Concentration-QT Analysis in the Presence of Pharmacokinetic and/or Pharmacodynamic Interaction
*Garnett Christine, Pharmacometrics, FDA  *Jogarao Gobburu, Pharmacometrics, FDA  *Yaning Wang, Pharmacometrics, FDA  *Hao Zhu, Pharmacometrics, FDA 

Keywords: Concentration-QT analysis, Ketoconazole, Drug-Drug Interaction

The concentration-QT analysis was to tease out PK and potential PD interactions to assess if a test drug prolongs QT. This was a thorough QT study. Subjects received test drug and/or ketoconazole and placebo. A multivariate mixed-effects linear CQT model for both ketoconazole and test drug was used to describe the overall QT effect. The test drug and ketoconazole each caused maximum mean ddQTc of 1.7 ms and 5.5 ms. When coadministered, the maximum mean ddQTc was 9.9 ms, despite only an 18% increase in tested drug exposure. There was an additive effect on the QT interval when using ketoconazole with tested drug; with ketoconazole being the primary drug for prolonging the QT interval.Even at supratherapeutic concentrations test drug had minimal effects on the QT interval of 1.2 ms. The CQT analysis supported the regulatory decision that the test drug did not prolong QT in a meaningful way.