Effect of smoking on theophylline disposition.
The pharmacokinetics of theophylline were examined in a group of nonsmokers and in heavy smokers (1 to 2 packs/day) before and 3 to 4 mo after cessation of cigarette smoking. The half-life of theophylline in smokers averaged 4.3 (SD = 1.4) hr, significantly shorter than the mean value in nonsmokers (7.0, SD =1.7 hr). The apparent volume of distribution of theophylline was somewhat larger in smokers (0.50 +/-0.12 L/kg) than in nonsmokers (0.38 +/-0.04 L/kg). The body clearance of theophylline was appreciably larger and relatively more variable in smokers (100 +/-44 ml/min/1.73 m2) than in nonsmokers (45 +/-13 ml/min/1.73 m2). Serum concentrations of thiocyanate, a biotransformation product of cyanide which is inhaled with smoke, were used to monitor the smoking status of the subjects. The body clearances of theophylline showed a good correlation (r = 0.785, p less than 0.001) with the serum thiocyanate concentrations. Of the 8 smokers, only 4 managed to refrain from smoking for at least 3 mo, and these subjects showed no significant change in theophylline elimination. The increase in theophylline clearance caused by smoking is probably the result of induction of drug-metabolizing enzymes that do not readily normalize after cessation of smoking.
D000328:Adult; D005260:Female; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D008297:Male; D012463:Saliva / Q000378:metabolism; D012907:Smoking; D013806:Theophylline / Q000097:blood / Q000378:metabolism*; D013861:Thiocyanates / Q000097:blood
D013861:Thiocyanates; D013806:Theophylline