examined. The sample was made up of 134,637 patients ≥ 66 years of age taking warfarin for at least 180 continuative days. In this cohort, 45,972 subjects had received the prescription of at least one antibiotic. 2151 patients hospitalized for bleeding at the upper
gastrointestinal tract have been considered as active cases and, for each of them, 10 controls stratified according to age and sex, have been identified. Compared to these controls, active cases had received co-trimoxazole with a frequency of about 4 times higher (OR 3.84; IC 95%= 2.33-6.33). Even ciprofloxacin has been associated with an increase in bleedings (OR 1.94; IC 95% = 1.28-2.95), while there has been no significant association with amoxicillin, amplicillin, nitrofurantoin and norfloxacin.Co-trimoxazole is a drug still widely used in urinary infections and in other infections (for example, Staphylococcus-related skin infections and the ones connected to orthesis infections). It is opportune that itsuse, in older patients under anti-coagulation therapy, is avoided, as well as the use of ciprofloxacin. If this is not possible, INR must be
monitored during the antibiotic period, given the fact that bleeding risk increases considerably.
