Estimating human pharmacokinetic parameters for electronic nicotine delivery system products from chemical analyses...

The ability of Electronic Nicotine Delivery Systems (ENDS) to deliver nicotine is central to their function to substitute for cigarettes, allowing people who smoke to switch away from smoking, thus reducing their exposure to harmful chemicals in cigarette smoke. The nicotine concentration in ENDS e-liquid has proved to be a poor predictor of nicotine uptake in users. Using meta-analytic methods to analyze 12 pharmacokinetic studies of nicotine-salt closed-system ENDS, this paper examines whether the mass of nicotine/puff of aerosol can predict C_max in pharmacokinetic studies. C_max values were available for 38 products, in 58 use conditions (including both controlled [3 s] and ad libitum puffing), comprising 1769 participant observations. Nicotine/puff data reflected chemical analyses of aerosol obtained under nonintense (3 s) or intense (6 s) machine puffing. Meta-regression analyses (weighted by reliability of C_max estimate) assessed the relationship of nicotine/puff to C_max. In some models, empirical data were used to impute the variation in C_max or the nicotine/puff value under intense puffing. In simple linear models, C_max was significantly associated with nicotine/puff under all combinations of intense/nonintense and controlled/ad-libitum conditions, with R² values of 0.71-0.77. More complex models based on quadratic effects or log[nicotine/puff] did not generally improve upon more parsimonious linear models. Application of the model illustrates the divergence between nicotine concentration in e-liquids and expected C_max when other ENDS parameters vary. The meta-analytic model may have utility in settings where clinical pharmacokinetic data are not available, including product development.