The frequency and potential causes of dispensing errors in a hospital pharmacy

To determine the frequency and types of dispensing errors identified both at the final check stage and outside of a UK hospital pharmacy, to explore the reasons why they occurred, and to make recommendations for their prevention.

A definition of a dispensing error and a classification system were developed. To study the frequency and types of errors, pharmacy staff recorded details of all errors identified at the final check stage during a two-week period; all errors identified outside of the department and reported during a one-year period were also recorded. During a separate six-week period, pharmacy staff making dispensing errors identified at the final check stage were interviewed to explore the causes; the findings were analysed using a model of human error.

Percentage of dispensed items for which one or more dispensing errors were identified at the final check stage; percentage for which an error was reported outside of the pharmacy department; the active failures, error producing conditions and latent conditions that result in dispensing errors occurring.

One or more dispensing errors were identified at the final check stage in 2.1% of 4849 dispensed items, and outside of the pharmacy department in 0.02% of 194,584 items. The majority of those identified at the final check stage involved slips in picking products, or mistakes in making assumptions about the products concerned. Factors contributing to the errors included labelling and storage of containers in the dispensary, interruptions and distractions, a culture where errors are seen as being inevitable, and reliance on others to identify and rectify errors.

Dispensing errors occur in about 2% of all dispensed items. About 1 in 100 of these is missed by the final check. The impact on dispensing errors of developments such as automated dispensing systems should be evaluated.