OBJECTIVE: To report a case of fatal intracranial bleeding possibly due to an interaction between warfarin and inactivated influenza vaccination. CASE SUMMARY: A 64-year-old white male was admitted to the hospital after becoming unresponsive. The family reported a 2-day history of bleeding from the patient's rectum prior to admission. He had no recent changes in medical conditions or medication regimen, which included warfarin for stroke prophylaxis secondary to atrial fibrillation. The patient had received an inactivated influenza vaccine 4(1/2) weeks prior to presentation, at which time his international normalized ratio (INR) was 2.0. Upon admission, the patient's INR was greater than 15; INR values over the previous 6 months had been relatively stable (range 1.4-4.7). A noncontrast computed tomography scan of the head showed a large parenchymal hemorrhagic infarction involving the left temporal, parietal, and occipital lobes. In the emergency department, the patient received a nitroglycerin infusion to maintain systolic blood pressure in the range of 140-160 mm Hg as well as an infusion of 4 units of fresh frozen plasma and 10 mg of vitamin K. Following a neurosurgery evaluation, it was determined that nothing meaningful could be done to alter the patient's outcome positively, and he died approximately 17 hours after admission. DISCUSSION: To date, most reports of concomitant warfarin therapy and influenza vaccination indicate no significant change in average anticoagulation parameters. However, there are reports of individuals who may have experienced increased anticoagulation following influenza vaccination. The reason for these increases is unknown, but may involve only certain components of the vaccine, which is altered almost annually. Our patient's significant INR elevation, after being relatively stable for at least 6 months, was thought to be due to an interaction between warfarin and the influenza vaccination. The Horn Drug Interaction Probability Scale indicated a possible interaction between warfarin and the influenza vaccination. CONCLUSIONS: Considering the outcome in our patient, as well as outcomes in other individuals who have experienced an increased INR in a similar scenario, it appears justified to implement more frequent INR evaluations during the 4-6 weeks following influenza vaccination

BACKGROUND: Among millions of persons vaccinated against influenza virus each year, many are older patients treated with several drugs, including vitamin K antagonists (VKAs), among which warfarin is the most commonly used. Due to high interpatient and intrapatient variability, the therapeutic dose of VKA has to be individualized by monitoring of international normalized ratio (INR) values. The objectives of this study were to evaluate variation in the INR and warfarin weekly dose variation after influenza vaccination administration and to follow up patients for related hemorrhagic and thrombotic events to evaluate the safety of the influenza vaccine and to assess the immunogenicity of the influenza vaccination in patients receiving VKAs. METHODS: One hundred four patients on a stable VKA regimen and with an indication for influenza vaccination were randomized to receive influenza vaccination and subsequent placebo administration, or vice versa. All patients were tested for coagulation variables, clinical events, and antibody response against vaccine components. RESULTS: Similar mean prothrombin times, expressed as the INR and VKA weekly dose, were found in patients after receiving vaccine or placebo. The absence of any vaccination effect on VKA treatment was confirmed using a linear mixed-effects model. The percentages of time that patients were in therapeutic range were 70.7% after receiving vaccine and 72.4% after receiving placebo (P = .57). There were no fatal or major bleeding events and 11 minor mucocutaneous hemorrhagic events. After vaccination, the percentage of seroprotected patients ranged from 92.0% to 100.0% depending on the vaccine antigen examined. CONCLUSIONS: Influenza vaccination had no significant effect on INR values or warfarin sodium weekly doses. Close monitoring of INR values is not required after influenza vaccination in patients on stable long-term VKA regimens. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00222638

The effects on anticoagulation of a purified trivalent sub-unit influenza vaccine and a 14-valent pneumococcal vaccine were investigated in a single-blind controlled study involving 69 well-stabilised warfarin recipients. There were no clinically or statistically significant alterations of anticoagulant control in vaccine recipients as compared with controls at 2, 7 and 21 days after vaccination. On the basis of these data, concern about warfarin-vaccine interaction should not deter practitioners from immunising warfarin recipients against influenza or infection with Streptococcus pneumoniae

PURPOSE: The effect of influenza vaccination on oral anticoagulant control is uncertain but important to establish since anticoagulants are widely used and most patients taking them are candidates for immunisation because of age or underlying cardiac disease. We therefore prospectively evaluated the effect of influenza vaccination on International Normalised Ratio (INR) control in patients on long-term warfarin. METHODS: We undertook a prospective audit of patients on long-term warfarin attending a single hospital anticoagulant clinic who reported receiving influenza vaccination within the 10 days prior to a clinic visit. We compared the stability of anticoagulant control in the 12 months prior to and 10 days after immunisation, restricting analysis to those patients whose warfarin dosage was unchanged before and after vaccination. RESULTS: Of 106 consecutive patients who reported receiving influenza vaccination within the 10 days prior to a clinic visit, results were evaluable in 78 because the dose of warfarin was unchanged before and after vaccination. Influenza immunisation had no apparent effect on anticoagulant control. No bleeding or thrombotic complications were reported. CONCLUSIONS: Our findings suggest that it is not necessary to routinely monitor the INR more closely after influenza vaccination

PURPOSE: Warfarin is commonly used among patients who receive influenza, pneumococcal, and tetanus and diphtheria toxoid vaccines, and persons on warfarin therapy may also receive Hepatitis A vaccine. There has been concern that vaccinations could potentially alter coagulation parameters in patients on warfarin therapy. We sought to determine whether vaccinations are associated with changes in International Normalized Ratio (INR) in persons on long-term warfarin therapy. METHODS: We conducted a retrospective cohort study of 5167 members of Group Health, a health maintenance organization (HMO) in western Washington State, who were aged 18 years and older and who were on stable long-term warfarin therapy between 1 January 1992 and 31 December 2003. We made within-person comparisons between mean INR values in the 28 days after receipt of influenza, pneumococcal, tetanus, or hepatitis A vaccine versus mean INR values during other times. RESULTS: Receipt of influenza vaccine was not associated with a change in INR value (mean change, 0.01; 95% confidence interval (CI) -0.01 to 0.03); similar results were observed for pneumococcal (mean change 0.01; 95%CI -0.07 to 0.09), tetanus (mean change 0.03; 95%CI -0.03 to 0.10), and hepatitis A vaccines (mean change 0.03; 95%CI -0.10 to 0.14). CONCLUSIONS: Our results do not suggest that vaccinations lead to clinically significant alterations in coagulation measures among adults on chronic warfarin therapy