The prevalence of drug omissions is often underestimated but their impact can be clinically relevant. We hypothesized that delays in the administration of non-formulary/non-stored drugs could impair the quality of care. The aims of this study were:

– to determine the time between the prescription and the administration of the first prescribed dose and, if applicable, to calculate how many doses were omitted;

– to analyze the clinical relevance of the identified delays.

Three months retrospective study of electronic records of patients hospitalized on the internal medicine wards of a network of hospitals supplied by a centralized pharmacy. This pharmacy is located in one of the sites; other sites are 15–45km apart.

Main outcome measures:

– for the main hospital site and the three distant sites:

– median time between the prescription and the administration of the first prescribed dose,

– mean number of omitted doses for formulary and non-formulary/non-stored drugs,

– categorization of patient's harm caused by the delays of time-critical drugs, according to the NCC-MERP taxonomy of medication errors.

In all, 16,954 prescriptions were analyzed. Calculated delays for non-stored/non-formulary drugs were longer than for formulary drugs. However, the median time to administration is less than 1hour for both formulary and non-stored/non-formulary drugs; and more than 95% of formulary drugs and around 90% of non-stored/non-formulary drugs were administered within 24h following their prescription. There was no significant difference in the mean number of omitted doses or in the delays between the site where the centralized pharmacy is located and the other sites, except for one of them. A delay representing 1.5 or more omitted doses were found for 332 (1.96%) prescriptions. Among them, only 17 were considered potentially clinically relevant. None of them caused severe harm to the patients involved.

In our setting, non-stored/non-formulary drugs take more time to be delivered than formulary drugs, but more than 95% of formulary drugs and around 90% of non-stored/non-formulary drugs are administered within 24h following their prescription. None of the 17 patients who experienced delays underwent severe harm. Our study showed that delays also occur for formulary drugs but no systematic cause of omission was identified; further studies should focus on all dose omissions during hospitalization.