Intramuscular route for the administration of the anti-flu vaccine in patients receiving oral anticoagulation therapy

Comparison of safety and effectiveness of the intramuscular (IM) (deltoid) vs subcutaneous (s.c.) administration of the flu vaccine (FV) in patients on oral anticoagulation therapy. It was a phase IV, simple blind, 2-parallel groups, randomized trial developed in an urban primary care setting. We included patients taking oral anticoagulation therapy without FV contraindications. The IM administration of the FV in the experimental group was compared with a SC administration in the control group. 59 patients were included. The two groups were comparable at the beginning of the study. INR was not modified following s.c. (p = 0.38) or i.m. (p = 0.49) administration. No systemic side effects were observed. More cutaneous lesions were observed in the S.C. group (71.4%) when compared with the i.m. group (25.8%; p < 0.0001). For the remaining variables, we observed a tendency towards more reported pain in the SC group (35.7 vs 22.6%) and a larger brachial diameter (42 vs 29%) without significant differences. 3.2% of patients in the i.m. group and 7.1% in the s.c. group developed influenza symptoms without significant differences. Even though the results must be interpreted with caution, currently there appears to be no apparent contraindication for the i.m. administration of the FV. When it is administered subcutaneously, it tends to cause more side effects.