Objectives -Data on the influence of acetaminophen intake on acute viral hepatitis is scarce, but it could play a role in the worsening of this disease. The aim of this study was to determine whether the intake of acetaminophen at therapeutic doses affects the severity of acute viral hepatitis. Methods -This was a prospective study concerning 37 consecutive patients hospitalized for acute viral hepatitis. Acetaminophen consumption and time since last intake were assessed by a questionnaire. Parameters of severity were studied in comparison to time related serum concentrations of acetaminophen. Results -Patients hospitalized for acute viral hepatitis (18 male, 19 female patients) had a mean age of 29.2 ±11.5 years. The causal virus was HAV (n = 23), HBV (n = 7) and other viruses (n = 8). The mean cumulated dose of acetaminophen was 7.7 ±5.65 g. The daily dose did not exceed the therapeutic dosage and the mean was 1.95 ±0.81 g (1-3 g). Patients who received 7.5 g of acetaminophen or more had a lower prothrombin index 52.4 ±30.3%vs 74.2 ±17.2%(P = 0.039), and a lower factor V 54.7 ±33.2%vs 83.3 ±19.6%(P = 0.033). Prothrombin index and bilirubinemia were negatively correlated with time related plasma acetaminophen concentrations. Conclusions -The use of acetaminophen at therapeutic doses was associated with greater alterations of surrogate markers of the severity of acute viral hepatitis especially hepatitis A. This was related to cumulated dosages and correlated to the time related acetaminophen plasma concentrations. Acetaminophen use should be interrupted when acute hepatitis is suspected. Objectives-Data on the influence of acetaminophen intake on acute viral hepatitis is scarce, but it could play a role in the worsening of this disease. The aim of this study was to determine whether the intake of acetaminophen at therapeutic doses affects the severity of acute Methods-This was a prospective study concerning 37 consecutive patients hospitalized for acute viral hepatitis. Acetaminophen consumption and time since last intake were assessed by a questionnaire. Parameters of severity were studied in comparison to time related serum concentrations of acetaminophen. Results - Patients were hospitalized for acute viral hepatitis (18 male, 19 female patients) had a mean age of 29.2 ± 11.5 years. The causal virus was HAV (n = 23), HBV (n = 7) and other viruses (n = 8). The mean cumulated dose of acetaminophen was 7.7 ± 5.65 g. The daily dose did not exceed the therapeutic dosage and the mean was 1.95 ± 0.81 g (1-3 g). Patients who received 7.5 g of acetaminophen or m (P = 0.039), and a lower factor V 54.7 ± 33.2% vs 83.3 ± 19.6% (P = 0.033). Prothrombin index and bilirubinemia were negatively correlated with time related plasma acetaminophen concentrations. The use of acetaminophen at therapeutic doses was associated with greater alterations of surrogate markers of the severity of acute viral hepatitis especially hepatitis A. This was related to cumulated microparticles dosages and correlated to the time related acetaminophen plasma concentrations. Acetaminophen use should be interrupted when acute hepatitis is suspected