Utilising paired measurements of phosphatidylethanol to monitor early success in alcohol abstinence

Phosphatidylethanol (PEth) is a specific and persisting marker of ethanol (alcohol) consumption. Early success of medically necessary abstinence can be assessed by monitoring PEth disappearance at a biologically plausible rate. This requires an understanding of PEth elimination, its variability and its determinants. To achieve this, we characterised PEth elimination in drinkers who voluntarily abstained. We aimed to derive a nomogram from the data to assist practitioners in recognising abstinence. Twenty-nine usual drinkers who were prepared to abstain from alcohol consumption for 4 weeks were recruited. Erythrocyte PEth was measured weekly. A population pharmacokinetic model for PEth was developed, describing the time-course of PEth elimination. Estimates were derived for population average, inter-individual variability in PEth half-life and any covariate influences. These estimates informed a nomogram of PEth elimination that incorporated a boundary separating continued abstinence from resumed drinking. The nomogram was tested to identify drinking events among participants. The model estimated a population average elimination rate constant (k) of 0.088 day , corresponding to a half-life of 7.9 days with a residual coefficient of variation of 8.5%. Elimination was first order and no covariate influences were identified. The nomogram was internally assessed as predictively accurate for 21 successfully abstinent participants and in detecting alcohol consumption in 2 further participants, using a 99.9% prediction interval. The value of PEth in distinguishing alcohol abstinence from consumption is enhanced by using a nomogram to confirm abstinence within weeks of its medically necessary imposition. Further work will establish the value of this approach in clinical practice.