Objectives Improvements in a hospital's medication administration process might reduce the prevalence of medication errors and improve patient safety. The objective of this study was to evaluate the success of an automated medication system in reducing medication administration errors.

Methods A controlled before-and-after study with follow-up after 4 months was conducted in two Danish haematological hospital wards. The occurrence of administration errors was observed in two 3-week periods. The error rate was calculated by dividing the number of doses with one or more errors by the number of doses (opportunities for errors). Logistic regression was used to assess changes in error rates after implementation of the automated medication system with time, group, and interaction between time and group as independent variables. The estimated parameter for the interaction term was interpreted as the incremental change (‘difference-in-difference’) caused by the new dispensing system.

Results A total of 697 doses with one or more errors were identified out of 2245 doses. The error rate decreased from 0.35 at baseline to 0.17 at follow-up in the intervention ward and from 0.37 to 0.35 in the control ward. The overall risk of errors was reduced by 57% in the intervention ward compared with the control ward (OR 0.43; 95% CI 0.30 to 0.63).

Conclusions The automated medication system reduced the error rate of the medication administration process and thus improved patient safety in the medication process.