Lack of effect of influenza immunisation on anticoagulant control in patients on long-term warfarin.
OBJECTIVE
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.
MacCallum
Peter
P
Department of Haematology, Barts and The London NHS Trust, London, UK. p.k.maccallum@qmul.ac.uk
Madhani
Manisha
M
Mt-Isa
Shahrul
S
Ashby
Deborah
D
D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology*; D001777:Blood Coagulation / Q000187:drug effects; D004347:Drug Interactions; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced; D006801:Humans; D007252:Influenza Vaccines / Q000009:adverse effects / Q000494:pharmacology*; D019934:International Normalized Ratio; D008297:Male; D010044:Outpatient Clinics, Hospital; D011446:Prospective Studies; D013927:Thrombosis / Q000517:prevention & control; D014859:Warfarin / Q000494:pharmacology*
D000925:Anticoagulants; D007252:Influenza Vaccines; D014859:Warfarin