The effect of antibiotic coadministration on the international normalized ratio (INR) in a relatively stable, real-world warfarin population has not been adequately described. Case reports and studies of healthy volunteers do not account for the potential contribution of acute illness to INR variability.OBJECTIVE To compare the risk of excessive anticoagulation among patients with stable warfarin therapy purchasing an antibiotic (antibiotic group) with the risk in patients purchasing a warfarin refill (stable controls) and patients with upper respiratory tract infection but not receiving an antibiotic (sick controls).

An interactive voice response phone call and follow-up letter significantly improved primary adherence to oral bisphosphonate therapy. Such an intervention could be considered for improving primary adherence rates to other medication classes.

Internal funding was provided by the Department of Pharmacy at Kaiser Permanente Colorado. There are no external funding sources to disclose. Riggs, Milchak, Patel, and Heilmann are employed by Kaiser Permanente Colorado. The authors report no other potential conflicts of interest. Study concept and design were contributed by Riggs, Heilmann, and Billups, along with the other authors. Billups collected the data, and data interpretation was performed by Riggs, Milchak, and Flores, with assistance from the other authors. The manuscript was written primarily by Riggs, along with Flores, and revised by Billups, Milchak, Patel, and Heilmann.