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

Background: 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.

Objective: 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.

Methods: 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.

Results: 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.

Conclusions: 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.