Effects of electronic prescribing on formulary compliance and generic drug utilization in the ambulatory care setting: a retrospective analysis of administrative claims data.

OBJECTIVE Electronic prescribing (e-prescribing) provides formulary information at the point of care. The objective of this study was to assess the effects of e-prescribing on formulary compliance and generic utilization. METHODS This was a retrospective analysis of pharmacy claims data from a large national managed care organization. A sample of 95 providers using predominantly e-prescribing was randomly selected (e-prescriber group). A matched sample of 95 traditional prescribers was selected (traditional prescriber group), matched to the e-prescriber group by zip code and medical specialty. A total of 110,975 paid pharmacy claims, for the 12 months from August 1, 2001, through July 31, 2002, were analyzed to assess the effect of e-prescribing on formulary compliance and generic utilization. All paid pharmacy claims were examined for each group; for the e-prescriber group, this included all claims, not just those prescribed using an e-prescribing device. A written qualitative survey was distributed to physicians and office managers to assess e-prescribing usage, sources of formulary information, and effects of e-prescribing on office resources. RESULTS Both predominantly e-prescribers and traditional prescribers demonstrated high levels of formulary compliance, 83.2% versus 82.8%, respectively (P=0.32). Formulary compliance for these groups did not differ from the overall prescriber population (82.0%). There was not a difference in generic drug utilization rates between e-prescribers and traditional prescribers (absolute rates 37.3% versus 36.9%, P=0.18). Qualitative survey responses supported previously reported research indicating reductions in calls both to and from pharmacies for prescription orders. CONCLUSIONS An examination of paid pharmacy claims from a large, national managed care organization demonstrated no differences between predominantly e-prescribers and traditional prescribers in measures of formulary compliance or generic drug utilization. Future studies should examine keystroke data at the point of care to observe more detail about drug selection methods.