Background Medication errors represent an important problem of patient safety and have consequences on healthcare services. The authors used an observational national multicentre study to monitor the medicines use process in wards as a tool to control and to prevent these incidents.

Purpose To improve the medicines use process in our tertiary hospital.

Materials and methods The authors first conducted a prestudy to estimate the rate of medication errors in our hospital. In the light of this rate the authors calculated the number of observations required to obtain a representative sample of the population studied. At the same time, The authors checked the prescription validation process in the pharmacy as well as the initial process for prescribing medicines. Then during the months of April–September 2011, the authors performed a prospective, observational, not-disguised study using the modified Barker–McConnell method. The authors observed nurses from when they were preparing patient medicines until administration in the patient's room to detect opportunities for error. The study included all the wards open during this period. Each drug administered to a patient was reported as an observation. Thus, The authors evaluated the complete medicines use process.

Results The authors performed 1167 observations in 297 patients (52.2% were women). The mean age was 72.1 (SD 15.4) (ranges 17–98). 34.1% of patients were over the age of 80. The error rate was 14.8% (173 errors/1167 observations). The distribution of 173 medication errors detected was as follows: 45.1% omission, 19.6% time error, 8.6% wrong method or administration rate, 6.4% drug not prescribed, 5.7% incorrect dosage (less), 5.2% no nurse checking, 2.3% prescription error and 7.1% others. The most frequently omitted group of drugs was analgesics.

Conclusions The observational method used to monitor drug administration by nurses revealed itself as a good system to study the present state of the medicines use process in the hospital. It helped to identify weak points in the process which should be modified and establish strategies for preventing medication errors and improving patient safety.