Interlaboratory comparability of serum cotinine measurements at smoker and nonsmoker concentration levels: a round-robin study.

INTRODUCTION: Cotinine, the primary proximate metabolite of nicotine, is commonly measured as an index of exposure to tobacco in both active users of tobacco and nonsmokers with possible exposure to secondhand smoke (SHS). A number of laboratories have implemented analyses for measuring serum cotinine in recent years, but there have been few interlaboratory comparisons of the results. Among nonsmokers exposed to SHS, the concentration of cotinine in blood can be quite low, and extensive variability in these measurements has been reported in the past. METHODS: In this study, a group of seven laboratories, all experienced in serum cotinine analysis, measured eight coded serum pools with concentrations ranging from background levels of about 0.05 ng/ml to relatively high concentrations in the active smokers range. All laboratories used either gas-liquid chromatography with nitrogen-phosphorus detection or liquid chromatography with mass spectrometric detection. RESULTS: All seven laboratories reliably measured the cotinine concentrations in samples that were within the range of their methods. In each case, the results for the pools were correctly ranked in order, and no significant interlaboratory bias was observed at the 5% level of significance for results from any of the pools. DISCUSSION: We conclude that present methods of chromatographic analysis of serum cotinine, as used by these experienced laboratories, are capable of providing accurate and precise results in both the smoker and the nonsmoker concentration range.

Relative bioavailability and pharmacokinetics of two oral formulations of docosahexaenoic acid/eicosapentaenoic acid after multiple-dose administration in healthy volunteers.

OBJECTIVES: To assess the comparative pharmacokinetic profile and bioavailability of docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) after multiple-dose administration of a new oral formulation (test formulation) and a commercially available reference formulation in healthy subjects. METHODS: Forty-eight healthy subjects received a 28-day oral treatment with DHA/EPA in the form of either the test or the reference product according to an open-label, randomized, parallel-group design. Both formulations were given t.i.d. at 8-h intervals at a dose of 3.0 g/day. Steady-state DHA and EPA concentrations in plasma and lysed whole blood were measured by gas-liquid chromatography at baseline and after 7, 14, 21 and 28 days of treatment. Kinetic parameters were compared both after subtraction of baseline concentrations and by using baseline concentrations as a covariate. RESULTS: For both DHA and EPA, plasma and RBC concentrations measured from day 7 to day 28 were significantly higher than at baseline and did not differ significantly between the two products. On day 28 the plasma DHA concentration on average doubled the baseline level after administration of test and reference product, while there was a 10-fold increase in EPA plasma concentration. When the assessment was performed using baseline values as covariate, test-to-reference ratios for area under the curve (AUCss(0-8)) and for peak concentration (Css(max)) after the last administration on day 28 met bioequivalence criteria (i.e., 90% confidence intervals within 0.80-1.25 for AUCss(0-8) ratios, and within 0.75-1.33 for Css(max) ratios). When the assessment was conducted after subtraction of baseline values, the 90% confidence intervals for Css(max) ratios were within the bioequivalence range, whereas the intervals for AUCss(0-8) ratio were borderline for bioequivalence. CONCLUSION: The two formulations tested were similarly effective in increasing DHA and EPA concentrations in plasma and lysed whole blood, and showed comparable bioavailability for both active components.

Collaborative Method Performance Study of the Measurement of Nicotine, Its Metabolites, and Total Nicotine Equivalents in Human Urine.

Background: Biomarkers of tobacco exposure have a central role in studies of tobacco use and nicotine intake. The most significant exposure markers are nicotine itself and its metabolites in urine. Therefore, it is important to evaluate the performance of laboratories conducting these biomarker measurements.Methods: This report presents the results from a method performance study involving 11 laboratories from 6 countries that are currently active in this area. Each laboratory assayed blind replicates of seven human urine pools at various concentrations on three separate days. The samples included five pools blended from smoker and nonsmoker urine sources, and two additional blank urine samples fortified with pure nicotine, cotinine, and hydroxycotinine standards. All laboratories used their own methods, and all were based on some form of liquid chromatography/tandem mass spectrometry.Results: Overall, good agreement was found among the laboratories in this study. Intralaboratory precision was good, and in the fortified pools, the mean bias observed was < + 3.5% for nicotine, approximately 1.2% for hydroxycotinine, and less than 1% for cotinine (1 outlier excluded in each case). Both indirect and direct methods for analyzing the glucuronides gave comparable results.Conclusions: This evaluation indicates that the experienced laboratories participating in this study can produce reliable and comparable human urinary nicotine metabolic profiles in samples from people with significant recent exposure to nicotine.Impact: This work supports the reliability and agreement of an international group of established laboratories measuring nicotine and its metabolites in urine in support of nicotine exposure studies. Cancer Epidemiol Biomarkers Prev; 27(9); 1083-90. ©2018 AACR.