J Korean Soc Emerg Med.  2003 Mar;14(1):56-60.

The Clinical Use of the Plasma Acetaminophen Halflife in NAC-treated Acetaminophen Overdose

• Lee SH
• Lee MJ
• Lee WJ
• Lee WJ
• Kim SK

Abstract

PURPOSE
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).
METHODS
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.
RESULTS
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%).
CONCLUSION
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.

Keyword

Acetaminophen; Elimination halflife; N-acetylcysteine

MeSH Terms

Acetaminophen*
Acetylcysteine
Discrimination (Psychology)
Half-Life*
Humans
Kinetics
Liver
Liver Failure
Liver Failure, Acute
Plasma*
ROC Curve
Acetaminophen
Acetylcysteine