Poor adherence as a potential source of poor anticoagulation control

Seikeng Koh, M.Pharm^*, Edith A. Nutescu, Pharm D
April, 2007

Reference: Kimmel SE, Chen Z, Price M, Parker CS, Metlay JP,Christic JD et al. The influence of patient adherence on anticoagulation control with warfarin: results from the international normalized ratio adherence and genetics (IN-RANGE) study. Arch Intern Med 2007; 167: 229-235.

Major Point:

Patients with poor adherence to their warfarin therapy have poor anticoagulation control even if they are being managed in specialized anticoagulation clinics.

Summary:

The international normalized ratio adherence and genetics (IN-RANGE) study was a prospective cohort study of 136 patients conducted in 3 anticoagulation clinics and over a period of 32 weeks looking into the impact of warfarin adherence and genetic variability on anticoagulation control. This first report (reviewed here) looked into the adherence factor affecting anticoagulation control. The medication event monitoring system (MEMS) was used to track timing of medication use. The number of incorrect warfarin dose days, over adherent and under adherent days and INR at each visit were calculated. A total of 1490 INR measurements were taken; 40.4% of them were out of range with 25.8% below and 14.6% above the target range. Under anticoagulation was more likely associated with patients who refused to use the MEMS caps (p=0.006) and were noncompliant to their warfarin therapy (p<0.001). Missing 1 to 2 doses a week (20%-30% missed doses) was associated with up to a 2-fold increased odds of sub therapeutic anticoagulation. Over adherence was associated with over-anticoagulation but not under anticoagulation. Neither the phase of therapy (initiation vs maintenance, p>0.5) nor the length of interval between visits (p>0.10) had an impact on the INR-adherence associations. The authors concluded that poor adherence was a potential course of poor anticoagulation control even if the patients were managed by anticoagulation clinics where the importance of adherence was constantly emphasized.

^*Seikeng Koh is a pharmacist with the Singapore General Hospital who is currently doing an anticoagulation rotation with Dr. Edith Nutescu at the Antithrombosis Unit, UIC.