Lack of effect of influenza vaccine on anticoagulation by acenocoumarol

OBJECTIVE: To analyze the effects of influenza vaccine on patients receiving chronic anticoagulant therapy with acenocoumarol. DESIGN: A prospective trial. SETTING: Hospital de la Santa Creu i Sant Pau, Barcelona. PATIENTS: Forty-three patients who received acenocoumarol, had stable levels of International Normalized Ratio (INR), and did not need dosage modification for four months before entering the study. INTERVENTION: A study of anticoagulation levels measured by INR at 7, 15, and 30 days from administration of the trivalent vaccine from the 91-92 campaign was conducted. MAIN OUTCOME MEASURES: Comparison was made between basal values (day 0) and anticoagulation levels at 7, 15, and 30 days from vaccine administration by means of a repeated-measures ANOVA. RESULTS: Nine patients (21 percent) had INR levels out of the therapeutic range during the study period. INR increased in three of these patients and decreased in six. There were no significant intraindividual changes in INR values during the time period analyzed (p = 0.125). No hemorrhagic or thrombotic manifestations occurred and no significant changes in renal or hepatic biochemistry were observed. CONCLUSIONS: Influenza vaccine does not modify acenocoumarol activity in patients receiving long-term anticoagulant therapy.