Fig. 4. Concentration–effects relations on corrected QT interval prolongation of 1 mg droperidol (  A ) and 4 mg ondansetron (  B ) administered alone in a crossover study of 16 healthy volunteers. Only postdistribution concentrations are shown. The linear regression was significant with droperidol (  r = 0.34,  P = 0.005) but not with ondansetron (  r = 0.16,  P = 0.26).  Continuous lines represent the linear regression with the 95% prediction band.