Objectives The growing number of drugs on the market makes it necessary to adapt hospital formularies in order to ensure consistent drug coverage. The aim of this study was to evaluate the impact of the prescription of non-formulary drugs (NFD) on the therapeutic management of admitted patients.

Methods This retrospective observational study included NFD prescriptions in patients hospitalised in a tertiary university hospital during the period 2012–2015. NFD prescriptions are displayed on the computerised medical order as a pending alert to be reviewed by the clinical pharmacists, who make a notation to the clinical course that includes a recommendation for an available therapeutic alternative when available in the hospital formulary. The degree of acceptance of the recommendation by physicians is recorded.

Results Approximately 0.5% of patients hospitalised during the study period were affected by an NFD prescription. A total of 52 (9.5%) NFD were of doubtful therapeutic efficacy, five (0.9%) were non-replaceable drugs and 490 (89.4%) were prescriptions for drugs with an alternative available in the hospital formulary. The acceptance rate for the recommended alternative was 34.9% in the evaluable NFD prescriptions. No correlation was observed between the number of NFD prescriptions or the number of NFD and the availability index (drugs included in the hospital formulary in relation to the total number of drugs marketed).

Conclusions The number of patients with a NFD prescription was very low. The lack of correlation between the number of NFD or NFD prescriptions and the availability index demonstrated that the hospital formulary covers practically all therapeutic needs.