Tobacco Documents Online

I I I I I I I I I I I I I I I I Daily intake of nicotine during cigarette smoking Daih• intake of nicotine in 22 subjects was estimated from metabolic clearance data obtained afrer intravenous infusion of nicotine and from blood and urinary nicotine concentration data obtained over 24 hr when the subjects were smoking cigarettes. Daily intake of nicotine averaged 37.6 mg (s17.7. SD) but varied widely among subjects (10.5 to 78.6 mg). Men metabolized nicotine faster than did women, but daily intake of nicerine did not differ. Intake correlated strongl}• with cigarettes smoked per dav (r = 0.59) but not with machine-determined yield. Nicotine intake per cigarene averaged 1.04 mg ( s0..36) but did not correlare with machine-determined yield. Correlations between several commonly used biochemical markers of tobacco smoke and nicotine intake were uamined; the afternoon (4:00 P.M.) blood level of nicotine was the best marker. Neal L. Benowitz, M.D., and Peyton Jacob 111, Ph.D. San Francisco, Calif. Clinical Pharmacology Division of the Medical Service, San Francisco General Hospital Medical Center. and the Langley Porter Psychiatric Institute and Deportment of Medicine, University of California The importance of nicotine in the mainte- nance of cigarette smoking behavior and its contribution to adverse effects of smoking are generally accepted, but no adequate methods for determining daily nicotine intake have been described. Nicotine intake from single ciga- rettes has been measured by spiking cigarettes with radiolabeled nicotine,' but is not applica- ble in the determination of nicotine consurnp- tion in natural smoking situations. Blood con- cxntrations of nicotine sampled throughout the day'- " are useful in estimating nicotine expo- sure, but translation of blood concentrations into intake is theoretically limited by the fact Suppoted c prs by gmac CA323l9 from drc Nstioatl Ganer tesuaae aod =raasc DA023T7 ud DA01696 tiom the Noaaeil lasti- aoe sa tku= Abuse. The sadirs wae ewrrod oui in the Geaeal Cliaial Researeh Cea, a at Sae Frinciuo Cxraal HoepisaJ Medinl Cema (RR-a0013) with support by the Diriiaa of Rexare4 Re- socrori. Nuionu imnnuea of Hald, R.osired tor pnblinuon Aug. 29.19E3; aeeepied Oct. 17,19i3. Repeiet taquesa to: F1eal L Beaowia. M.D.. Saa Psaaasco Geaeaa! Hoeyual A{edua! Ceaea. Buildia{ 30. Fihh floor. 1001 Poetro Ave.. San Fraacueo. CA 94110. that metabolic clearance varies considerably from person to person.' Thus a given blood concentration of nicotine may represent dose levels of nicotine that differ severalfold for dif- ferent people. We attempted to quantitate daily intake of nicotine by a method similar to that used in drug bioavailabiliry studies. Metabolic clearance of nicotine was determined after in- travenous injection. Metabolic clearance data were then used in conjunction with blood and urinary concentrations of nicotine measurod during a 24-hr period of smoking to determine the 24-hr intake of nicotine. We also examined relationships among daily intake of nicotine, daily exposure to nicotine (blood concentration of nicotine integrated over 24 hr), various pa- rameters of cigarette consumption, and different measures of nicotine intake that have been used by other investigators. Methods Our subjects were 13 men and nine women 22 to 55 yr old (33.4 = 12.5; X= SD). All 1 - - 499

I I I I I I I I I I I I 500 Benu-vt;, and JuCob MICOTINf IMfUSIOM 1.3 Ne14q/m/w so r'`• x CLr • ON.UC • 11N wd/w11w CL.• U.N/AUC • 72 wJ/wNw CLw. • CLr-Cl• • 1092 w.l/min W ? 0 U Z 0 0 0 m 0 50 t00 150 200 MINUTES 290 300 C6n Pharmn«l, rhrr .+/+n/ /O1fJ 30 20 10 Smo4.d 31 ciqer.tt.c AUC+341 wq•m{•l•hr'I Uwl, = s..ma CL. • V..Ir/AVC * 266 mI/mlw CLT • CLy.' CLc + 13{O mI/miw 0 a AUC ' CL, - 28.2 mq/Z4hr Nit/clq+0.91 mq 08ee 1200 1600 20ee 2 4ce 0400 0800 CLOCK TIME Fig. 1. Data and computations used to estimate daily intake of nicotine in one subject. A. Blood concentrations of nicotine durin¢ and after nicotine infusion. B. Blood concentrations of nicotine measured throughout the day during ad lib cigarette smoking. were habitual cigarette smokers who by history smoked at least one pack a day cf medium- to high•nicotine yield cigarettes (average U.S. Federal Trade Commission smoking machine yield 1.24 -_ 0.27 mg; range 0.87 to 1.80). Sub- jects were hospitalized in the General Clinical Research Center at San Francisco General Hospital Medical Center. They ate a normal diet except for caffeine-containing beverages and alcohol, which were prohibited. On the second hospita: day nicotine was infused intravenously to determine metabolic clearance. For the next 2 or 3 days subjects smoked their own brand of cigarettes as desired. All cig.arette butts were collected. Urine was collected each day for meamremmrtt *3f~aily excretton oT utCOtine and :otirmre (thl< major metabolite of nicotine). A circadian blood sampling study was performed on the last day of the study. Nicotine was in- fused after overnight abstinence from smoking as repotted:' L-Nicotine bitartrate. 1.5 µg base/k~:/min. was infused for 60 min. Blood samples were collected at frequent intervals and urine was collected for 5 hr after the end of the infusion. On smoking days subjects were given three or four packs of their usual brand of cigarettes each morning and told to smoke them in any manner they wished. On the day of blood sam- plino an indwelling butterfly catheter was in- serted into a forearm vein for collection of blood samples for measurement of concentra- tions of nicotine, cotinine, and carboxyhemo- globin. Blood samples were collected every 2 hr from 8:00 x.t1t. to midnight and then at 4:00 A.M. and 8:00 A.uW the next day. Time of blood sampling was independent of when the subjects smoked the last cigarette. To assess the ef- fects of blood collection on smoking behavior, counts of the number of cigarettes smoked and the urinary excretion of nicotine on the day be- fore were compared with those measured on the day of circadian blood sampling. Concentra- tions of nicotine and continine in blood and urine were measured by gas-liquid chromstog- raphy."' Carboxyhemogiobin level was mea- sured with an IL Model 280 Co-oximeter (In- xtrumentation Laboratory). Total (CL,). renal (CL„). and nonrenal (CL,,,) blood clearances of nicotine were computed by use of modcl-independent methods:` s The area under the blood concentration-time curve for I

t 1 1 ~ 1 ~ ~ I ~ ~ i 1 Vo/un,e JS Nuinbrr I 24 hr for nicotine (AUC) and carboxyhemo- globin was computed by the trapezoidal rule. CL, during the day of blood sampling was de- terrnined as the ratio of the 24-hr urinary excre- tion/AUC. Assuming that CL, was of the same order on the smoking and intravenous infusion days, Cl.f while smoking was estimated as the sum of CL,,,, measured during intravenous infu- sion plus CL„ measured during the day of cir- cadian blood sampling. Daily intake of nicotine (D) was then computed as D = (AUC) x(Cl,r). Average nicotine intake per cigarette was com- puted from D and the number of cigarettes smoked. The number of cigarettes smoked and urinary excretion of nicotine (U,,,,) on the day blood was drawn and on the preceding day were compared by paired t tests. Group differences were analyzed by t test or analysis of variance (ANOVA) as indicated in the text. Correlations between smoking parameters, markers of con• sumption, and nicotine intake and exposure were examined by linear regression. . Daily nicotine intake during cigarene smoking 501 Results Data illustrating computation of 24-hr intake of nicotine for one subject atr shown in Fig. 1. For the group, average CL.T on the smoking day was estimated as 20.5 = 5.0 ml/min/kg in men and 15.7 = 4.7 mi/min/kg in women (P < 0.05; Student's t test); both groups had more than 200% variation in clearance (Fig. 2). Sub- jects smoked an average of 36.5 = 12.5 ciga- rettes a day (20 to 62) on the day of circadian blood sampling and much the same number (35.9 = 11.3) on the day before, when thett was no blood sampling. The AUC for nicotine, a measurr of daily nicotine exposure, and D showed great individual variation (500% to 7004b) (Fig. 2), as expected in light of the known variation in cigarette smoking behavior. The D averaged 37.6 = 17.7 mg (10.5 to 78.6). Nicotine intake per ciga:ztte averaged 1.04 = 0.36 mg (0.37 to 1.56). Neither measurement diffeted between men and women. The U„, on the day before and the day of blood sampling did not differ significantly (2.8 = 1.9 and 3.6 = 1.8 mg/24 hr). Correlations between age, sex, filtered (N = 16) vs nonfiltered (N = 6) cigarette smoking, number of cigarettes smoked per day, and CLEARANCE (ml/min/kg) 32 . . 24 . • -1. . . T. AUC (ng-h/ml) ~'o°° . : ~ t~ 1 I ~.oe 1 ~ : .»~ M F ~"0 M F NICOTINE INTAKE (mg/24h) F60 : ~20 . M F Fig. 2. Total nicotine clearance, area under the blood nicotine concentration-time curve (a measure of daily nicotine exposure). and estimated daily intake of nicotine in 22 subjects, separated accordig to sex (M = male, F g female). Bars indicate X= SE. Analysis of sex differences was by t test. CIGARETTES PER DAY Fig. 3. Regression analysis of relationship between daily intake of nicotine and number of cigatsttes smoked in the study day. smoking machine yield' were examined. Only cigarettes per day correlated significantly with nicotine intake, but could account for only 35% of the total variance in nicotine intake (Fig. 3). Smoking machine yields of nicotine did not cor- relate significantly with either daily intake of nicotine (r = 0.16) or nicotine intake per ciga-

I I I I I I I I I I I ~ I I I I I 502 Benowitz and Jacob a 2.0 K 7 0 0 q•w•WM Uw. ,' a a I . 1.0 0 ts 2.0 0.5 0 MAC}iINE NICOTINE YIEID (mg) Fig. 4. Regression analysis of relationship between nicotine intake per cigarette and machine-determined nicotine yield." The solid line is the regression line. The dashed line is the line of identity, which indi- cates points at which measured nicotine intake per cigarette equals machine-detetmined nicotine yield. Table I. Correlation of various markers of robacco smoke intake with daily intake of nicotine and nicotine exposure Measure Time Intake AUC BNC 4 P.M. 0.81• 0.91 • BNC Noon 0.76' 0.90• COHB 4 P.M. 0.69• 0.81' COHB Noon 0.65• 0.82• Ur•, 24 hr 0.62• 0.46t COHB 8 A.M. 0.61 • 0.76' BNC 8 A.M. 0.56• 0.78• BM 4 P.M. 0.53t 0.45t Be« 8 A.M. 0.51t 0.39 24 hr 0.39 0.31 BNC • bloOd nieoe«i coxena>teia,: COHB - ccboiylxmo- globin krel: U,. - 24-hr une.ry uen:non of eaieune: bioc.i aotinn+e eoncencanon. •P<0.01:tP<0.03. rette (Fig. 4). Based on the observation that nicotine intake per cigarette was consistently less than machine yield, smoke:, of nonfiltered cigarettes. which have higher machine yields than filtered cigarettes, seemed to smoke their cigarettes less intensively than smokers of filtered cigarettes (Fig. 4). Mean ratios of Clin. Phannacol. Thrr. April 198s nicotine intake per cigarette/smoking machine yield for male nonfiltered, male filtered, and female filtered cigarette smokers (there were no female nonfiltered cigarette smokers) were: 0.54 ± 0.21, 1.01 = 0.36, and 1.02 = 0.32 (P < 0.05; ANOVA). Although smokers of filtered cigarettes smoked at an average rate close to that of the machine-predicted yield, the range of machine delivery was broad. 335e to 155%. Cottelations between D and AUC and a number of potential markers of tobacco smoke exposure were examined (Table 1). The best marker of nicotine intake and exposure was the blood concentration of nicotine measured at 4:00 P.H., followed by the concentration at noon. Carboxyhemoglobin concentrations at 4:00 P.M. and noon were the next best markers. Discussion We make several assumptions in our method of estimating D. First, we assume that clearance estimated during intravenous nicotine infusion is representative of clearance throughout the day while smoking cigarettes. There probably is variation in nicotine clearance from time to time during the day for all persons. The metabolism of drugs with rapid clearance such as nicotine is known to depend on liver blood flow and other circulatory factors. Thus it is likely that posture, meals, and perhaps the cardiovascular effects of nicotine itself, all of which could influence liver blood flow, could also influence nicotine clear- ance. We studied variation in nicotine clearance from day to day in four subjects (not in this study). When patients were studied on 2 sepa- rate days separated by 3 days, similar to the time frame of our study, we found an average within-subject difference in CL„, of nicotine of 3.4% (0.3% to 6.4%). Thus it is likely that there is much less variation within than among subjects. We anticipate, therefore, that the use of clearance measured during intravenous infusion of nicotine in the interpretation of blood concen- trations of nicotine during smoking will give a better estimate of nicotine consumption than would measurement of AUC during smoking alone. We assumed that the AUC based on mea- stuemenu every 2 hr accurately reflects the true 2046399011

I I I I I I ~ I I I I I I I I ~ I I va,u,,. is kanr xs ~ Daily nicotine intake during cigarette smoking 503 AUC cver 24 hr. Our method of sampling blood every 2 hr was selected to define the area with reasonable confidence but not to interfere ex- cessively with smoking behavior. By random sampling independent of when the subjects smoked cigarettes, we hoped to compensate for not being able to define fully peaks and troughs of blood concentrations of nicotine. It is likely, however, that we have erred more on the side of missing some of the area under the peaks and, thus, have probably underestimated the true AUC. It can be argued that the distribution nicotine tlk is much shorter (8 min) than the elimination 0/i (120 min), so that the area missed by not sampling the peak is relatively small compared to the total AUC. As expected, we iound marked individual differences in AUC and D that were sig- nificantly correlated (r = 0.81; P < 0.001). For most subjects there was a reasonably good cor- rtlation between nicotine intake and exposurr, but extremes of CLr differed by 300°k. Thus a person with low CLT would need to smoke only one third as much as a person with high CL, to achieve the same level of nicotine exposure. Although our sample size was relatively small, our data suggested that clearance (normalized for body weight) is lower in female than in malt smokers. We found no sex difference in D, but because of lower CI,t ther= was a tendency for levels of nicotine exposure to be higher in women. Analysis of smoking parameters that might predict D showed correlations of number of cigarettes smoked, but not smoking machine- determined yields, with nicotine intake. Other studies have shown that cigarettes per day but not machine-determined yields correlate with levels of carboxyhemoglobin or expired carbon monoxide,"• '2 plasma or salivary concentra- tions of thiocyanate,"- '= blood levels of nic- otine," and blood or urinary levels of coti- nine!• '= That the number of cigarettes smoked per day accounted for only 35% of the variance in nicotine intake is consistent with the thesis that how cigarettes are smoked is mon: impor- tant than how many cigarettes are smoked.' The lack of correlation between U.S. Federal Trade Commission smoking machine-deter- mined yield and intake of nicotine per cigarette ft can easily be understood because people and machines smoke cigarettes differently. We found that the average intake of nicotine per cigarette was about I mg, much the same as the average smoking machine yield for the filtered cigarettes smoked. In our populadon smokers of nonfiltered cigarettes seemed to smoke ciga- rettes such that nicotine intake was consistently less than machine-determined nicotine yield, which in turn was higher for nonfiltered than for filtered cigarettes. Total D did not differ for smokers of filtered and ot nonftltered cigarettes. Validation of biochemical markers of nico- tine intake and exposure is important. Simple, inexpensive measures are desirable for studies of smoking in the natural environment, particu- larly for large-scale epidemiologic studies. Our data indicate that afternoon nicotine or car- boxyhemoglobin levels are reliable markers of nicotine intake and exposure. To our surprise morning levels correlated significantly with D, presumably because of the overnight persis- tence of nicotine and carbon monoxide in the blood from the day before.' Although cotinine is a highly specific marker for nicotine expo- sure, blood level of cotinine (B,,,t) was not as good a marker of nicotine intake as blood levels of nicotine or carboxyhemoglobin. This is pre- sumably a result of individual variation in the fractional conversion of nicotine to cotinine and in the rate of elimination of cotinine itself. For longitudinal within-subject studies, however, we still expect cotinine levels to be good mark- ers of changes in nicotine intake. As expected by the known variation in CL, from effects of urine flow, pH, and individual differences,=•'-i0 U„i, did not correlate with nicotine intake or exposure. In contrast, urinary excretion of cotinine, which is less influenced by urinary flow and pH,=•' was as good a marker as B., We acknowledge the technical assistance of Chin Savanapridi and Beverly Busa. and the statistical as- sistance of Richard Cohen. References 1. Armitage AK. Dollery CT. George CF. House- man T'H, Lewis PJ, Turner DM: Absorption and metabolism of nicotine from cigarettes. Br Med J a:313-316,1975. 2. Beckett AH, GotTod JW, Jenner P: A possible

I I I I I I I I I I I I I I 504 Benowin and Jacob relation between pKa and lipid solubiliry and the amounts excreted in urine of some tobacco ai- kaloids given to man. J Pharrn Pharmacol 24:115-120. 1972. 3. Benet LZ. Galeazzi RL: Noncompattmental de- termination of the steady state volume of distri- bution. J Phatm Sci 68:1071-1074, 1979. 4. Benowitz NL, Hall SM, Herning RI, Jacob P, Jones RT, Osman A-L: Smokers of low-yield cigarettes do not consume less nicotine. N Engl J Med 309:139-142, 1983. 5. Benowitz NL, Jacob P, Jones RT, Rosenberg I: Intecindividual variability in the metabolism and cardiovascular effects of nicotine in man. J Pharmacol Exp Ther 221:368-372. 1982. 6. Benowitz NL. Kuyt F, Jacob P: Circadian blood nicotine concentrations during cigarette smok- ing. CLIN PHARMACOL THER 32:758-764, 1982. 7. Benowitz NL. Kuyt F, Jacob P. Jones RT, Ostttan A-L: Cotinine disposition and effects in humans. CLiN PHARMACOL THER 34:604-611, 1983. 8. Federal Trade Commission: Report of "tar," nicotine and carbon monoxide of the smoke of 200 varieties of cigarettes. Washington, D.C.. 1981, U.S. Federal Trade Commission. 9. Herning RI. Jones RT, Benowitz NL. Mines ciin. Pharnracd. Thr Aprnr r9& AH: How a cigarette is smoked determines blood nicotine levels. CLIN PHARMACOL THER 33:84-90, 1983. 10. Jacob P. Wilson M. Benowitz NL: Improved gas chromatographic method for the determination of nicotine and cotinine in biologic 8uids. J Chromatogr 222:61-70, 1981. 11. Jaffe JH, Kanzler M, Friedman L, Stunkard AJ. Vereby K: Carbon monoxide and thiocyanate levels in low tar/nicotine smokers. Addict Behav 6:337-343, 1981. 12. Rickert WS. Robinson JC: Esdtnating the haz- ards of less hazardous cigarettes. II. Study of cigarette yields of nicotine, carbon monozide, and hydrogen cyanide in relation to levels of cotinine. carboxyhemoglobin. and thiocyanate in smokers. J Toxicol Environ Health 7:391- 403. 1981. 13. Rosenberg J, Benowitz NL. Jacob P, Wilson KM: Disposition kinetics and effects of intrave- nous nicotine. CLIN PHARMACOL THER 28:517- 522. 1980. 14. Russell MAH. Jarvis M. Iyer E. Feyerabend C: Relation of nicotine yield of cigarettes to blood nicotine concentrations of smokers. Br Med J 2130:972-976, 1980.