Which antibiotics affect coumadin

As pharmacists, we find that certain questions about antibiotic prescribing and interactions come up with frequency. These questions often pertain to the use of warfarin, oral contraceptives, drugs that prolong the QT interval, and alcohol. But conflicting reports about issues such as monitoring international normalized ratio INR in patients taking warfarin and antibiotics, and whether or which antibiotics decrease the efficacy of oral contraceptives OCs can make decision-making challenging.

This review provides evidence-based answers to questions you may have. It also details some reliable sources of information you can consult TABLE 1 when discussing treatment options with other members of the health care team. Which antibiotics are preferable when a patient is taking warfarin, and are preemptive warfarin dose reductions advisable?

The simple answer is that agents with a lower likelihood of affecting the INR, such as penicillin G, clindamycin, and 1st- and 4th-generation cephalosporins, are a good place to start, and whether to preemptively reduce the warfarin dose hinges on the antibiotic being prescribed.

The more detailed answer. The fundamental mechanisms of interaction between warfarin and antibiotics are two-fold: 8. Clinical Pathways. Population Health. Public Safety. Wound Care. Publications Addiction Professional.

Behavioral Healthcare Executive. Cath Lab Digest. EP Lab Digest. IO Learning. Journal of Clinical Pathways. Journal of Invasive Cardiology. Podiatry Today. Psych Congress Network. The Dermatologist. Today's Wound Clinic. Vascular Disease Management. Advances in Inflammatory Bowel Disease.

Advances in Inflammatory Bowel Disease Regionals. AMP Europe. Amputation Prevention Symposium. Cape Cod Symposium on Addictive Disorders. Dermatology Week. EMS World Expo. An anticoagulant "blood thinner" , warfarin reduces blood's ability to clot. By preventing blood clots from forming in the brain, heart, legs, and lungs, warfarin lowers the risk of stroke, heart attack, and death.

Many antibiotics and related medications, including azole antifungal agents, heighten warfarin's blood-thinning ability and raise the risk of internal bleeding. Some antibiotics, such as rifampin, decrease warfarin's ability to "thin" the blood, increasing the risk a blood clot will form. People taking warfarin and antibiotics must be monitored closely. That's why if you are prescribed an antibiotic to treat or prevent an infection, you should immediately tell the clinician who manages your warfarin.

It is important to maintain a level of warfarin that is high enough to prevent unwanted blood clots without overly increasing the risk of bleeding," says Dr. Tejal Gandhi, associate professor of medicine at Harvard Medical School and an expert on outpatient drug safety.

In a recent study of 38, Medicare patients taking warfarin, researchers found that azole antifungals and all classes of antibiotics increased the risk of bleeding within two weeks, but to different degrees American Journal of Medicine, February The drug classes are listed in this chart, along with their risk of interaction 4. Warfarin levels are gauged by checking your prothrombin or clotting time, which is measured using the international normalized ratio INR. The higher the INR, the longer it takes for blood to clot.

If you take warfarin, an INR of 2 to 3 is often ideal, although the best range for you will be based on your individual condition. Antibiotics may cause this level to rise or fall, putting you in danger. At this level, the risk of gastrointestinal bleeding increases, and a bump on the head could become a bleed in the brain," says Dr.

The percentages of patients experiencing a follow-up INR of 5. The risk of an INR of 5. There was a numerically greater risk of a follow-up INR of 5. The percentage of patients with a follow-up INR greater than 3. Antibiotics interfering with warfarin metabolism were more likely to be associated with an INR of 5. There were patients with a body temperature recorded on the index date or within 7 days earlier, including Among patients with a recorded temperature, 7.

Factors independently associated with a follow-up INR of 5. In addition, patients with a preindex INR of 2. Limited methodologically rigorous research is available describing the nature and scope of the challenge presented when antibiotics are coprescribed with warfarin in clinical practice. Antibiotic group patients were also more likely to have a follow-up INR of 5. We identified that the likelihood of an INR of 5. Antibiotics inhibiting warfarin metabolism were more frequently associated with follow-up INRs of 5.

However, 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 day rates of thromboembolism, bleeding, and death were observed across all study groups. We conclude, therefore, that the absolute risk of harm associated with coprescribing antibiotic and warfarin therapy is low. Potential explanations as to why an upper respiratory tract infection without antibiotic prescription might increase the risk of excessive anticoagulation include reduced oral intake and resultant decreased consumption of vitamin K—rich foods, 14 the effect of acetaminophen-containing cough and cold remedies that can increase the INR, 15 , 16 or increased clotting factor catabolism associated with fever.

Previous studies 19 , 20 evaluating preemptive warfarin dosage reduction to mitigate the risk of excessive anticoagulation among patients prescribed antibiotics have reported mixed results.

Warfarin dosage reduction during trimethoprim-sulfamethoxazole coadministration resulted in fewer INRs higher than 4. Our study was strengthened by inclusion of a large number of real-world patients, uniform practice for addressing antibiotic prescriptions during warfarin therapy, thorough patient follow-up, and blinded independent adjudication of outcome events by multiple reviewers.

Carefully defined cohort designation and a run-in period of relatively stable warfarin therapy minimized background INR fluctuation that could have influenced the primary outcome. In some cases, out-of-range preindex INRs may have produced warfarin dosage changes increasing INR variability during follow-up. Reliance on ICD-9 codes for identification of clinically relevant bleeding and thromboembolic outcomes could have resulted in underestimation of these outcomes.

Deviations from this protocol that included a preemptive warfarin dose reduction could result in underestimation of the true interaction INR effect. However, if this scenario occurred, it was rare and unlikely to have significantly altered our observations.

Several baseline characteristics were significantly different between groups. Although these were included in the multivariable logistic regression analysis for the primary outcome of an INR of 5. We were unable to identify infection type within the antibiotic group. Different infections or infection locations could have resulted in varying risks for excessive anticoagulation. Finally, although the risk of an INR of 5.

Patients receiving warfarin who develop an acute upper respiratory tract infection are at increased risk of excessive anticoagulation with or without antibiotic exposure. 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. Characteristics associated with an increased risk of an INR of 5. Timely INR monitoring may be particularly important when one or more of these factors is present.

Studies are needed to determine whether less-frequent INR monitoring can be safely used during coadministration of antibiotics less likely to interact with warfarin therapy. Corresponding Author: Nathan P. Published Online: January 20, Author Contributions: Drs Clark and Delate had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

No other disclosures were reported. Our website uses cookies to enhance your experience. By continuing to use our site, or clicking "Continue," you are agreeing to our Cookie Policy Continue. View Large Download. Table 1. Baseline Characteristics by Group. Table 2. Frequency of Antibiotic Use. Table 3. Thirty-Day Outcomes by Study Group.

Table 4.