Interaction between acetaminophen and warfarin in adults receiving long-term oral anticoagulants: a randomized controlled trial.

PURPOSE: We investigated whether acetaminophen, given at 2 g/day and 3 g/day might potentiate the anticoagulant effect of warfarin. METHODS: Forty-five patients on stable warfarin therapy, enrolled in this prospective, randomized, parallel (three arms), placebo-controlled study, received a 10-day regimen of acetaminophen (2 g/day or 3 g/day) or placebo. RESULTS: The mean maximal INR increase was 0.70 ± 0.49 and 0.67 ± 0.62 in patients receiving acetaminophen at 2 g/day and 3 g/day, respectively (P=0.01 for the respective comparisons versus placebo). The INR increase became significant on day 3 and was independently and significantly predicted by a maximal decrease in factor II (R(2)=0.36, P<0.0001), factor VII (R (2)=0.46, P<0.0001) and a maximal increase in acetaminophen plasma concentrations (R(2)=0.563, P<0.0001). CONCLUSION: Acetaminophen, at 2 g/day or 3 g/day, enhanced the anticoagulant effect of warfarin in stable patients, thus requiring close INR monitoring in the clinical setting.

[Use and misuse of intravenous drug administration in a department of internal medicine]. / Usage et mésusage de la voie intraveineuse pour l'administration de médicaments en médecine interne.

AIM: Numerous intravenously-administered medications are also available in equally effective oral forms. To assess the number of avoidable intravenous infusions, we retrospectively analyzed consecutive infusions prescribed in a department of internal medicine. METHODS: Between November and December 2004, we analyzed all patients who received at least one intravenous drug during hospitalization. Intravenous administration was considered unavoidable when prescribed for no more than 2 days in a patient unstable at admission, when oral administration or feeding was impossible, or when the drug was not available in oral form. RESULTS: During the study period 133 patients were admitted to the department. In all, 65 infusions were prescribed, 30% of which lasted more than 2 days for no medical reason. Four intravenous antibiotics were prescribed in patients when their antibiotic susceptibility tests indicated that another oral antibiotic could easily be given. Infusions for 16 other patients continued longer than 48 hours, although the oral route was not contraindicated in these patients and the medication was available in oral form. CONCLUSION: Systematic analysis of the daily prescriptions may be helpful in preventing or shortening use of intravenous medications and thereby decreasing iatrogenic infections and injuries, length of hospitalization, and costs.