Effects of a hospital formulary on outpatient drug switching

• Objective: To assess the effect of an inpatient formulary on outpatient medication use. • Design: Retrospective analysis of claims and administrative data. • Setting and participants: Members of 2 capitated health care plans admitted to an academic tertiary care hospital in 2001-2002 who were using a proton pump inhibitor (PPI) or statin not on the hospital formulary within 3 months prior to hospitalization. • Measurements: The primary outcome was postdischarge use of a hospital formulary PPI or statin. • Results: In 2001-2002, there were 139 patients who accounted for 177 admissions. There were 192 cases of nonformulary, preadmission use of a PPI or statin. A PPI or statin was ordered during hospitalization in 22% (95% confidence interval [CI], 16%-28%) of eligible cases; virtually all of these patients received the inpatient formulary equivalent. A discharge prescription for a formulary PPI or statin was given in 8% (95% CI, 4%-11%) of eligible cases, although only 1 patient (0.5%; 95% CI, 0%-2%) filled such a prescription. • Conclusion: These data suggest that an inpatient formulary has minimal effect on outpatient PPI or statin drug switching in a privately insured, managed care population.