Smoking reduces serum levels of lamotrigine.

The influence of smoking on lamotrigine (LTG) serum levels in 44 patients with epilepsy treated with LTG in monotherapy was examined. Fifteen patients were smokers (range: three cigarettes per month -- three packages per day) and 29 were non-smokers. Analyzing 204 samples, smokers had a significantly lower serum level-to-dose ratio than non-smokers (0.0657mmolmg/l (smokers) vs. 0.0785mmolmg/l (non-smokers)) (p=0.0014). Analyzing only male patients, the same relationship with an almost equally high level of significance could be demonstrated (p=0.008). Our data indicate that the demonstrated effect of smoking on LTG metabolism is likely to be mediated via UDPGT2B7, as LTG is not a substrate of cytochrome P450 isoenzymes and UDPGT1A4 activity may not be affected by nicotine, but the exact mechanism underlying the demonstrated effect remains uncertain. These findings are likely to be independent from hormonal changes, as they could also be reproduced in the group of male patients. Therefore, the effect of smoking on blood levels of LTG has to be taken into account in the evaluation of treatment with this drug.