Drug Interactions With Smoking

Lisa A. Kroon, Pharm.D


Am J Health Syst Pharm. 2007;64(18):1917-1921. 

In This Article

Potential for Drug Interactions After Smoking Cessation

After a person quits smoking, an important consideration is how quickly the induction of CYP1A2 dissipates. This is particularly important when a patient is hospitalized and abruptly quits smoking. Faber and Fuhr[6] studied CYP1A2 activity, using caffeine clearance, in 12 subjects who smoked at least 20 cigarettes daily (range, 22.3-27.7 cigarettes). At days 1, 2, 3, and 4 and at steady state (approximately one week), the relative reduction in CYP1A2 activity was 12.3%, 20.1%, 25.0%, 28.2%, and 36.1%, respectively. The half-life of CYP1A2 activity after smoking cessation was 38.6 hours. The authors recommended a 10% daily-dose reduction for drugs that are CYP1A2 substrates until the fourth day after smoking cessation. This is a conservative approach and can be considered for drugs with a narrow therapeutic range, such as theophylline. It is important to note that the subjects in the Faber and Fuhr[6] study were heavy smokers. It is not known how the amount of cigarettes smoked daily or interindividual variation affects CYP1A2 induction. Given the short length of stay for many hospitalized patients, practitioners should consider the potential for some degree of persistence of CYP1A2 induction during hospitalization.

As a general approach, practitioners should consider a dosage reduction of drugs that are CYP1A2 substrates for a person who quits smoking. Conversely, if a person begins smoking and is taking a drug that is a CYP1A2 substrate, the dosage may need to be increased.


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