective cohort study conducted from December 2010 till August 2011 at Malaysian University of Science's Hospital. Forty six subjects, grouped in high dose [>80mg] and low dose [<80mg] oral methadone, were followed-up at 4-weekly for QTc measurements. Relevant demographic and biochemical profiles were taken at intervals with concurrent QTc measurements
Results: No significant QTc differences between methadone dosage groups were found at Week 0 [434ms vs 444ms, p = 0.166] and week 8 [446.5ms vs 459ms, p = 0.076], but not at week 4[435ms vs 450ms, p = 0.029]. However, there were significant associations between the groups with QTc prolongation at week 0 and 4 [OR 4.29[95% CI 1.01, 18.72] p=0.044 and OR 5.18 [95% CI 1.34, 20.06] p =0.013, respectively] but not at week 8 [OR 2.44 [95% CI 0.74, 8.01] p=0.139]. On multivariate analysis, dose group was the sole significant factor for QTc prolongation for week 0 and 4 [p values 0.047 and 0.017, respectively], but not at week 8
Conclusion: High-dose methadone group is more likely to develop prolonged QTc than low-dose group. However, such effects were inconsistent and occurred even during chronic methadone therapy, mandating judicious QTc and serum methadone monitoring