Significantly higher plasma haloperidol level during cotreatment with carbamazepine may herald cardiac change.

We investigated the effect of carbamazepine (CBZ) cotreatment with haloperidol (HP) on cardiac change in Japanese psychiatric patients without heart disease. Of 21 patients cotreated with CBZ, 11 showed lengthening of QT interval corrected for heart rate (QTc) (> 440, mean percentage change, 29), of whom two patients developed congestive heart failure because of left ventricular dysfunction. Especially in these two patients, plasma HP levels were significantly higher than speculated from the correlations. It is possible to speculate that, especially on CBZ cotreatment, significantly higher HP plasma level with QTc prolongation may herald heart failure.