Background
Prescribing errors are a common cause of harmto patients. Electronic prescribing is a new intervention which can reduce , but does not abolish, prescribing errors1. There is a need to understand the causes of the errors which remain in order to make recommendations for their prevention. This study investigated the causes of prescribing errors occurring with an electronic prescribing, dispensing and medication administration system (ServeRx; MDG Medical) on a surgical ward. We used a qualitative methodology similar to that used in a previous study of prescribing errors2, and classified ied errors according to a model of accident causation3.

Methods
Pharmacists were authorised to transcribe medication orders on the study ward, and were included in the study. Eleven prescribers who had made errors, including three pharmacists and eight junior doctors, were interviewed using a semi-structured approach with open questions, to investigate their perceptions of the causes of the errors. Themes arising from the interviews were classified according to Reason's model of accident causation, into active failures, error-producing conditions, latent conditions and failures in defences.

Results
The majority of errors in this study were rule-based mistakes or skill-based slips, although lapses in attention also occurred. A variety of error-producing conditions contributed to errors, including workload, communication, training and experience. Latent conditions identified included beliefs about individual drugs, and beliefs about the functions of electronic prescribing systems. A number of themes were identified relating to weaknesses in the computer system as a defence, including incorrect default settings, the method of prescribing on the computer, the layout of screens and menus, and the training of staff to use the system.

Discussion
Recommendations for preventing errors in electronic prescribing systems include d improving training in both prescribing (particularly for pharmacists, for whom the task of prescribing is relatively new), and in use of the computer system. Systems should be implemented in a way that minimises unnecessary transcribing, and prescribers should be made aware of the functions and limitations of computerised prescribing systems.