RT Journal
A1 Hylek EM
T1 ACetaminophen and risk factors for excess anticoagulation with warfarin—reply
JF JAMA
JO JAMA
YR 1998
FD August 26
VO 280
IS 8
SP 695
OP 697
DO 10-1001/pubs.JAMA-ISSN-0098-7484-280-8-jbk0826
UL http://dx.doi.org/10-1001/pubs.JAMA-ISSN-0098-7484-280-8-jbk0826
AB 
In a closely monitored setting, INR values higher than 6 are unusual and occur in only about 1% of tests in our anticoagulant therapy unit among patients who have been receiving warfarin for more than 1 month and whose target INR was 2 to 3. The large number of patients managed by our anticoagulant unit provided enough cases with an INR higher than 6 (n=93) to assess simultaneously several apparent risk factors. The relationship we observed between acetaminophen intake and an INR higher than 6 was strong and dose dependent and remained significant in the presence of other factors, as assessed by multivariate modeling. Such attributes weigh in favor of a causal relationship, but our study design cannot prove causality, particularly in the context of complex medical patients.