Prediction of acetaminophen level from clinical history of overdose using a pharmacokinetic model

A retrospective study was undertaken to determine the accuracy of predicting acetaminophen levels using the pharmacokinetic equation for first-order absorption and elimination of a single oral ingestion, (Formula: see text) Forty-four acute adult acetaminophen overdoses were studied during a 22-month period. Eighty levels drawn from 0 to 16 hours after ingestion were evaluated. To standardize the data, only first levels drawn in patients without prior spontaneous or ipecac-induced vomiting were analyzed (n = 26). Of these 26 levels, eight (31%) were drawn from 0 to two hours after ingestion, eight (31%) from two to four hours, and ten (38%) from four to 16 hours, with correlations of 0.59, 0.85, and 0.98, respectively. To determine the accuracy of predicting four-hour levels, five patients with first levels drawn at four hours, prior to vomiting, were evaluated. Substituting appropriate constants, the condensed equation, Cp4h = (0.59) (mg/kg dose), was used to predict the four-hour level (r = 0.99). Preliminary data suggest the ability to accurately predict four-hour acetaminophen levels from ingestion history alone using pharmacokinetic equations.