Nicotine metabolism inversely linked to addiction severity in teens

By Mark Cowen, Senior medwireNews Reporter

Reduced nicotine metabolism is associated with a greater number of cigarettes smoked per day and increased levels of dependence in adolescent smokers, researchers report.

The findings, published in Addiction, contrast with those from studies of adult smokers, in which faster rates of nicotine clearance are generally associated with a greater number of cigarettes smoked per day.

"It is possible that there is something unique about this period of brain development that influences an adolescent's response to nicotine exposure," say Mark Rubinstein (University of California, San Francisco, USA) and colleagues.

The team studied 164 adolescent smokers, aged 13-17 years, who were assessed for nicotine dependence using the modified Fagerström Tolerance Questionnaire (mFTQ), with higher scores on a scale of 0-7 indicating greater nicotine dependence.

Saliva samples collected 8 hours after oral administration of a deuterium-labeled cotinine solution were used to calculate each patient's nicotine metabolite ratio (NMR).

The participants reported smoking an average of 2.86 cigarettes per day, with 18% smoking five to 10 and 4% smoking 10-20 cigarettes per day. The mean duration of smoking was 1.37 years, the mean mFTQ score was 2.61, and the mean NMR value was 0.17.

After accounting for age, gender, duration of smoking, and ethnicity, the team found that NMR was significantly and inversely associated with the number of cigarettes per day. Indeed, each 1-point increase in NMR was associated with a decrease of 3.61 cigarettes per day.

The nicotine metabolite ratio was also significantly and inversely associated with mFTQ scores, such that the faster the metabolism rate, the lower the mFTQ score.

Rubinstein et al conclude: "Our results suggest that, during adolescence, slower clearance of nicotine may promote rather than impede the development of addiction, perhaps mediated by higher levels of nicotine exposure per cigarette."

They add: "The current findings highlight the importance of studying smokers at various stages of smoking progression."

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