Pharmacokinetic and pharmacodynamic modeling of the effects of oral and intravenous administrations of dofetilide on ventricular repolarization.

OBJECTIVES

To examine the pharmacokinetics and the relation between plasma concentrations of the new potassium channel blocker dofetilide and QTc prolongation on the surface electrocardiogram after oral and intravenous administration.

METHODS

Ten healthy volunteers received a single dose of 0.5 mg dofetilide orally and intravenously (over 30 minutes) in a randomized crossover study. The QTc interval versus dofetilide plasma concentration was analyzed by use of pharmacokinetic and pharmacodynamic modeling techniques.

RESULTS

Dofetilide absolute bioavailability and systemic clearance were 92% +/- 9% and 0.35 +/- 0.05 L/hr/kg, respectively. Mean maximum increase in QTc interval duration was 99 msec (27%) and 61 msec (16%) after intravenous and oral administration, respectively. A counterclockwise hysteresis loop between dofetilide plasma concentrations and QTc interval duration was observed after intravenous infusions in all subjects, whereas direct linear relationships were observed after oral administrations in eight of 10 subjects. Pharmacokinetic-pharmacodynamic modeling showed the consistency of the effect versus concentration relationships obtained with the two routes of administration. With use of a maximum effect (Emax) model and data obtained after intravenous infusion, mean maximum QTc prolongation (Emax) was 121 +/- 57 msec and mean dofetilide plasma concentration associated with half the maximum effect (EC50) was 2.2 +/- 0.6 ng/ml. Pharmacokinetic-pharmacodynamic modeling was useful in detecting the maximum effect and in describing the plasma concentration versus effect relationship during intravenous infusion of dofetilide but was otherwise not superior to analyses performed with postdistribution data.

CONCLUSION

We conclude that dofetilide prolongs QTc interval duration in a concentration-dependent manner in normal volunteers during sinus rhythm and that pharmacokinetic-pharmacodynamic modeling is useful for examination of maximum QTc prolongation induced by dofetilide.