Demonstrating the statistical and pharmacological sensitivity of nonclinical QTc analysis using a dofetilide...

Nonclinical QTc studies can augment clinical QTc assessments in regulatory submissions provided they are of sufficient quality and sensitivity. Both the statistical performance and species translation play a role in determining the sensitivity of the model. The current analyses examine the effects of dofetilide or vehicle on the QT interval in nonhuman primate (NHP; n = 16) using a one-step estimated marginal means method where both treatment and animal ID are used in regression models to avoid a separate rate correction step, in comparison to other commonly utilized methods. The doses of dofetilide were chosen to span a threshold dose with exposure only just exceeding the concentration associated with 10 ms QTc prolongation in man, to a dose where exposures exceed the Emax for QTc prolongation. The primary objective was an evaluation of which doses and exposures can be detected as eliciting a statistically significant change in QTc. A group size of 8 for cross-over analysis was insufficient to detect, as statistically significant, the effects of the threshold dose of 0.01 mg/kg dofetilide using common correction and statistical analysis methods and hourly time intervals. Higher doses were all detected as causing a statistically significant effect using the same techniques. The 'One-Step' method was able to detect as statistically significant effects at all doses of dofetilide across a wide range of time and exposure. There were also temporal differences between the mean effects observed using the common and 'One-Step' methods. Preliminary concentration-QTc assessment suggests a higher maximum prolongation in concentration QTc with the 'One-Step' method. Furthermore, this analysis suggests that at exposures associated with a 10 ms QTc prolongation in man a 10 ms prolongation is also observed in NHP. The observed ED₅₀ concentration (0.85 ng/ml unbound) is close to that described in man (0.98 ng/ml). These analyses demonstrate the statistical sensitivity of the 'One-Step' method of QTc assessment in NHP. The pharmacological sensitivity was also demonstrated and a detection threshold of 10 ms was consistent in terms of exposure between NHP and man. Overall, QTc assessment using the 'One-Step' method in NHP is a robust and sensitive model to supplement clinical QTc assessment.