The effect of terfenadine on the cardiac pharmacodynamics of sparfloxacin.

This double-masked, randomized, placebo-controlled study was conducted to assess the effect of concomitant administration of terfenadine and sparfloxacin on the electrocardiographic (ECG) QT(c) interval in healthy volunteers, before the removal of terfenadine from the market. Eighty-eight men (aged 18 to 49 years, weighing 60.0 to 98.6 kg) with no clinically relevant ECG abnormalities received placebo, sparfloxacin (400 mg on day 1, 200 mg daily on days 2-4), terfenadine (60 mg BID), or the combination of sparfloxacin and terfenadine. After each dose, serial blood samples and ECG measurements were collected to determine sparfloxacin pharmacokinetic and pharmacodynamic variables. The area under the concentration-time curve and maximum concentration for sparfloxacin were approximately 16% less on day 4 compared with day 1, reflecting the higher plasma level after the 400-mg loading dose compared with that after the maintenance dose of 200 mg daily. Concomitant administration of terfenadine had no effect on these pharmacokinetic variables. When compared with the placebo-adjusted increases in QTc interval in the sparfloxacin (19 milliseconds on day 1 and 14 milliseconds on day 4) and terfenadine (2 milliseconds on day 1 and 7 milliseconds on day 4) treatment groups, the placebo-adjusted increases in QTc interval in the volunteers treated with the combination of sparfloxacin and terfenadine (18 milliseconds on day 1 and 22 milliseconds on day 4) were considered to be additive (no statistically significant interaction). Thus there are no apparent pharmacokinetic or dynamic QTc interactions between terfenadine and sparfloxacin. However, sparfloxacin should be administered with caution to patients receiving concomitant medications known to prolong the QTc interval.