The effect of smoking on theophylline kinetics in healthy and asthmatic elderly males.

The effect of smoking on theophylline kinetics was investigated in four groups of males over the age of 65 yr. The first group consisted of 14 healthy non-smoking males, the second group consisted of 8 healthy smoking males. The first and the second groups were administered a single oral dose of 300 mg tablet of sustained-release anhydrous theophylline product and serial blood samples were collected over 24 hr. The third group consisted of 22 clinically stable asthmatic non-smoking males, the fourth group consisted of 9 clinically stable asthmatic smoking males. The third and the fourth groups, were administered multiple oral doses equivalent to 300 mg of anhydrous theophylline from sustained-release Oxtriphylline every 12 hr for 72 hr; and blood samples were collected every two hours between 72-82 hrs. Serum theophylline concentrations were determined by HPLC. There were no significant differences between the smokers and non-smokers in observed maximum concentration (Cmax), its time (tmax), the area under the time-concentration curve (AUCo-t), and total body clearance rate (Cl). Aging appears to offset the known smoking inducing effect on the hepatic microsomal enzymes.