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E-cigarettes: an evidence update <br /> <br />72 <br />Speed of nicotine delivery seems important for smokers’ satisfaction. Cigarettes deliver <br />nicotine very fast via the lungs. It is likely that to out-compete cigarettes, EC will need to <br />provide nicotine via the lungs as well. Although some EC products may already provide <br />a degree of lung absorption, most nicotine is probably delivered via a much slower route <br />through buccal mucosa and upper airways, in a way that is closer to the delivery from <br />nicotine replacement medications than to the delivery from cigarettes. <br /> <br />This tallies with two other observations. Vapers feel they are less dependent on EC than <br />they were on cigarettes [126]; and non-smokers experimenting with EC do not find them <br />attractive and almost none progress to daily vaping [127]. This contrasts with the fact <br />that about half of adolescents who experiment with cigarettes progress to daily smoking <br />[128]. <br /> <br />In addition to mechanical characteristics of EC and user puffing behaviour discussed in <br />previous sections, the composition of the chemicals used to produce the vapour, <br />typically vegetable glycerol and/or propylene glycol (PG), may also influence nicotine <br />delivery. E-liquid with a mix of vegetable glycerol/PG was associated with better nicotine <br />delivery than a vegetable glycerol-only e-liquid with the same concentration of nicotine <br />[129]. The presumed effect is that PG vaporises at a faster rate than vegetable glycerol <br />when heated in the EC and so is able to carry more nicotine to the user. <br /> <br />If EC continue to improve in the speed of nicotine delivery, they are likely to appeal to <br />more smokers, making the switch from smoking to vaping easier. It may be important in <br />this context to note that if the smoking-associated risk is removed, nicotine use by itself, <br />outside pregnancy, carries little health risk and in fact conveys some benefits. <br /> <br />Table 8: Studies examining nicotine intake in vapers <br /> <br />Study Participants EC Device Methods Results <br />Vansickel <br />et al 2012 <br />[119] <br />20 <br />smokers <br />naïve to <br />EC <br />Vapor King <br />(cigalike), <br />18mg/ml nicotine <br />Overnight abstinence, <br />baseline blood sample, <br />after 5 mins 10 puffs, <br />30 sec inter-puff <br />interval, 5 mins after <br />last puff blood sample. <br />Repeated 5x, 30 mins <br />in between <br />At end of last <br />puffing bout <br />plasma nicotine <br />increased from <br />2.2 ng/ml at <br />baseline to 7.4 <br />ng/ml. <br /> <br />Vansickel <br />& <br />Eissenberg <br />2012 [121] <br />8 vapers <br />using EC <br />for <br />average <br />of 12 <br />months <br />Own EC <br />1 used 9 mg/ml <br />6 used 18 mg/ml <br />1 used 24 mg/ml <br /> <br />Overnight abstinence, <br />Baseline blood, after 5 <br />mins 10 EC puffs at 30 <br />sec intervals, 5 and 15 <br />mins after first puff <br />blood sample, 60 min <br />ad-lib vaping <br />Increase in <br />plasma nicotine <br />from 2.0 ng/ml to <br />10.3 ng/ml in 5 <br />mins. Cmax = <br />16.3 ng/ml at end <br />of ad lib period <br />Yan & <br />D’Ruiz <br />2014 [129] <br /> <br />23 <br />smokers <br />4 types of Blu <br />(cigalike) EC <br />(1.6% to 2.4%) <br />Marlboro cigarette <br />Randomised 6 sessions <br />7-days get used to EC, <br />36 h abstinence. EC = <br />50x5 sec puffs, 30 sec <br />During controlled <br />puffing Cmax <br />(ng/ml): EC 10.3 <br />to 18.9; cig 15.8