Impact of Changes to In-hospital Drug Formularies on Out-of-hospital Prescription Rates and Cost: A Systematic Review.

Purpose: One of the main goals of an in-hospital drug formulary (in-HDF) is to modulate hospitalized patients' drug utilization. Theoretically, however, in-HDFs could also have an impact on out-of-hospital prescriptions in several ways, including discharged patients taking chronic medications that were initiated during hospitalization, hospital physicians prescribing to outpatients as if in-HDFs were equally applicable to the latter ("spillover effect"), and primary care physicians subsequently not changing such prescriptions ("induced prescription"). The aim of this study was thus to conduct a systematic review of papers that studied the impact of changes to in-HDF on out-of-hospital prescriptions.

Methods: We conducted a search of the PubMed and Embase databases. To be eligible for inclusion, studies had to be reported in English, Spanish, French, or Portuguese; as their designated aim, studies had to seek to evaluate the impact of a change in at least 1 active ingredient in the in-HDF on out-of-hospital prescriptions; and studies had to have at least 1 control period before the in-HDF change or a control group without any such change.

Findings: A total of 8 studies met the inclusion criteria: in 7 of these, out-of-hospital drug-utilization rates changed in line with the changes made to in-HDFs, with a decrease if the drug had been removed or restricted and an increase if the drug had been included and/or the opposite for competitor me-too medicines. Only 4 papers analyzed the impact on costs, half of which reported no statistically significant result.

Implications: Changes to in-HDFs have an impact on out-of-hospital prescription rates. Further studies are needed to examine the cost aspect since a research gap has been identified.