Examination of baseline risk factors for QTc interval prolongation in patients prescribed intravenous haloperidol

Intravenous haloperidol can increase the risk for corrected QT interval (QTc) prolongation, torsades de pointes (TdP) and sudden death. There are a number of risk factors reported in the literature for QTc prolongation and TdP with intravenous haloperidol.

The purpose of this study was to determine the prevalence of baseline risk factors for QTc prolongation and TdP in hospitalized medical inpatients prescribed intravenous haloperidol.

This is a retrospective cohort study of medically ill hospitalized inpatients prescribed intravenous haloperidol between 30 June 2007 and 1 January 2010. Records were ascertained for the presence of baseline risk factors for QTc prolongation and TdP.

A total of 175 subjects were identified as receiving intravenous haloperidol during the study period. Mean age was 62.9 ± 19.1 years, and 48.6% of subjects were female. At baseline, 85.7% of subjects had ≥1 risk factor for QTc prolongation and TdP, with the majority of these subjects (58.0%) having between two and five risk factors. Of the total study sample, 74.9% had a baseline ECG; mean QTc value was 457 msec (± 40.8 msec). Greater than 50% of subjects had a sex-specific QTc value higher than the increased risk threshold of 450 msec in males or 460 msec in females at baseline. Following intravenous haloperidol administration, 46.9% of subjects had a follow-up ECG obtained within 24 hours. At the time of intravenous haloperidol administration, 93.1% of subjects had a potassium value available and 62.9% had a magnesium value. Approximately 30% of subjects had either a potassium or magnesium value below the normal laboratory range. Of the 175 subjects, 43.4% were taking ≥1 concomitant QTc prolongation medication at the time of intravenous haloperidol administration.

Consistent with previously published reports, patients in this study prescribed intravenous haloperidol had multiple risk factors, both modifiable and non-modifiable, at baseline for QTc prolongation and TdP. The modifiable risk factors may be important targets of interventions aimed at optimizing the safety of the use of intravenous haloperidol, while the non-modifiable risk factors may warrant closer scrutiny with consideration of alternative therapies and continuous monitoring.