Background Assisted electronic prescribing system (EPS) is a tool with enormous potential for improving the safety of hospitalised patients. But it can also lead to medication errors (ME).

Purpose To assess the ME generated by an EPS during the medical prescription process.

Materials and methods Prospective study of two clinical inpatient units (internal medicine and haematology) in a general hospital, 4 months after an EPS was implemented (May and July 2010).

ME detected during pharmacist validation:

• ▶ Omission of allergies.

• ▶ Medication related errors (MRE): A) inadequate medication, B) inadequate pharmaceutical form (IPF), C) inadequate selection of medication (ISM) (drug not included in hospital formulary, when a formulary alternative existed), D) contraindicated drug (interaction), E) therapeutic duplication, F) omitted medication, G) not clear medication (NCM).

• ▶ Wrong dose.

• ▶ Wrong frequency of administration.

• ▶ Wrong way or route of administration (WRA).

• ▶ Wrong length of treatment.

Analysis of results: Excel database.

Results Average number of admitted patients was 25 patients/day (20–29). 177 ME were detected in 111 different patients, which mean an average of 4.4 errors/day and 1.5 errors/patient. Most of ME were due to discrepancies found between the prescription and observations stated by the doctor.

Conclusions Increasing medication safety and improving efficiency using EPS needs a culture change through a complex process, which involves physicians, pharmacists and nurses working as a team, as well as proper training of the EPS users of the EPS.