Randomized evaluations of the impact of acetaminophen on the pharmacodynamics of warfarin
| Study, period . | Study size . | Acetaminophen dose . | Study outcome . |
|---|---|---|---|
| Antlitz,16 1968 | 20 | 650 mg vs placebo for 2 doses | No significant difference in prothrombin times between acetaminophen and placebo during the 48-hour period after 2 doses of study drug. |
| Mahé,17 2004 | 11 | 4 g/d vs placebo for 14 d | The mean observed INR was significantly increased after 4 days in the acetaminophen group. The mean maximum INR observed was 3.47 in the acetaminophen arm and 2.61 in the placebo arm (P = .001). The mean maximum increase in the INR was 1.04 (acetaminophen group) versus 0.20 (placebo group; P = .003). |
| Mahé,18 2006 | 20 | 4 g/d vs placebo for 14 d | The mean maximum INR observed was 3.45 in the acetaminophen arm and 2.66 in the placebo arm (P = .03). The mean maximum increase in the INR was 1.20 (acetaminophen group) versus 0.37 (placebo group; P < .001). Significant reductions in the vitamin K-dependent clotting factors II, VII, IX, and X accompanied the increase in INR. |
| Parra,19 2007 | 36 | 2 g/d, 4 g/d; vs placebo for 4 wk | At week 2, the 2 g/d group had significantly higher INR compared with placebo (P = .01). At weeks 1, 2, and 3, the 4 g/d group had significantly higher INR than placebo (P = .04, P = .01, and P = .01, respectively). |
| Zhang,20 2011 | 45 | 2 g/d, 3 g/d; vs placebo for 10 d | The mean INR increase was 0.70, 0.67, and 0.14 in the 2 g/d group, 3 g/d group, and in the placebo group, respectively (P = .01). Factor VII levels were lower in the acetaminophen groups compared with placebo, but not levels of factors II and V. |
| Study, period . | Study size . | Acetaminophen dose . | Study outcome . |
|---|---|---|---|
| Antlitz,16 1968 | 20 | 650 mg vs placebo for 2 doses | No significant difference in prothrombin times between acetaminophen and placebo during the 48-hour period after 2 doses of study drug. |
| Mahé,17 2004 | 11 | 4 g/d vs placebo for 14 d | The mean observed INR was significantly increased after 4 days in the acetaminophen group. The mean maximum INR observed was 3.47 in the acetaminophen arm and 2.61 in the placebo arm (P = .001). The mean maximum increase in the INR was 1.04 (acetaminophen group) versus 0.20 (placebo group; P = .003). |
| Mahé,18 2006 | 20 | 4 g/d vs placebo for 14 d | The mean maximum INR observed was 3.45 in the acetaminophen arm and 2.66 in the placebo arm (P = .03). The mean maximum increase in the INR was 1.20 (acetaminophen group) versus 0.37 (placebo group; P < .001). Significant reductions in the vitamin K-dependent clotting factors II, VII, IX, and X accompanied the increase in INR. |
| Parra,19 2007 | 36 | 2 g/d, 4 g/d; vs placebo for 4 wk | At week 2, the 2 g/d group had significantly higher INR compared with placebo (P = .01). At weeks 1, 2, and 3, the 4 g/d group had significantly higher INR than placebo (P = .04, P = .01, and P = .01, respectively). |
| Zhang,20 2011 | 45 | 2 g/d, 3 g/d; vs placebo for 10 d | The mean INR increase was 0.70, 0.67, and 0.14 in the 2 g/d group, 3 g/d group, and in the placebo group, respectively (P = .01). Factor VII levels were lower in the acetaminophen groups compared with placebo, but not levels of factors II and V. |
INR indicates international normalized ratio.