In the Pharmacokinetics in Twins (“PKTWIN”) [58] study, participants were recruited from the Northern California Twin Registry in a multiple stage protocol to coordinate ascertainment of twins to investigate heritability and genetic components of nicotine metabolism. Participants consented to a 30-min venous administration of nicotine and cotinine, followed by an 8-hour hospital stay for blood and urine biosample collection. In the Pharmacogenetic Study of Nicotine Metabolism (“588”) [57], recruiting by smoking status and gender of European, African, and Asian Americans was performed through multi-media advertisements for a nicotine and cotinine metabolism study. Participants consented to morning oral administration of nicotine, and either labeled (smokers) or unlabeled (nonsmokers) cotinine. The following biospecimens were collected: saliva up to 60 h after dosing; blood up to 480 min; urine up to 8 h. In the Smoking in Families (SMOFAM) study [59], individuals from 61 pedigrees with at least three ever-smokers individuals per pedigree originally recruited to assess the relations among genetic factors, environmental factors, and tobacco use, consented to oral administration of a fixed dose of nicotine and cotinine at home monitored by
