Frequency, types, and potential clinical significance of medication-dispensing errors

Many dispensing errors occur in the hospital, and these can endanger patients. The purpose of this study was to assess the rate of dispensing errors by a unit dose drug dispensing system, to categorize the most frequent types of errors, and to evaluate their potential clinical significance.

A prospective study using a direct observation method to detect medication-dispensing errors was used. From March 2007 to April 2007, 'errors detected by pharmacists' and 'errors detected by nurses' were recorded under six categories: unauthorized drug, incorrect form of drug, improper dose, omission, incorrect time, and deteriorated drug errors. The potential clinical significance of the 'errors detected by nurses' was evaluated.

Among the 734 filled medication cassettes, 179 errors were detected corresponding to a total of 7249 correctly fulfilled and omitted unit doses. An overall error rate of 2.5% was found. Errors detected by pharmacists and nurses represented 155 (86.6%) and 24 (13.4%) of the 179 errors, respectively. The most frequent types of errors were improper dose (n = 57, 31.8%) and omission (n = 54, 30.2%). Nearly 45% of the 24 errors detected by nurses had the potential to cause a significant (n = 7, 29.2%) or serious (n = 4, 16.6%) adverse drug event.

Even if none of the errors reached the patients in this study, a 2.5% error rate indicates the need for improving the unit dose drug-dispensing system. Furthermore, it is almost certain that this study failed to detect some medication errors, further arguing for strategies to prevent their recurrence.