This article is more than 5 years old. Information may no longer be current.
Acute upper respiratory tract infection may raise risk for excessive anticoagulation
Click Here to Manage Email Alerts
Patients taking warfarin who developed an upper respiratory tract infection were at increased risk for excessive anticoagulation, regardless of treatment with an antibiotic, researchers reported in a new study.
“The risk of excessive anticoagulation for individual antibiotics varied according to the interaction mechanism with the greatest risk presented by antibiotics interfering with warfarin metabolism,” the researchers wrote.
The retrospective, longitudinal cohort study analyzed patients receiving long-term warfarin who were seen at Kaiser Permanente Colorado from 2005 to March 31, 2011. Electronic, pharmacy and laboratory records were used to identify and classify three groups: patients with an upper respiratory tract infection co-prescribed warfarin and antibiotics (n=5,857); patients with an upper respiratory tract infection receiving long-term warfarin but no antibiotics (n=570); and healthy patients receiving warfarin only (n=5,579). The mean age of the patients was 68 years, and atrial fibrillation was the primary reason for anticoagulation therapy (44%).
The primary endpoint was the proportion of patients receiving an INR of at least 5 and change from pre-index INR to follow-up INR. The proportion of patients experiencing an INR of at least 5 was 3.2% in the antibiotic group, 2.6% in the warfarin-only group and 1.2% in the healthy group. The P values were <.001 for the antibiotic vs. healthy group, <.017 for the warfarin-only vs. healthy group and .44 for the antibiotic vs. warfarin-only group.
The researchers determined that predictors of an INR of at least 5 at follow-up included cancer diagnosis, female sex and elevated baseline INR. In contrast, an indication for warfarin of venous thromboembolism was associated with a lower likelihood of a follow-up INR of at least 5.
Analysis of different antibiotics revealed that those that interfered with warfarin metabolism were associated with the greatest risk for an INR of at least 5 compared with those that disrupted vitamin K synthesis or not previously reported to interact with warfarin (P<.001).
“Most patients in either the antibiotic or sick control groups did not have follow-up INRs that would have necessitated a change in the warfarin dosage, and similar 30-day rates of thromboembolism, bleeding and death were observed across all study groups,” the researchers wrote. “We conclude, therefore, that the absolute risk of harm associated with co-prescribing antibiotic and warfarin therapy is low.”
According to the researchers, the relationship between upper respiratory tract infection and excessive anticoagulation risk could be related to decreased food intake, particularly vitamin K-rich foods, and the effects of acetaminophen-containing cough and cold medications.
“Antibiotics also increase the risk. However, most patients with previously stable warfarin therapy will not experience clinically relevant increases in INR following antibiotic exposure or acute upper respiratory tract infection,” they wrote.
Disclosure: See the full study for a list of the researchers’ relevant financial disclosures.
Click Here to Manage Email Alerts