Estimated risk of hepatotoxicity after an acute acetaminophen overdose in alcoholics.

A published logistic regression model based on the Canadian Acetaminophen Overdose Study registry was used to calculate the risk of hepatotoxicity after an acute acetaminophen overdose and to estimate a treatment threshold line for alcoholic patients who did not co-ingest alcohol (i.e., abstinent alcoholics) on the Rumack-Matthew nomogram. The risk of hepatotoxicity in nonalcoholic and abstinent alcoholic patients was calculated at the acetaminophen concentration of 150 microg/ml at 4h (37.5 microg/ml at 12h) treatment threshold line. This corresponds to the "possible risk" line on the Rumack-Matthew nomogram and represents a 1.6% risk of hepatotoxicity for nonalcoholic patients at or below this line. At or below this same 150 microg/ml at 4-h line, abstinent alcoholic patients have a hepatotoxicity risk of 10.7%. The risk of hepatotoxicity in abstinent alcoholics' equivalent to that of nonalcoholics (i.e., 1.6%) occurs at a lower acetaminophen concentrations treatment threshold line, that is, 104 microg/ml at 4h (26 microg/ml at 12h). Because of difficulties plotting this new line on the familiar Rumack-Matthew semilogarithmic scale, a line connecting 100 microg/ml at 4h (25 microg/ml at 12h) is proposed. This line equates to a 1.1% risk of hepatotoxicity in abstinent alcoholic patients. The analysis supports the observation that based on the published model abstinent alcoholics might have a greater risk of hepatotoxicity after an acute acetaminophen overdose. This proposed new risk line can be used in hypothesis generation for future clinical studies in this alcohol related problem.