Effects of passive smoking on theophylline clearance

Theophylline disposition was examined in seven passive smokers, defined as nonsmokers with long-term exposure to cigarette smoke, and seven age-matched nonsmokers with minimal smoke exposure. Subjects were given an intravenous infusion of aminophylline (6 mg/kg) and blood samples were drawn before and during the 48-hour postinfusion period. Clearance for passive smokers was 6.01 × 10^-2 L/hr · kg and for nonsmokers, clearance was 4.09 × 10^-2 L/hr · kg (p < 0.025). Terminal elimination half-life for passive smokers was 6.93 hours versus 8.69 hours for nonsmokers (p < 0.05). The mean residence time for passive smokers was 9.89 hours. For nonsmokers, the mean residence time was 13.11 hours (p < 0.05). These measurements were statistically different, whereas there was no difference in volume of distribution between the groups, suggesting that passive smokers metabolize theophylline more rapidly than nonsmokers. Plasma and urine cotinine and nicotine concentrations were measured in all subjects. There was a significant difference between the subject groups in plasma (p < 0.004) and urine (p < 0.002) cotinine concentrations. Theophylline clearance correlated with both plasma (r = 0.73, p < 0.01) and urine (r = 0.79, p < 0.01) cotinine concentrations. Additional studies should be conducted to further define the pharmacokinetic characteristics of passive smokers and to assess the effects of passive smoking on drugs metabolized by the mixed function oxidase system.