Abstract
Background
Drug interactions with warfarin are common and may be responsible for increased patient
morbidity and treatment costs.
Objectives
To assess the usage patterns of drugs that potentiate warfarin's anticoagulant activity
and discuss their associated relationship with both risk of hemorrhage and treatment
costs among warfarin users with atrial fibrillation (AF).
Methods
A nested case–control study of long-term warfarin-treated AF patients was conducted
using a health insurance claims database. Patients with a hemorrhagic event (cases)
were matched to control patients using the incidence density sampling method. Drug-potentiating
warfarin effects were identified within 30 days before the hemorrhagic event. Conditional
logistic regression was used to calculate the association between use of potentiating
drugs and hemorrhage risk. Mean treatment costs and CIs were calculated using the
bootstrap method and tested using the t-test. Factors associated with treatment costs were determined using generalized linear
models with the log-link function and γ distribution.
Results
Approximately 80% of AF patients were prescribed at least 1 warfarin-potentiating
medication while taking warfarin. Patients who used these medications had a 26% higher
risk of hemorrhage compared with those who did not use these drugs. Likelihood of
hemorrhagic events was significantly increased with the use of potentiating drugs
from the following therapeutic classes: anticoagulants (odds ratio [OR] = 1.91), anti-infectives
(OR = 1.76), antiplatelets (OR = 1.56), and analgesics (OR = 1.33). The risk also
increased when patients took ≥3 therapeutic classes of interacting medications (OR
= 1.62–1.85). Among patients with a hemorrhagic event, patients who were prescribed
potentiating drugs had higher hemorrhage-related treatment costs ($1359) compared
with those patients without prescriptions for warfarin-potentiating drugs ($691; P < 0.001).
Conclusions
Warfarin-potentiating drugs were commonly used among AF patients on warfarin. The
use of potentiating drugs increased the risk of a hemorrhage, leading to higher treatment
costs. More frequent monitoring or alternative anticoagulant therapies are needed
to avoid frequent warfarin drug interactions.
Keywords
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Article info
Publication history
Published online: June 21, 2012
Accepted:
May 23,
2012
Identification
Copyright
© 2012 Elsevier HS Journals, Inc. Published by Elsevier Inc. All rights reserved.
