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J Korean Soc Emerg Med > Volume 14(1); 2003 > Article
Journal of The Korean Society of Emergency Medicine 2003;14(1): 56-60.
The Clinical Use of the Plasma Acetaminophen Halflife in NAC-treated Acetaminophen Overdose
Seung Ho Lee, Mi Jin Lee, Woon Jeung Lee, Won Jae Lee, Se Kyung Kim
Department of Emergency Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea. emmam@catholic.ac.kr
A plasma acetaminophen halflife of more than 4 hours has been correlated with hepatotoxicity in acetaminophen overdosing not treated with an antidote. However, the acetaminophen halflife has not been studied in patients receiving the antidote N-acetylcysteine (NAC).
Ninety-eight (98) patients with acetaminophen overdoses, all of whom were treated with N-acetylcysteine were studied. A minimum of 2 plasma acetaminophen valu e s > 2.0 microgram/ml were available for calculating the acetaminophen halflife, assuming first-order kinetics.
Overall, the median acetaminophen halflife was 6.2 hours (range, 1.15~103.9 hours). Sixty-two (62) patients with no hepatotoxicity (AST < 100 U/L), 13 patients with little hepatotoxicity (100 U/L < AST < 1,000 U/L), 17 patients with severe hepatotoxicity (AST > 1,000 U/L) without acute hepatic failure, and 6 patients with hepatotoxicity (AST > 1,000 U/L) with hepatic failure had acetaminophen halflives of 3.7 hours (range, 1.15~23.2 hours), 5.9 hours (range, 1.96~26.2 hours), 6.3 hours (range, 2.19~15.38 hours), and 32.8 hours (range, 5.48~103.9 hours), respectively (p<0.05). A receiver operating characteristic curve analysis showed that an acetaminophen halflife of 5.19 hours provided better discrimination (sensitivity=69.6%, specificity=84.0%, accuracy=80.6%).
The acetaminophen halflife correlates well with the degree of liver damage in patients treated with N-acetylcysteine. Longer halflives reflect a greater toxic effect on the liver.
Key words: Acetaminophen, Elimination halflife, N-acetylcysteine
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