The influence that electronic prescribing has on medication errors and preventable adverse drug events: an interrupted time-series study.

Objective: This study evaluated the effect of a Computerized Physician Order Entry system with basic Clinical Decision Support (CPOE/CDSS) on the incidence of medication errors (MEs) and preventable adverse drug events (pADEs).

Design: Interrupted time-series design.

Measurements: The primary outcome measurements comprised the percentage of medication orders with one or more MEs and the percentage of patients with one or more pADEs.

Results: Pre-implementation, the mean percentage of medication orders containing at least one ME was 55%, whereas this became 17% post-implementation. The introduction of CPOE/CDSS has led to a significant immediate absolute reduction of 40.3% (95% CI: -45.13%; -35.48%) in medication orders with one or more errors. Pre-implementation, the mean percentage of admitted patients experiencing at least one pADE was 15.5%, as opposed to 7.3% post-implementation. However, this decrease could not be attributed to the introduction of CPOE/CDSS: taking into consideration the interrupted time-series design, the immediate change was not significant (-0.42%, 95% CI: -15.52%; 14.68%) because of the observed underlying negative trend during the pre-CPOE period of -4.04% [95% CI: -7.70%; -0.38%] per month.

Conclusions: This study has shown that CPOE/CDSS reduces the incidence of medication errors. However, a direct effect on actual patient harm (pADEs) was not demonstrated.