Cigarettes are harmful for people’s health but they are more injurious when are smoked in big amounts. Half a pack of cigarettes per day can increase clopidogrel (an oral antiplatelet agent to inhibit blood clots in coronary artery disease, peripheral vascular disease, and cerebrovascular disease) efficacy, according to a recent study.

Clopidogrel is a prodrug that is metabolized in the liver in 2 steps to its active metabolite. The active metabolite binds irreversibly to platelet receptors to inhibit platelet aggregation. However, patients with highly reactive platelet receptors have been demonstrated to have higher rates of ischemic events after PCI.

Smoking at least half a pack of cigarettes a day can increase the effectiveness of clopidogrel especially in patients who have had a heart attack, showed in a study researchers.

Nihar R. Desai, M.D., from Brigham and Women's Hospital in Boston, and his colleagues examined whether cigarette smoking affected the efficacy of clopidogrel in 3,429 patients with ST-segment elevation myocardial infarction who were randomized to placebo or clopidogrel as part of a clinical trial.

They note that smoking induces an enzyme that activates clopidogrel, and an earlier study had shown that smoking at least 10 cigarettes per day resulted in greater inhibition of platelet accumulation.

The researchers found that although clopidogrel was effective in reducing the rate of closed infarct-related artery or death or myocardial infarction before angiography, the drug was even more effective in the 1,491 patients who smoked at least 10 cigarettes per day (adjusted odds ratio, 0.49 versus 0.72). Clopidogrel was also more effective in reducing the risk of cardiovascular death, myocardial infarction, or urgent revascularization in 30 days in patients who smoked at least 10 cigarettes per day.

This study demonstrated that common clinical factors that influence the metabolism of clopidogrel might impact its clinical effectiveness. Cigarette smoking seems to positively modify the beneficial effect of clopidogrel on angiographic and clinical outcomes, researchers concluded.